Materials glossary. Plain-English definitions of the terms used across the sectors we cover.

A reinforcement woven with yarns running in the thickness direction as well as in the plane, producing a near net shape preform with through thickness reinforcement. It improves damage tolerance and resistance to delamination and is used in demanding aerospace components such as fan blades and structural joints, usually with liquid moulding processes.

Surface preparation in which abrasive particles such as grit, shot or garnet are propelled at high velocity against a surface using compressed air or centrifugal wheels, removing rust, mill scale and old coatings while creating a surface profile. The achieved cleanliness is assessed against standardised preparation grades.

Laboratory exposure of materials to intensified ultraviolet light, moisture and heat cycles, using fluorescent UV or xenon arc apparatus, to simulate outdoor weathering in a compressed timescale. Methods are standardised in the ISO 4892 and ASTM G154 and G155 series, and results are used to compare colour retention, gloss loss, chalking and embrittlement of coatings, membranes and composites.

An additive that speeds the cure of a resin or adhesive, allowing curing at lower temperatures or in shorter times. Cobalt salts are the usual accelerators for polyester resins, working in combination with the peroxide catalyst; pre-accelerated resins have the accelerator already blended in by the manufacturer.

The building of parts layer by layer directly from digital models, using processes such as material extrusion, powder bed fusion and photopolymerisation. In advanced materials work it produces polymer, metal and fibre-reinforced components as well as jigs, fixtures and mould tooling.

A material applied as a very thin layer, or added to a formulation, to improve the bond between a coating or adhesive and a difficult substrate. Examples include silane coupling agents for glass and metals and chlorinated polyolefins for low surface energy plastics such as polypropylene.

Honeycomb core made from thin aluminium foil expanded or corrugated into cells, giving high stiffness and strength at very low weight together with predictable crush behaviour. It is used in aerospace structures, transport flooring and architectural panels, and its controlled collapse also makes it useful as an energy absorber.

A greasy or waxy film that can form on the surface of curing epoxy when amine hardeners react with carbon dioxide and moisture in the air, particularly in cool, damp conditions. It must be removed, usually by washing with water, before overcoating or bonding, as it destroys intercoat adhesion.

A polymer whose molecular chains have no long-range order. Amorphous polymers soften gradually above their glass transition temperature rather than melting sharply, and many, such as polycarbonate and acrylic, are naturally transparent.

The variation of a material's properties with direction. Fibre-reinforced composites are strongly anisotropic, with much higher stiffness and strength along the fibre direction than across it, so ply orientations must be matched to the expected load paths.

An electrolytic process that thickens and controls the natural oxide film on aluminium and certain other metals, improving corrosion and wear resistance and allowing the surface to be coloured by dyeing before sealing. It is widely specified for architectural aluminium and for aerospace components.

A coating applied to ship hulls and other immersed structures to prevent or reduce the settlement and growth of marine organisms. Most systems either release biocides in a controlled way or present a low energy foul release surface from which organisms are easily dislodged.

A zirconia containing glass fibre formulated to resist attack by the highly alkaline environment of cementitious matrices. It is the standard reinforcement for glass fibre reinforced concrete (GRC) and is also used in renders, screeds and repair mortars.

A synthetic fibre spun from aromatic polyamide, best known in its para-aramid form. It combines high tensile strength and toughness with excellent impact and abrasion resistance, though it is sensitive to ultraviolet light, absorbs moisture and is notoriously difficult to cut and machine. It is widely used in ballistic protection, ropes and hybrid composite laminates.

Honeycomb core manufactured from aramid paper coated with phenolic resin, producing a light, tough, non-metallic core with good fire resistance and electrical insulation. It is widely used in aircraft interiors and secondary structures, motorsport panels and marine interiors.

The mass of a fabric, mat or fibre layer per unit area, normally quoted in grams per square metre. It is the primary way reinforcements are specified and, together with fibre volume fraction, determines the cured thickness of each ply.

Standards developed by ASTM International, a US-based standards organisation whose test methods are used worldwide, particularly in aerospace and composites, for example ASTM D3039 for tensile testing of polymer matrix composites. Datasheets often quote both ASTM and ISO methods; results are broadly comparable but not always directly interchangeable.

The curing of composite laminates in a heated pressure vessel, which applies elevated temperature and gas pressure in addition to vacuum-bag consolidation. The combination suppresses voids and delivers the high, repeatable laminate quality required for primary aerospace structures.

A robotic process that lays narrow tows of prepreg or dry fibre onto a tool surface under controlled heat, pressure and tension, steering each tow individually. It enables complex curvature and tailored fibre paths on large structures with high deposition accuracy and low material waste.

A machine process that deposits wide unidirectional prepreg tape onto flat or gently contoured tooling, cutting and restarting the tape automatically at ply boundaries. It achieves very high lay-down rates on large, low-curvature parts such as wing skins and panels.

The flexible, airtight polymer film that forms the outer membrane of a vacuum bag, sealed to the tool with sealant tape. Films are selected for cure temperature capability, elongation and puncture resistance, and pleats are added so the film can conform to the part without bridging.

A laminate that contains, for every angled ply, a matching ply at the equal and opposite angle, eliminating coupling between in-plane extension and shear. Balanced, symmetric laminates are the default choice where predictable, distortion-free behaviour is required.

Loose material, typically rounded gravel or paving slabs, laid over a roof membrane or over inverted roof insulation to hold the system down against wind uplift and to protect it from ultraviolet light and mechanical damage. Ballasted systems avoid fasteners and adhesives but add significant dead load and make leak tracing more difficult.

Core material cut from balsa, a fast-growing tropical hardwood whose naturally cellular structure gives high compressive and shear strength for its weight. It is normally supplied as end-grain sheets or scrim-backed blocks, and as a renewable material it is often selected where sustainability is a factor.

A surface hardness measurement made with a handheld impressor that presses a sharp steel indenter into the material, standardised in ASTM D2583 and EN 59. In the composites industry it is widely used as a quick workshop or site check of laminate and gelcoat cure, since readings rise as the resin hardens.

A coating that protects primarily by impermeability, isolating the substrate from water, oxygen and dissolved ions rather than by galvanic or inhibitive action. High build epoxies and coatings pigmented with lamellar materials such as micaceous iron oxide or glass flake are typical examples.

A mineral fibre drawn from molten basalt rock, similar in handling and processing to glass fibre. It offers good temperature and chemical resistance, with mechanical properties generally described as sitting between E-glass and S-glass, and it is promoted as a lower impact alternative to glass in some applications, including concrete reinforcement.

In multi-coat finishing systems, notably automotive painting, the pigmented coat that provides the colour and visual effects such as metallic or pearlescent flake. It is normally protected by a clear topcoat that supplies gloss and durability.

The ability to trace a material or product back through its production history, linking finished items to raw material batches, process records and test results via batch or lot numbers. It is required by aerospace and marine quality systems and increasingly expected in construction supply chains, enabling targeted recalls and failure investigation.

A stitched, non crimp reinforcement with two fibre layers at set orientations, most commonly plus and minus 45 degrees or 0 and 90 degrees. The layers are held together by a fine stitching yarn rather than interlaced, so the fibres stay straight and translate their properties efficiently into the laminate.

A resin in which some or all of the petrochemical feedstock is replaced with material derived from renewable biological sources such as plant oils or sugars. Bio-based epoxies and polyesters are increasingly offered for composites and coatings to reduce embodied carbon, with the bio-based content declared as a proportion of the formulation.

A coating defect in which local loss of adhesion produces dome shaped, fluid filled or hollow raised areas in the film. Common causes include osmotic attraction of water to soluble salts trapped under the coating, retained solvent and application over contaminated surfaces.

A flat roof designed to attenuate rainfall by temporarily storing water on the roof and releasing it at a controlled rate through restricted outlets, reducing peak loads on drains and watercourses. Blue roofs form part of sustainable drainage (SuDS) strategies and place high demands on the reliability of the waterproofing and the structure.

A tubular or flat reinforcement made by interlacing yarns in a helical pattern, typically as a biaxial or triaxial braid. Braids conform well to curved and tapering geometry and are commonly used to overbraid cores and mandrels for tubes, struts and other slender components.

A textile process in which fibre tows are interlaced by rotating carriers to form tubular or flat preforms, often applied directly over a mandrel or core. Braided preforms offer good torsional properties and damage tolerance and are used for shafts, tubes and structural nodes.

A non-woven synthetic felt placed over the release film inside a vacuum bag to maintain a continuous air path across the whole part, so that vacuum is drawn evenly, and to absorb any resin that bleeds through. It is discarded after cure.

A vapour-permeable but water-resistant membrane used on the cold side of insulation, typically as a pitched roof underlay or behind cladding, allowing water vapour to escape from the construction while resisting liquid water from outside.

A UK-originated environmental assessment and certification scheme for buildings and infrastructure (Building Research Establishment Environmental Assessment Method), rating performance across areas such as energy, materials, water, waste and ecology. Product-level evidence such as environmental product declarations and responsible sourcing certification can contribute to a project's assessment.

The tendency of a material to fracture with little or no plastic deformation, as seen in glass and many cured thermosets. Brittle materials are sensitive to flaws, notches and impact, and fail suddenly rather than yielding.

A classification for the external fire performance of roof coverings under EN 13501-5, based on test 4 of CEN/TS 1187, the test method used in the UK. It indicates that the covering resists fire penetration and spread when exposed to external sources such as burning brands, and UK building regulations use it as the benchmark for unrestricted use of roof coverings.

The long-standing British Standard series for fire tests on building materials and structures, including surface spread of flame (Part 7), fire propagation (Part 6) and external fire exposure of roofs (Part 3). It has largely been superseded in UK regulation by the European EN 13501 classifications, but is still referenced in older specifications and certificates.

Sudden sideways instability of a slender or thin-walled element under compressive load, occurring at stresses that can be far below the material's strength. Resistance to buckling depends on stiffness and geometry, which is one reason sandwich construction is used to stabilise thin composite skins.

A dough-like moulding compound of short chopped fibres, filler and thermosetting resin, shaped by compression or injection moulding. BMC suits complex, detailed parts such as electrical housings, reflectors and valve components.

A two-dimensional plan-view map of a component produced by ultrasonic scanning, in which signal amplitude or time of flight is plotted over the scanned area. It is the standard output of automated composite inspection, showing the size and position of delaminations, voids and inclusions at a glance.

A continuous process in which heated rollers squeeze a polymer or rubber compound into sheet of closely controlled thickness. It is widely used to produce single-ply roofing and waterproofing membranes, including EPDM and PVC sheet, as well as many industrial rubber products.

A reinforcement fibre produced by carbonising a precursor, most commonly polyacrylonitrile (PAN) or pitch, to give continuous filaments composed largely of carbon. It offers very high stiffness and strength for its weight and is the principal reinforcement in high performance composites. Grades are commonly described by modulus class, such as standard, intermediate and high modulus.

A composite of carbon fibre in a polymer matrix, usually epoxy, offering very high stiffness and strength for low weight. CFRP is used for primary aircraft structure, motorsport chassis, wind turbine spar caps and bonded strengthening plates for existing buildings and bridges.

The total greenhouse gas emissions caused directly and indirectly by a product, organisation, activity or service, expressed as carbon dioxide equivalent. Product carbon footprints are normally calculated using life cycle assessment methods over a defined system boundary.

A substance that initiates or speeds a resin's curing reaction without being consumed in stoichiometric amounts. In the GRP trade the organic peroxide added to polyester resin, usually MEKP, is called the catalyst, although strictly it acts as an initiator.

An electrochemical technique for controlling corrosion by making the metal structure the cathode of an electrochemical cell, using either sacrificial anodes or an impressed current system. It is widely combined with protective coatings on pipelines, ships, jetties and offshore structures.

A rigid or semi-rigid plate placed over a laminate inside the vacuum bag to smooth the bag-side surface, spread consolidation pressure evenly and control local thickness. Caul plates are common in prepreg and infusion work where a good finish is needed on both faces.

A marking declaring that a product meets the applicable European Union legislation; for construction products it means performance has been assessed and declared against a harmonised European standard under the Construction Products Regulation. It is affixed by the manufacturer and supported by a Declaration of Performance and, where required, third-party assessment by a notified body.

An independent organisation, usually accredited by a national accreditation service, that assesses products, management systems or personnel against standards and issues certificates of conformity. Third-party certification gives specifiers confidence beyond a manufacturer's own declaration of performance.

A coating defect in which ultraviolet degradation of the binder at the surface leaves a loosely bound, powdery layer of pigment that can be rubbed off. It is a normal long term weathering mode of many exterior coatings and is more pronounced in binders with poor ultraviolet resistance.

A pendulum impact test in which a notched or unnotched bar specimen, supported at both ends, is struck by a swinging hammer and the energy absorbed in fracture is measured. It is used to compare the toughness of plastics, composites and metals; the plastics version is standardised in ISO 179.

Recycling that breaks polymers down into monomers, oligomers or other chemical feedstocks, for example by solvolysis or pyrolysis, so that new polymer can be made or embedded fibres recovered. It is a key route for reclaiming carbon fibre from manufacturing waste and end-of-life composite components.

A non woven glass reinforcement made from chopped strands distributed randomly and held with a powder or emulsion binder that dissolves in styrene based resins. It gives roughly equal in plane properties in all directions, wets out readily by hand lay up and is the standard reinforcement in GRP flat roofing laminates. It is specified by areal weight.

Glass fibre strands cut to short, controlled lengths for compounding into thermoplastics, for bulk and dough moulding compounds, or for chopping with resin in spray up laminating. The sizing applied to the strands is matched to the target polymer to promote adhesion and dispersion.

An economic model that keeps products and materials in use for as long as possible through reuse, repair, remanufacture and recycling, in contrast to the linear take, make, dispose model. In materials specification it drives requirements for recycled content, design for disassembly and credible end-of-life routes.

The highest standard of visible exterior surface finish, a term used mainly in the automotive industry to denote panels free from waviness, print-through and defects when inspected under critical lighting. Achieving it in composites drives choices such as tooling quality, low-shrink resin systems and surfacing films.

A recycling system in which material recovered from a product is reprocessed into the same or an equivalent product, retaining its quality and value. It contrasts with open-loop routes, where recovered material enters a different and often lower-grade application.

A joining method in which an uncured laminate is cured directly against a previously cured component, usually with an adhesive layer at the interface. It sits between co-curing and secondary bonding, and surface preparation of the cured element is critical to joint quality.

The curing of two or more elements, such as skins and stiffeners, in a single cure cycle so that they bond together as the resin cures, without a separate adhesive joint. It removes secondary assembly steps but demands careful tooling to control the geometry of all elements at once.

A layer of material applied to a substrate to protect it, decorate it or give it specific functional properties. In protective applications the coating is the main barrier against corrosion, weathering, chemical attack and abrasion, and is usually built up as a system of primer, intermediate and finish coats.

The fractional change in a material's dimensions per degree of temperature change. Mismatched expansion between joined materials, for example a composite bonded to aluminium, generates thermal stresses and distortion that must be allowed for in design.

Failure of a bonded joint within the body of the adhesive itself, leaving adhesive on both substrates, as opposed to adhesive failure at the interface. In joint testing it is generally the preferred failure mode, because it shows the bond to each substrate was stronger than the adhesive, so the adhesive's full capability was realised.

A continuous, factory controlled process in which paint is roller applied to coiled metal strip, cured in ovens and rewound before the strip is cut and formed into components. It is the basis of pre-finished steel and aluminium sheet used for roofing, cladding and rainwater goods.

A roof construction in which the insulation is placed at ceiling level below the structural deck, leaving the deck and the void above it at close to external temperature. The void normally requires ventilation to remove moisture vapour, and this arrangement is discouraged for flat roofs in current UK guidance because of condensation risk.

A material made from two or more constituents with distinct properties that remain identifiable in the finished material, most commonly a fibre reinforcement embedded in a polymer matrix. The combination delivers properties, such as high stiffness and strength at low weight, that neither constituent achieves alone.

A mode of loading that shortens or squeezes a material. Compressive behaviour often limits composite structures because thin skins can buckle and fibres can microbuckle at stresses well below their tensile capability.

A composite damage-tolerance test in which a laminate panel is first subjected to a controlled impact and then loaded in compression to failure to measure its retained strength. It matters because barely visible impact damage can markedly reduce compressive strength; ASTM D7137 is a widely used method.

A moulding process in which a charge of material, such as sheet moulding compound or a preheated thermoplastic blank, is placed in a heated matched metal mould and formed under press pressure. It offers short cycle times and good surface finish and is widely used for automotive panels and electrical components.

The application of pressure, with or without heat, to compact a laminate, bring the plies into intimate contact and drive out entrapped air. Adequate consolidation is essential to achieving the design fibre volume fraction and low void content.

A non woven reinforcement formed from continuous glass strands laid in a swirled pattern and bound into a mat. Because the fibres are continuous, the mat tolerates some flow and deep drawing during moulding, making it common in resin transfer moulding, pultrusion and glass mat thermoplastics.

A process in which resin, reinforcement and surface films are combined between moving carrier films and cured in-line as a continuous flat or profiled sheet. It is the method by which translucent GRP rooflight sheeting and flat GRP panel stock are produced.

Compressive collapse of a sandwich core, occurring either in service under concentrated loads or as a manufacturing defect when autoclave or press pressure drives the core inwards, typically at chamfered panel edges. It leaves a dished or wrinkled panel and reduces the structure's load-carrying capability.

The mass per unit volume of a core material, used as the primary grade designation for structural foams and honeycombs. Higher densities generally bring higher strength and stiffness at the cost of weight, so cores are specified by density alongside thickness and cell or grain structure.

The lightweight central layer of a sandwich construction, bonded between two thin, stiff face sheets to raise a panel's bending stiffness with minimal added weight. Common structural cores include polymer foams, honeycombs, end-grain balsa and syntactic materials, each specified by density, thickness and shear properties.

The shear loading carried by the core of a sandwich panel as it bends, transferring load between the two face sheets. Core shear strength and shear modulus are primary selection properties for core materials, and core shear failure is a common design-limiting mode in sandwich structures.

A foaming structural adhesive, commonly epoxy based and supplied as a film or paste, used to join sections of honeycomb or foam core edge to edge and to fill gaps between core and edge members. On heating it expands to fill the joint before curing, restoring load transfer across the splice.

A chemical species that reduces the corrosion rate of a metal when present in relatively small amounts, either dosed into the surrounding environment, for example in cooling water systems, or incorporated as inhibitive pigments within a primer.

A classification of the corrosivity of an atmospheric environment towards steel and zinc, defined in ISO 12944 and ISO 9223 as categories C1 to C5 plus CX for extreme environments, with separate categories for immersed conditions. It is the starting point for selecting a protective coating system and its target durability.

Mechanical or physical testing of small standardised specimens, known as coupons, cut from a laminate, panel or production sample rather than testing the full component. Coupon results underpin material qualification, design allowables and batch quality control in composites manufacture.

A life cycle assessment boundary covering raw material extraction through to the point where the product leaves the factory gate, excluding transport to site, installation, use and end-of-life. In construction EPDs to EN 15804 this corresponds to the product stage, modules A1 to A3.

A life cycle assessment boundary covering the full life of a product, from raw material extraction through manufacture, distribution and use to final disposal. It contrasts with cradle to gate, which stops at the factory, and with cradle to cradle approaches in which materials are recovered into new products instead of being disposed of.

Slow, time-dependent deformation of a material under sustained load. Polymers and adhesives creep far more readily than metals, particularly at elevated temperature or as the glass transition temperature is approached, so long-term loads must be assessed separately from short-term strength.

Long-duration testing in which a constant load or stress is applied to a specimen, usually at controlled temperature, while the slow time-dependent deformation is recorded. It is particularly important for polymers, adhesives and membranes, where deformation under sustained load can govern long-term design.

The waviness introduced into fibres where yarns pass over and under each other in a woven fabric. Crimp reduces the stiffness and compressive strength the fibres can deliver, which is why non-crimp fabrics and unidirectional tapes are preferred for highly loaded laminates.

A quick coating adhesion test in which a lattice of cuts is scribed through the coating to the substrate, adhesive tape is applied and removed, and the amount of coating detached is rated against a standard scale. It is standardised in ISO 2409 and ASTM D3359 and is best suited to relatively thin coatings.

The formation of chemical bonds between polymer chains, tying them into a three-dimensional network. It is the reaction underlying thermoset cure and determines rigidity, chemical resistance and the inability of cured resins to be re-melted.

The degree to which a polymer's molecular chains pack into ordered, crystalline regions. Higher crystallinity generally increases stiffness, chemical resistance and melting point but also raises moulding shrinkage, as in semi-crystalline thermoplastics such as polypropylene and PEEK.

The chemical process by which a liquid resin or adhesive hardens into its final solid state through crosslinking, driven by a hardener, catalyst, heat, moisture or radiation depending on the chemistry. Full properties develop only when cure is complete, which can take considerably longer than the initial set.

The programmed schedule of temperature, pressure and vacuum against time under which a thermosetting laminate or adhesive is cured, including heating ramps, dwells and cool-down. The cycle is defined in the material's processing data and qualified for the specific part and process.

Corrosion that develops at the exposed cut edges of pre-coated steel roof sheets, typically at overlaps and eaves, where the steel core is not protected by the factory coating system. It appears as coating delamination and rust creeping back from the edge, and is treated by preparation and application of edge protection coatings before it spreads into the sheet.

A single-part adhesive that polymerises very rapidly at room temperature when pressed into a thin film between surfaces, triggered by trace moisture on the substrates. It suits small, close-fitting parts in plastics, rubber and metal; limited gap filling and modest peel and impact performance restrict its structural use.

Intermediate vacuum compaction of a partially completed prepreg stack, carried out periodically during lay-up to remove trapped air and seat the plies before further layers are added. Regular debulks reduce wrinkling, bridging and final void content, especially on curved tooling.

The formal document a manufacturer must issue for a construction product covered by a harmonised European standard, declaring the product's essential characteristics and the performance values or classes it achieves. Drawing up a DoP is a legal prerequisite for CE marking under the Construction Products Regulation.

The removal of dissolved and entrained air from mixed liquid resin, usually by holding it under vacuum until bubbling subsides, before infusion or casting. Degassing reduces void formation and is particularly important for clear castings and high-performance infusions.

Separation of the plies within a laminate, caused by impact, manufacturing defects, fatigue or moisture ingress. Because it can spread unseen beneath an undamaged surface and sharply reduces compressive strength, delamination is a primary target of non-destructive inspection.

The progressive extension of an existing delamination between the plies of a laminate under cyclic or sustained loading. It is a central concern in damage-tolerant design of laminated structures and is characterised using interlaminar fracture toughness testing.

The removal of a cured or solidified part from its mould, using wedges, compressed air or mechanical ejection. Poor demoulding practice is a major source of gel coat damage, mould wear and part distortion.

A traditional unit of linear density equal to the mass in grams of nine thousand metres of fibre or yarn, still widely used for synthetic textile fibres such as polyester and aramid. It appears alongside the metric tex system in reinforcement specifications, one tex being equal to nine denier.

The mass of a material per unit volume. Density drives weight-critical design decisions and, combined with mechanical properties, determines the specific strength and stiffness on which composites compete with metals.

Designing products and buildings so that components can be separated non-destructively at end-of-life for reuse, remanufacture or high-grade recycling, for example by favouring mechanical fixings over permanent adhesive bonds. It is a core enabler of circular economy approaches in construction and manufacturing.

A thermal analysis technique that measures heat flow into or out of a small sample as it is heated, cooled or held at constant temperature. For thermosets it reveals the glass transition temperature, residual exotherm and degree of cure; for thermoplastics it shows melting and crystallisation behaviour.

A separation at a bonded interface, such as within an adhesive joint or between the skin and core of a sandwich panel. Disbonds may originate in manufacture or grow in service, and are detected by tap testing or ultrasonic inspection.

Recycling in which the recovered material is of lower quality or value than the original, so it can only be used in less demanding applications. Mixed glass fibre composite waste, for example, is often downcycled into filler or aggregate rather than new structural laminate.

A vertical pipe conveying rainwater from a roof outlet or gutter down to the drainage system at ground level. Downpipes are made from cast iron, steel, aluminium or plastics, and their number and size are determined by roof catchment area and design rainfall intensity.

The ability of a reinforcement fabric or prepreg to conform to a curved or double-curved mould surface without wrinkling or bridging. Weave style, fibre type and binder all affect drape, which is assessed when selecting materials for complex geometry.

A detail at a roof edge or gutter that projects the waterproofing beyond the supporting construction so water drips clear rather than tracking back under the covering. In felt roofing a welted drip turns the membrane down into the gutter, while preformed metal or GRP trims perform the same function in other systems.

The thickness of a coating measured after it has dried or cured, usually specified per coat and for the complete system. It is a key quality control parameter, checked non-destructively on metal substrates with magnetic induction or eddy current gauges.

An area of a moulding where resin has failed to wet out the reinforcement, leaving exposed or whitish fibre. Dry spots are a characteristic defect of resin infusion and wet layup, and act as sites for moisture ingress and delamination.

The capacity of a material to undergo significant permanent deformation before fracture, as displayed by most metals and many thermoplastics. Ductile behaviour gives visible warning of overload and allows local stresses to redistribute.

A corrosion protection system in which hot-dip galvanised steel is overcoated with paint or powder coating. The organic coating protects the zinc and the zinc protects the steel at any damage, so a well designed duplex system generally lasts longer than either coating used alone.

A thermal analysis technique that applies a small oscillating deformation to a specimen while temperature or frequency is varied, measuring storage modulus, loss modulus and tan delta. It is a sensitive method for determining the glass transition temperature and degree of cure of resins, adhesives and composites, and is also used on bituminous and polymeric roofing materials.

A boron free modification of E-glass formulated for improved resistance to acids and general corrosion. It is specified for chemical plant, pipes, tanks and other aggressive environments where standard E-glass may degrade, and is covered alongside E-glass in ASTM D578.

The standard general purpose grade of glass fibre, originally developed for electrical insulation applications, hence the E designation. It accounts for the great majority of glass reinforcement used in composites and its composition is defined in standards such as ASTM D578.

The lower horizontal edge of a roof slope, usually projecting beyond the wall face, where rainwater is discharged into the gutter. Eaves details typically include the fascia, soffit, ventilation openings and underlay support to prevent water being trapped behind the gutter.

A coating that cures to a flexible, rubber-like film capable of bridging fine cracks and accommodating movement of the substrate. Acrylic, polyurethane and silicone based elastomeric coatings are widely used for liquid applied roof waterproofing and for the refurbishment of profiled metal roofs.

An immersion painting process in which electrically charged paint particles deposit onto a conductive component under an applied voltage, producing a uniform film that reaches recesses and box sections. It is the standard priming process for car bodies and is also used on many industrial components.

A non-destructive survey method that finds breaches in roofing and waterproofing membranes by applying a voltage across the membrane and locating points where current passes through to a conductive substrate or wet deck. Low-voltage and high-voltage variants exist, and both pinpoint defects far more precisely than flood testing.

The strain at which a specimen ruptures in a tensile test, expressed as a percentage of its original length. High values indicate a ductile or flexible material such as an elastomeric roofing membrane, while rigid laminates typically fail at low elongation.

The greenhouse gas emissions associated with producing a material or product, covering raw material extraction, processing, manufacture and transport, and in whole-building assessments also construction, maintenance and end-of-life stages. It is expressed as carbon dioxide equivalent and is commonly reported through environmental product declarations.

The European standard series for the fire classification of construction products and building elements. Part 1 covers reaction to fire (the Euroclass system), Part 2 covers fire resistance, and Part 5 covers the external fire performance of roofs, giving classifications such as Broof(t4).

European Standards produced by the European standardisation bodies and adopted identically by national standards institutes, appearing in the UK as BS EN standards. Harmonised ENs under the Construction Products Regulation define how construction products, including roofing membranes and insulation, are tested, classified and CE marked.

Balsa core in which the wood grain runs perpendicular to the panel faces, so loads are carried along the strong axis of the timber's cells. This orientation gives far higher compressive and shear properties than flat-grain timber and is the standard form of balsa for structural sandwich cores.

The stage in a product's life cycle when it is removed from service and must be reused, recycled, recovered or disposed of. End-of-life scenarios are a required consideration in life cycle assessment and increasingly influence material selection for composites and roofing systems.

Recovering the energy content of waste that cannot practically be recycled, typically by incineration with heat and power generation or by co-processing in cement kilns, where composite waste can also contribute mineral content to the clinker. In the waste hierarchy it sits above landfill but below reuse and recycling.

An independently verified document that reports the environmental impacts of a product, based on a life cycle assessment carried out to agreed product category rules. For construction products, EPDs are typically produced to EN 15804, giving specifiers comparable data on embodied carbon and other impact categories.

Ethylene propylene diene monomer (M class) rubber, a synthetic elastomer with excellent resistance to ultraviolet light, ozone and weathering. In roofing it is used as a single-ply waterproofing membrane, often supplied in large prefabricated sheets, and it is also widely used for seals, gaskets, hoses and glazing profiles in the automotive, marine and industrial sectors.

A thermosetting resin based on molecules containing epoxide groups, cured by reaction with a hardener such as an amine or anhydride. Valued for strong adhesion, low cure shrinkage, chemical resistance and high mechanical performance, it is widely used in structural adhesives, laminating resins, coatings and composite matrices.

The harmonised European classification of construction products' reaction to fire under EN 13501-1, running from A1 (non-combustible) through A2, B, C, D and E to F, with supplementary classes for smoke production (s) and flaming droplets (d). UK building regulations reference Euroclass ratings for cladding, insulation and internal linings.

The heat released by a thermosetting resin as it cures. In thick sections or large mixed volumes the temperature rise can be severe enough to cause discolouration, cracking or degradation, so laminate thickness per pass and mixing quantities are managed to control it.

The thin, stiff outer layer bonded to each side of a sandwich core, typically a fibre-reinforced laminate or a metal sheet. Face sheets carry the in-plane tensile and compressive loads generated when the panel bends, while the core separates them and carries the shear.

The designed slope built into a nominally flat roof so that rainwater drains towards gutters or outlets. Falls may be formed by the structure, screeds, firring pieces or tapered insulation, and design gradients are normally set steeper than the minimum finished fall to allow for construction tolerances and deflection.

A board or profile fixed vertically at the roof edge, typically to the ends of the rafters, closing the eaves and usually carrying the rainwater gutter. Fascias are made from timber, cellular PVC, fibre cement or metal.

Progressive, localised damage caused by repeated or fluctuating loads at stresses below a material's static strength. Fatigue governs the life of components such as wind turbine blades, hulls and airframes, and typically initiates at stress concentrations.

Testing in which a specimen or component is subjected to repeated cyclic loading to establish how many cycles it survives at given stress or strain levels, with results often presented as S-N curves. It underpins life prediction for structures exposed to vibration, wind, wave and traffic loading.

A laminate of alternating thin metal sheets, usually aluminium alloy, and fibre-reinforced polymer layers bonded together. Fibre-metal laminates combine the fatigue and damage resistance of composites with the durability and inspectability of metal, and are used in aircraft fuselage skins.

The umbrella term for composites in which fibres such as glass, carbon, aramid or basalt reinforce a polymer matrix. In construction the abbreviation FRP commonly covers pultruded profiles, reinforcing bar and externally bonded strengthening systems.

The proportion of a composite's volume occupied by fibre, a key measure of laminate quality and the main driver of stiffness and strength in the fibre direction. It is determined by methods such as resin burn-off, acid digestion or image analysis of polished sections.

Deviation of fibres from their intended straight path, either in the plane of the ply or as out-of-plane wrinkles, introduced during layup, forming or cure. Waviness locally reduces compressive strength and is a significant quality concern in thick laminates such as wind blade spar caps.

A single continuous fibre, the basic unit from which strands, tows, yarns and rovings are built up. Filament diameter influences handling, wet out and the strength of the finished reinforcement.

A process in which continuous fibre tows, wetted with resin or pre-impregnated, are wound under tension onto a rotating mandrel in controlled patterns and then cured. It is the standard method for pressure vessels, pipes, tanks and other axisymmetric structures.

A particulate material blended into a resin, adhesive or sealant to modify its properties or reduce cost, for example calcium carbonate for bulk, fumed silica for thixotropy, or hollow microspheres for lightweight fairing compounds. Fillers also help control shrinkage, exotherm and sag.

The ability of a complete building element such as a wall, floor or door to withstand a fully developed fire for a stated period while maintaining loadbearing capacity, integrity and insulation (the R, E and I criteria). It is assessed by furnace testing and classified under EN 13501-2, and is distinct from reaction to fire, which concerns surface burning behaviour.

A strip of impervious material, traditionally lead but also aluminium, zinc, copper or polymeric products, dressed over joints and junctions such as upstands, abutments and chimneys to shed water over the waterproofing below. Cover flashings are typically let into masonry chases and dressed down over membrane upstands.

A roof with a very low pitch, in UK practice generally taken as no more than 10 degrees to the horizontal. Flat roofs rely on a continuous waterproof covering rather than overlapping units, and must be laid to falls so that rainwater drains to outlets.

A bast fibre extracted from the stem of the flax plant, the most established natural fibre for structural composite use. It is supplied as rovings, unidirectional tapes and woven or stitched fabrics, and is valued for its low density, vibration damping and renewable European sourcing.

A test in which a beam specimen is loaded in bending, usually in a three-point or four-point arrangement, to determine flexural strength and flexural modulus. Common methods include ISO 178 and ASTM D790 for plastics and ISO 14125 for fibre-reinforced composites.

An open mesh layer placed over or within a dry fibre stack during resin infusion to create a fast path for resin to spread across the part before wetting through the thickness. It is normally removed together with the peel ply after cure.

A gelcoat formulated with a wax additive so that its surface cures fully in air, applied by brush or roller as the final coat on GRP surfaces laminated against an open face rather than a mould. It is the standard topcoat on GRP flat roofs and on site-laminated linings and repairs.

A material's resistance to the propagation of a crack from an existing flaw. It underpins damage-tolerant design, and in laminates the related interlaminar fracture toughness describes resistance to delamination growth.

A thermosetting epoxy powder coating applied electrostatically to preheated steel, on which it melts, flows and cures to form a continuous film. It is a standard factory applied coating for buried and subsea pipelines and for corrosion protected reinforcing bar.

Accelerated corrosion of the less noble material when two dissimilar conductors are electrically connected in an electrolyte such as seawater. Carbon fibre composites in contact with aluminium or steel can drive galvanic attack, so joints are isolated with sealants, coatings or an insulating glass ply.

The time taken for a mixed resin to change from a workable liquid to a soft gel that can no longer be applied or moved. It marks the practical end of the working period and is quoted by resin suppliers at a stated temperature and catalyst addition.

A pigmented, resin-rich surface coat applied to the mould face before laminating, which cures to form the smooth, weather-resistant outer surface of a GRP moulding. It protects the underlying laminate from moisture and UV exposure and provides the colour and gloss of the finished part.

Fibre drawn from molten glass, the most widely used reinforcement for polymer composites. Different formulations, such as E-glass, E-CR glass, S-glass and AR glass, balance cost, strength, electrical performance and chemical resistance. It is the standard reinforcement in GRP laminates, including liquid applied GRP flat roofing systems.

A semi-finished sheet of glass mat reinforcement in a thermoplastic matrix, typically polypropylene, which is heated and compression moulded into parts in short cycle times. GMT is an established material for automotive components such as underbody shields, seat structures and bumper beams.

A composite of glass fibre reinforcement in a polymer matrix, most commonly polyester or vinyl ester resin. GRP is widely specified for boat hulls, tanks, enclosures, cladding and cold-applied flat roofing thanks to its corrosion resistance, mouldability and moderate cost.

The temperature region over which an amorphous or partly amorphous polymer changes from a rigid, glassy state to a softer, rubbery one. It sets a practical upper service temperature for resins and adhesives and can be reduced by absorbed moisture or incomplete cure.

A measure of how much heat a greenhouse gas traps in the atmosphere over a set time period relative to carbon dioxide, allowing emissions of different gases to be expressed as a single carbon dioxide equivalent figure. GWP is the headline indicator in most environmental product declarations and carbon footprint studies.

A roof deliberately covered with growing medium and vegetation over a waterproofing system, usually incorporating root barrier, drainage and filter layers. Extensive green roofs use shallow substrates with low-maintenance planting such as sedum, while intensive green roofs support deeper, landscaped schemes. They contribute to rainwater attenuation, biodiversity and reduced urban heat island effect.

A cold-applied roof waterproofing system in which glass fibre reinforcement, usually chopped strand mat, is laminated in situ with catalysed unsaturated polyester resin over a suitable deck, then finished with a pigmented topcoat. It produces a seamless, rigid covering commonly used on domestic flat roofs, valley gutters and preformed edge trims.

A channel that collects rainwater run-off from a roof and conveys it to outlets and downpipes. Gutters may be eaves-mounted, formed as valley or parapet gutters within the roof, or integrated into metal roofing systems, and are sized by rainfall calculation.

An open-mould process in which layers of dry reinforcement are placed in the mould by hand and wetted out with liquid resin using brushes and rollers before curing, usually at ambient temperature. It is the simplest and most widely used method of producing GRP laminates, including site-applied GRP roofing.

The component of a two-part resin or adhesive system that reacts chemically with the base resin to build the cured polymer network. Unlike a catalyst it is consumed in the reaction and must be dosed at the manufacturer's stated mix ratio; amines and anhydrides are common hardeners for epoxies.

The resistance of a material's surface to localised deformation such as indentation or scratching. Different scales suit different materials, with Shore used for elastomers and flexible membranes, Barcol for cured laminates and gelcoats, and Rockwell, Brinell or Vickers for metals.

The temperature at which a standard plastic bar deflects by a specified amount under a defined bending load while being heated at a set rate, measured to ISO 75 or ASTM D648. It is used to compare the short-term temperature resistance of resins and compounds, but it is not a safe continuous service temperature.

A discontinuity in a protective coating, such as a pinhole, void, crack or excessively thin spot, that exposes the substrate to the environment. Holidays are located with low voltage wet sponge or high voltage spark test instruments, particularly on pipeline coatings and tank linings.

A core material formed from thin walls arranged into an array of hexagonal or similar cells, used on edge between face sheets so the cell walls carry compression and shear. It offers very high stiffness and strength for its weight, with common types made from aluminium foil, resin-coated aramid paper and thermoplastics.

The joining of thermoplastic sheets or membranes by softening the mating faces with hot air and pressing them together with a roller, producing a homogeneous welded seam without adhesives or open flame. It is the standard seaming method for PVC and TPO single-ply roofing.

The process of coating steel or iron with zinc by immersion in a bath of molten zinc, forming metallurgically bonded zinc-iron alloy layers with an outer zinc surface. The coating protects both as a barrier and sacrificially, continuing to protect the steel at small areas of damage.

A composite combining two or more fibre types, such as carbon with glass or aramid, either mixed within a single fabric or as separate plies in one laminate. Hybridisation is used to balance cost, stiffness, impact tolerance and failure behaviour.

Chemical degradation caused by reaction with water, which breaks susceptible bonds such as the ester linkages in polyesters and some polyurethanes. Warm, humid conditions accelerate hydrolysis, which can degrade laminates, adhesives and membrane reinforcements over time.

The tendency of a material to absorb moisture from its surroundings. Moisture uptake in polymers and composites adds weight, plasticises the matrix and lowers the glass transition temperature, which is why laminates and adhesives are conditioned or dried before critical use.

A non-destructive method that uses an infrared camera to map surface temperature, revealing subsurface defects, trapped moisture or thermal bridges by their effect on heat flow. Active thermography with controlled heating is used on composites to find disbonds and impact damage, while passive surveys are widely used to locate wet insulation in flat roofs.

A chemical added in small amounts to a reactive resin to delay the onset of cure, extending shelf life and working time and protecting against premature gelation in storage or transport. Adjusting inhibitor level is one of the ways manufacturers tune the gel time of polyester and vinyl ester resins.

A high-volume process in which molten polymer, often short-fibre reinforced, is injected under high pressure into a closed metal mould, solidified and ejected. It provides tight tolerances and complex geometry at low unit cost once tooling costs are recovered.

The shear strength between the plies of a laminate, usually measured with a short beam shear test such as ISO 14130 or ASTM D2344. Low ILSS indicates poor fibre-to-matrix bonding or laminate quality, and correlates with susceptibility to delamination.

Condensation that occurs within the layers of a roof, wall or floor construction rather than on its internal surface, when water vapour moving through the build-up reaches a plane at or below its dew point temperature. It can degrade insulation, corrode fixings and decay timber, and is controlled through vapour control layers, ventilation and correct layer sequencing.

A passive fire protection coating that reacts to heat by swelling into a thick, insulating char, slowing the rate at which the protected substrate, typically structural steel, loses strength in a fire. Thin film and thick film systems are applied in buildings, offshore installations and industrial plant.

A flat roof arrangement in which moisture-resistant insulation, typically extruded polystyrene, is laid above the waterproofing membrane and held down by ballast or paving. The membrane is protected from thermal cycling, ultraviolet exposure and mechanical damage, but the insulation must tolerate contact with water.

Standards published by the International Organization for Standardization, the worldwide federation of national standards bodies. ISO test methods, such as the ISO 527 tensile series and ISO 14125 flexural method for composites, are widely cited on material datasheets, alongside management system standards such as ISO 9001.

The highly reactive chemical group that combines with polyols to form polyurethane, and with atmospheric moisture in one-part moisture-curing products. Isocyanates such as MDI and TDI are respiratory sensitisers, so spraying and heating polyurethane products are subject to strict workplace exposure controls.

The condition in which a material has the same properties in every direction, as with most metals, unreinforced plastics and glass. Isotropic behaviour simplifies design because a single set of property values applies regardless of load direction.

A pendulum impact test in which a notched specimen is clamped vertically as a cantilever and struck by a swinging hammer, with the energy absorbed in breaking it recorded as a measure of toughness. The plastics versions are standardised in ISO 180 and ASTM D256.

A raised frame or upstand constructed on a roof to support and weather items such as rooflights, smoke vents and plant, lifting them above the waterproofing plane. The membrane is dressed up the kerb and the unit itself or a flashing caps the top edge.

A composite element built up from multiple bonded layers (plies) of reinforcement and matrix, consolidated and cured so that they act as a single structural material. Its stiffness and strength depend on the fibre orientations and stacking sequence of the plies.

Redirecting waste away from landfill into reuse, recycling or energy recovery routes. Diversion rates are widely used as a sustainability metric for sites and projects, including in construction site waste management planning.

An adhesive bond test in which two overlapping substrates bonded over a defined area are pulled in tension, loading the joint in shear until failure. It is the most common way to compare structural adhesive performance on representative substrates, with methods including EN 1465, ISO 4587 and ASTM D1002.

The process of placing reinforcement plies into or onto a mould in the specified sequence and orientation, by hand or by machine; also used as a noun for the resulting stack or its design. Hand layup with wet resin remains the basic process for GRP boat building and GRP roofing.

Leadership in Energy and Environmental Design, a US-originated green building rating system used internationally, certifying projects at Certified, Silver, Gold and Platinum levels. Like BREEAM, it rewards product transparency measures such as environmental product declarations and strategies that reduce heat island effects.

A standardised method, set out in ISO 14040 and ISO 14044, for quantifying the environmental impacts of a product or system across its life, from raw material extraction through manufacture and use to end-of-life. LCA results underpin environmental product declarations and embodied carbon calculations used in material selection.

Waterproofing formed in situ by applying a liquid resin, typically polyurethane, polymethyl methacrylate (PMMA), unsaturated polyester or a bitumen-based formulation, by roller, brush or spray, which cures to a seamless elastomeric membrane. Often reinforced locally or throughout with a fleece, it is particularly suited to complex details and refurbishment over existing coverings.

A dense, voidless waterproofing material composed of graded limestone aggregate bound with bitumen, heated and applied in molten form by hand float to roofs, balconies, tanking and flooring. It sets to a seamless surface and has a long history of use in UK construction.

Recycling by physical processes such as shredding, grinding and re-melting or re-compounding, without breaking the polymer down chemically. Thermoplastics can often be re-melted into new products, whereas thermoset composites typically yield ground filler or short fibre fractions for lower-grade uses.

The overlap between adjacent sheets of roofing membrane or underlay where they are joined and sealed, by heat welding, solvent welding, adhesive, tape or bitumen bonding depending on the material. Lap integrity determines the watertightness of sheet systems, so minimum lap widths and the staggering of end laps are specified in system guidance.

An organic peroxide used as the initiator, commonly called the catalyst, for curing unsaturated polyester and vinyl ester resins at room temperature. It is corrosive and a strong oxidiser, requiring careful handling, storage away from accelerators, and accurate dosing to control gel time.

A two-part structural acrylic adhesive based on methyl methacrylate monomer, cured by a free-radical reaction between resin and activator. MMAs bond metals, composites and many plastics with minimal surface preparation and combine high strength with toughness, making them popular for bonding GRP structures and vehicle assemblies.

A naturally occurring lamellar form of iron oxide used as a flake pigment in intermediate and finish coats of heavy duty protective paints. The overlapping flakes align parallel to the surface, lengthening the path for moisture penetration and shielding the binder from ultraviolet light.

The proportion of resin to hardener, by weight or by volume, specified by the manufacturer for a two-part system. Because the components react stoichiometrically, deviating from the stated ratio leaves unreacted material in the joint and permanently degrades the cure; it must never be used as a way to speed or slow curing.

A curing mechanism in which a one-part adhesive, sealant or coating reacts with atmospheric humidity, hardening from the exposed surface inwards. One-part polyurethanes, silicones and silane-modified polymers cure this way; cure through thick sections is slow and depends on humidity and temperature.

A structure in which the outer skin carries the principal loads, rather than an internal frame. Composite monocoques, such as racing car survival cells and performance yacht hulls, are typically moulded as carbon fibre sandwich shells.

A small, reactive molecule that joins with others to form a polymer. In unsaturated polyester resins, for example, styrene monomer acts both as a diluent and as the cross-linking agent that reacts during cure.

A wax, semi-permanent polymer or film applied to tool surfaces so that cured parts release cleanly without damage to the part or the mould. Correct application routines are essential, and transfer of release agent onto surfaces intended for bonding or painting is a common cause of adhesion failures.

A stitched reinforcement in which two or more layers of fibres at different orientations, as in biaxial, triaxial and quadraxial constructions, are combined in a single fabric. It allows several plies to be laid in one operation, cutting layup time on large structures such as wind turbine blades and boat hulls.

A composite reinforced with plant-derived fibres such as flax, hemp or jute in a thermoset or thermoplastic matrix. Natural fibres offer low density and lower embodied carbon than glass fibre, at the cost of greater moisture sensitivity and more variable mechanical properties.

Plant derived fibres such as flax, hemp, jute and sisal used to reinforce polymer composites. They offer low density, renewable sourcing and good vibration damping, at the cost of moisture sensitivity and greater property variability than synthetic fibres. They are established in automotive interior panels and are increasingly specified in marine, sporting and construction products.

A family of reinforcements in which straight, uncrimped layers of fibre are held together by stitching or bonding rather than by weaving. Avoiding crimp improves stiffness, strength and fatigue performance compared with equivalent woven fabrics, and the format suits automated handling and the infusion of large parts.

Inspection methods that assess the condition or internal quality of a material or component without damaging it, including ultrasonic, radiographic, thermographic, dye penetrant and acoustic emission techniques. It is essential for finding hidden defects such as delaminations, voids and disbonds in safety-critical structures.

A conformity assessment body designated by an EU member state and notified to the European Commission to carry out the third-party testing, inspection and certification tasks required by EU legislation, including those supporting CE marking. The UK equivalent under the UKCA regime is known as an approved body.

The period after an adhesive has been applied during which the parts can still be joined and a sound bond achieved. Once the open time is exceeded, through skinning, solvent loss or advancing cure, the surfaces no longer wet each other properly and the joint will be weak.

The greenhouse gas emissions arising from the use of a building or asset over its life, such as the energy consumed for heating, cooling, lighting and equipment. It is distinguished from embodied carbon; as buildings become more energy efficient, embodied carbon accounts for a growing share of whole-life emissions.

A fully consolidated sheet of continuous fibre fabric in a thermoplastic matrix, supplied ready to be heated and thermoformed, often with injection-moulded ribs added in the same tool. Organosheets bring continuous-fibre performance to high-volume automotive production.

A material with different properties along three mutually perpendicular axes, such as a unidirectional composite ply or timber. Orthotropic behaviour is a well-defined special case of anisotropy and underpins classical laminate analysis.

The movement of water through a semi-permeable layer towards a more concentrated solution. In glass fibre hulls, water diffusing through the gelcoat can react with soluble substances in the laminate to form fluid-filled blisters, a defect widely known in the marine industry as osmosis or osmotic blistering.

Blistering of gelcoated GRP laminates after prolonged water immersion, caused by water diffusing through the gelcoat and forming concentrated solutions in small voids, which then draw in more water by osmosis. It is most familiar on boat hulls below the waterline.

Composite manufacturing routes that achieve low-void laminates without autoclave pressure, typically using vacuum-bag-only prepregs, oven cure or resin infusion. It reduces capital and energy costs and removes the part size limits imposed by autoclave dimensions.

Refurbishment of an existing roof by installing a new waterproofing or covering system over the retained build-up rather than stripping it, normally after a condition survey and condensation risk assessment. On profiled metal roofs the equivalent practice is called oversheeting, where new sheets are fixed over the old covering on spacer systems.

Degradation caused by reaction with oxygen, which embrittles polymers and bituminous compounds and corrodes metals. Heat and sunlight accelerate oxidative ageing, so antioxidants and protective coatings are used to prolong service life.

A low wall extending above the roof line at the edge of a roof, balcony or bridge. Parapets require careful waterproofing, with membrane upstands, damp proof courses and copings, because they are exposed on both faces and are a common source of water ingress.

The formation of a thin, stable oxide film on a metal surface that markedly reduces its chemical reactivity, occurring naturally on metals such as stainless steel and aluminium or induced deliberately by chemical treatment. Passivation treatments for stainless steel remove free iron contamination and restore the protective chromium rich oxide layer.

A sacrificial woven fabric laminated onto the surface of a laminate and torn off after cure, leaving a clean, uniformly textured surface ready for bonding or painting. Release-coated variants can transfer contamination and are generally avoided where structural bonding will follow.

A test that measures the force needed to progressively separate a bonded joint or laminated layer by peeling, usually at a defined angle such as 90 or 180 degrees. It is used on adhesives, coatings, laminates and roofing membrane seams, where peel loading is typically the weakest mode of a bond.

Closed-cell thermoplastic polyester foam used as a structural sandwich core. It is thermoformable, recyclable and often manufactured with recycled content, and its fatigue and processing performance has made it a common choice in wind turbine blades and transport structures.

A thermosetting resin made from phenol and formaldehyde, notable for excellent fire performance with low smoke and toxic gas emission. It is used for composite panels in aircraft and rail interiors, decorative and industrial laminates, foundry binders and adhesives where fire, smoke and toxicity requirements govern material choice.

The simplest weave style, in which each warp yarn passes alternately over and under each weft yarn. It is stable and easy to handle but has the highest crimp of the common weave styles, which slightly reduces mechanical performance and limits drape over complex curvature.

A thick, usually embossed coating based on PVC dispersed in plasticiser, applied by coil coating over primed, galvanised steel used for profiled roofing and cladding sheets. It offers good formability and durability, but cut edges and mechanical damage need maintenance to prevent edge corrosion and peel back.

A full-size master shape, machined or hand built to the finished part geometry, from which production moulds are laminated. Plug surface quality is critical because every defect transfers first to the mould and then to each part made from it.

A single layer of reinforcement within a laminate, such as one sheet of prepreg, fabric or unidirectional tape. Plies are stacked at specified orientations to give the finished laminate its required directional properties.

The ratio of lateral contraction to axial extension when a material is stretched. It describes how a material thins as it is pulled and is needed alongside the elastic moduli for stress analysis, particularly in laminate calculations.

A rigid closed-cell foam chemically related to polyurethane but with a higher proportion of isocyanurate linkages, which improves fire performance and thermal stability. It is widely used as the insulation core of flat roof boards and metal-faced cladding and roofing panels.

A large molecule built from many repeating chemical units joined into long chains. Polymers include thermoplastics, thermosets and elastomers, and form the matrices, adhesives, coatings and membranes used throughout the materials industry.

Bitumen blended with polymers, most commonly styrene butadiene styrene (SBS) for elastomeric flexibility or atactic polypropylene (APP) for plastomeric heat resistance, to improve low-temperature flexibility, fatigue resistance and durability compared with unmodified bitumen. It is used in roofing membranes and also as a binder in road surfacing.

An acrylic polymer supplied both as a transparent thermoplastic sheet (acrylic glass) and as a fast-curing reactive resin. In liquid-applied roof waterproofing and industrial flooring, PMMA resins cure rapidly by peroxide-initiated polymerisation, including in cool conditions, allowing quick return to service.

A broad polymer family formed by reacting isocyanates with polyols, producing everything from soft foams and elastomers to rigid plastics, adhesives, sealants and coatings. In construction and roofing it appears as insulation foam, liquid-applied waterproofing membranes and flexible adhesives, and many one-part grades cure with ambient moisture.

A cellular polymer produced by reacting polyols with isocyanates, available in rigid closed-cell grades for insulation and core applications and in flexible grades for cushioning. Rigid PU foam is used as the insulating core of composite building panels and as a sandwich core where structural demands are modest, and spray-applied forms are used in roofing and cavity insulation.

Rainwater that remains standing on a flat roof after the rest of the surface has drained, typically caused by inadequate falls, structural deflection or blocked outlets. Persistent ponding adds load, accelerates deterioration of some coverings and can invalidate system guarantees.

A controlled period at elevated temperature applied after a resin has initially hardened, driving the crosslinking reaction closer to completion. Post-curing raises the glass transition temperature and improves mechanical and chemical properties, and is routine for epoxy laminates and structural bonded assemblies.

The length of time a mixed, reactive resin or adhesive remains usable in the mixing vessel before it thickens beyond application. Pot life shortens as temperature and mixed quantity increase, because the curing reaction generates its own heat.

A dry finishing process in which electrostatically charged powder, commonly polyester, epoxy or hybrid chemistry, is sprayed onto an earthed component and then fused and cured in an oven to form a continuous film. The process is essentially solvent free and allows overspray to be recovered and reused.

Reinforcement fibre pre-impregnated with a controlled quantity of resin, usually a partially cured (B-staged) thermoset, supplied in rolls and stored chilled or frozen until layup. Prepregs give precise fibre and resin content and are the standard material form for high-performance aerospace and motorsport laminates.

The manufacture of composite parts from reinforcement pre-impregnated with a controlled amount of partially cured resin. Plies are cut, laid into a mould and debulked, then consolidated and cured under heat and pressure, typically in an autoclave or oven, giving very consistent fibre and resin content.

A preparatory coating applied to a substrate before an adhesive, sealant, coating or waterproofing membrane, improving adhesion by sealing porosity, binding dust or providing a chemically compatible surface. Primer selection depends on both the substrate and the product to be applied over it.

A surface defect in which the pattern of the underlying reinforcement or core becomes visible on the finished face of a moulding, usually as a result of resin shrinkage during cure or post-cure. It is a particular concern on high-gloss gelcoated and painted panels.

Steel or aluminium sheet cold roll-formed into trapezoidal, sinusoidal or other profiles to provide spanning stiffness, used as roof and wall cladding and as structural decking. Sheets are typically metallic-coated steel with a factory-applied organic coating, fixed through to purlins or rails, or used as the skins of built-up and composite panel systems.

A test in which a metal dolly is glued to a coating or applied layer and pulled off perpendicular to the surface with a calibrated instrument, recording the tensile stress at detachment and the failure mode. Standardised in ISO 4624 and ASTM D4541, it is widely used on site to verify the adhesion of coatings, screeds and liquid-applied membranes.

A continuous process in which fibre reinforcement is drawn through a resin bath and a heated die, curing into a constant cross-section profile such as a rod, tube or structural section. It gives very high fibre alignment along the pull direction and suits long production runs.

A horizontal secondary structural member spanning between principal rafters, portal frames or walls, supporting the roof cladding or decking. In modern industrial buildings purlins are commonly cold roll-formed galvanised steel sections such as zed and cee profiles; in traditional construction they are timber.

Closed-cell polyvinyl chloride foam supplied in sheet form as a structural sandwich core. Crosslinked grades offer higher stiffness and temperature resistance, while linear grades are tougher and more ductile; both are widely used in boat hulls and decks, wind turbine blades and vehicle panels.

A single-ply roofing and waterproofing sheet based on plasticised polyvinyl chloride, usually reinforced with a polyester or glass fibre scrim and joined by hot-air welded seams. PVC membranes are flexible and easy to detail, though plasticiser migration and incompatibility with bitumen and polystyrene must be addressed in design, typically with separation layers.

A coil or spray applied architectural coating based on polyvinylidene fluoride resin, valued for outstanding colour and gloss retention and resistance to ultraviolet light and chemical attack. It is commonly specified for premium metal roofing, cladding and curtain walling.

A laminate with equal numbers of plies in three or more equally spaced orientations, giving in-plane stiffness that is effectively the same in every direction. It is the standard conservative layup where load directions are uncertain or vary in service.

A non-destructive method that passes X-rays or gamma rays through a component onto a detector, so that internal features and defects appear as density variations in the image. It is used on welds, castings and bonded or composite assemblies, and computed tomography variants provide full three-dimensional views.

The drainage fitting through which water leaves a flat roof or gutter into the downpipe system, incorporating a clamped or welded connection to the waterproofing and usually a leaf guard or grating. Outlets are positioned at the low points of the falls, with secondary overflow provision to guard against blockage.

The regulatory framework for the Registration, Evaluation, Authorisation and Restriction of Chemicals, operating as EU REACH and, since Brexit, a parallel UK REACH regime. It governs which substances may be used in products such as resins, hardeners and coatings, and requires suppliers to communicate the presence of substances of very high concern through the supply chain.

How a material or product behaves as a fuel in the early stages of a fire, covering ignitability, flame spread, heat release and smoke production. It is distinct from fire resistance, which concerns how long a complete construction element withstands a developed fire; in Europe reaction to fire is classified under EN 13501-1.

Material recovered from waste and reprocessed into a raw material for manufacturing, such as polymer granulate produced from post-consumer or post-industrial plastic. The quality and consistency of recyclate determine whether it can substitute virgin material in demanding applications.

Carbon fibre reclaimed from manufacturing waste or end-of-life components, usually by pyrolysis or solvolysis, and supplied in chopped, milled or nonwoven mat forms. It is generally shorter and less consistent than virgin fibre, so it suits nonstructural and semi-structural applications where full aerospace-grade properties are not required.

The proportion of a product, by mass, made from recycled rather than virgin material, usually split into post-consumer content (from products discarded after use) and pre-consumer or post-industrial content (from manufacturing waste). Definitions and self-declared claims are commonly made with reference to ISO 14021.

A sheet waterproofing material comprising a polyester or glass fibre carrier coated with oxidised or polymer-modified bitumen, normally installed in two or more bonded layers on flat roofs. It is the modern UK term for what was traditionally called built-up felt roofing.

A thin polymer film, often perforated, placed between the laminate and the breather in a vacuum bag stack. It prevents the breather bonding to the part, while the perforation pattern controls how much resin is allowed to bleed out during cure.

Stress locked into a material or assembly in the absence of external load, arising from cure shrinkage, thermal mismatch during cooling, welding or forming. Residual stresses cause distortion, such as spring-in of composite parts, and can add to service stresses to promote cracking.

A closed-mould process in which dry reinforcement is laid into a mould, sealed under a vacuum bag, and liquid resin is drawn through the fibre stack by vacuum alone. It achieves higher fibre content and lower void levels than open moulding, with much lower workshop emissions.

A closed-mould process in which a dry fibre preform is placed in a matched mould and liquid resin is injected under pressure before curing. It produces parts with two moulded faces, good dimensional control and repeatable quality at medium to high volumes.

A vessel placed in the vacuum line between the mould and the pump during infusion or wet bagging to intercept surplus resin before it can reach and damage the vacuum pump.

Managing the procurement of materials so that supply chains meet defined environmental, social and ethical standards. In UK construction it is commonly demonstrated through certification to BES 6001 for construction products, or through chain of custody schemes such as FSC and PEFC for timber.

The horizontal line at the apex of a pitched roof where two slopes meet, closed with ridge tiles, a formed metal capping or a ventilated ridge system. The detail must weather the junction of the meeting coverings and often provides high-level ventilation to the roof space.

The structural layer of a flat or low-pitched roof that supports the waterproofing build-up and imposed loads, commonly profiled steel, timber boarding, plywood, oriented strand board, or in-situ or precast concrete. The deck type influences fixing methods, falls, deflection and condensation behaviour.

Any element that passes through the roof waterproofing, such as soil vent pipes, flues, cables, plant supports and drainage outlets. Each penetration must be individually sealed, typically with upstands, sleeves, preformed collars or liquid-applied detailing, and penetrations are a leading location for leaks.

A glazed unit installed in a roof to admit daylight, ranging from domed and flat glass units mounted on kerbs on flat roofs to in-plane translucent sheets in profiled metal roofing. Key considerations include thermal performance, fire rating, non-fragility classification and the waterproofing detail at the kerb or laps.

A bundle of parallel, untwisted glass fibre strands wound onto a cylindrical package. Direct rovings feed processes such as filament winding, pultrusion and weaving, while assembled (multi end) rovings are designed for chopping in spray up; rovings are specified by tex and by sizing type.

A high strength grade of glass fibre based on a magnesium aluminosilicate composition, offering greater tensile strength and stiffness than E-glass. It is specified where performance justifies its higher cost, notably in aerospace, defence and demanding industrial applications. The comparable European family is generally designated R-glass.

A block of a more electrochemically active metal, commonly a zinc, aluminium or magnesium alloy, electrically connected to a structure so that it corrodes preferentially and protects the structure. Anodes are consumed in service and are inspected and replaced as part of planned maintenance.

An accelerated laboratory corrosion test in which coated or plated specimens are exposed to a fine fog of salt solution in a closed chamber under standardised conditions, as described in ISO 9227 and ASTM B117. Results are used for comparative and quality control purposes, as correlation with service life in real atmospheres is limited.

Closed-cell styrene acrylonitrile foam used as a structural sandwich core, valued for its high toughness and elongation combined with good static strength. Its damage tolerance has made it popular for boat hulls and other impact-prone sandwich structures.

A composite construction in which two thin, stiff skins are bonded to a thick, lightweight core such as foam, honeycomb or balsa. Separating the skins raises bending stiffness dramatically for very little added weight.

A low crimp weave style in which each warp yarn floats over several weft yarns before interlacing, described by its harness number, for example four harness or eight harness satin. It offers excellent drape and surface smoothness at the cost of a less stable, asymmetric fabric that requires care in handling and lay up.

Core sheet cut with a grid of slits or kerfs, often combined with a scrim backing, so that it can conform to curved mould surfaces. The cuts also act as channels for resin flow during infusion, although they increase resin uptake and therefore the finished weight of the panel.

A lightweight open-weave fabric used as a flexible carrier or stabiliser. In core materials it is bonded to one face of small core blocks so the sheet can drape over curved moulds, while in roofing membranes and coated fabrics a scrim acts as the reinforcing carrier that gives the sheet dimensional stability and tear resistance.

A flexible material applied to joints and interfaces to exclude water, air or other media while accommodating movement between the parts, in contrast to an adhesive whose primary job is to transfer load. Silicone, polyurethane, polysulphide and silane-modified polymer chemistries dominate construction and industrial sealing.

The adhesive joining of two or more fully cured composite or metallic parts in a separate operation after moulding. Joint performance depends heavily on surface preparation, adhesive selection and control of bondline thickness.

A mode of loading in which adjacent planes of a material slide relative to one another, as in an adhesive lap joint or between the plies of a laminate. Shear properties often govern the design of bonded joints and sandwich cores.

The upright laminate member joining the spar caps inside a wind turbine blade or similar beam-like structure, transferring shear between them so the assembly behaves as an I-beam. Shear webs are commonly sandwich panels bonded in place with structural adhesive.

A ready-to-mould sheet of chopped glass or carbon fibre, mineral filler and thermosetting resin, compression moulded under heat and pressure into stiff parts with good surface finish. SMC is widely used for vehicle body panels, electrical enclosures and building components.

The hardness of rubbers, elastomers and softer plastics measured with a durometer that presses a spring-loaded indenter into the surface, most commonly on the Shore A scale for elastomers and Shore D for harder materials. Methods are standardised in ASTM D2240 and related ISO standards.

An adhesive and sealant chemistry based on polymer chains terminated with silane groups that crosslink with atmospheric moisture, combining the flexibility and weather resistance of silicones with the paintability and cleaner handling of polyurethanes, and containing no isocyanates. Widely used for elastic bonding and sealing in construction, marine deck fitting and vehicle assembly.

A polymer family with a backbone of alternating silicon and oxygen atoms, giving outstanding resistance to weathering, UV and temperature extremes while remaining flexible. Silicones are used as sealants, gaskets, mould-making rubbers and liquid-applied roof coatings, and most sealant grades cure at room temperature with atmospheric moisture.

A factory-manufactured polymeric waterproofing sheet, typically EPDM, TPO or PVC, installed in a single layer and joined at laps by welding, adhesive or tape. Single-ply systems may be mechanically fastened, fully adhered or ballasted, and are widely used on flat and low-pitched roofs.

A thin surface treatment applied to fibres during manufacture, typically containing film formers, coupling agents such as silanes, and processing aids. It protects the filaments during handling and, critically, controls adhesion and compatibility between the fibre and the matrix resin, so it must be matched to the resin system in use.

The thin, stiff facing laminate on each side of a sandwich structure, carrying the in-plane and bending loads while the core carries shear. The term is also used more generally for the outer aerodynamic or weathering surface of a composite structure.

Loss of adhesion between a sandwich panel's face sheet and its core, arising from manufacturing defects, impact damage, moisture ingress or fatigue. It removes the shear connection the panel relies on and can grow under load, so debonds are a key target of non-destructive inspection.

The underside surface of a building element, most commonly the horizontal board closing the underside of the eaves overhang between the fascia and the wall, often ventilated to allow airflow into the roof void. The term is also used for the underside of slabs, arches and balconies.

The main unidirectional load-bearing element running along the length of a wind turbine blade or wing spar, carrying the principal bending loads. Spar caps are typically thick stacks of unidirectional glass or carbon laminate, or pre-cured pultruded planks bonded into the structure.

A material's strength divided by its density, commonly called the strength-to-weight ratio. High specific strength is the principal reason fibre-reinforced composites displace metals in weight-critical aerospace, motorsport and marine structures.

An open-mould process in which chopped glass fibre and catalysed resin are sprayed simultaneously onto a mould surface and then compacted with rollers. It is faster than hand lay-up and suits large parts, but gives less consistent fibre content and laminate thickness.

A fabric woven from tows that have been spread into thin, flat tapes before weaving, giving an ultra light reinforcement with very low crimp. The format reduces ply thickness and resin rich zones and is used where minimum weight matters, such as high performance marine, motorsport and aerospace structures.

The tendency of a cured composite angle or curved section to close slightly relative to the mould geometry, caused by the difference between in-plane and through-thickness thermal and cure shrinkage. Tooling is often compensated at the design stage to allow for it.

The specified order and orientation of the plies through the thickness of a laminate, usually written as a shorthand code of ply angles. It governs the laminate's stiffness, strength and coupling behaviour, and is fixed on the drawing as part of the laminate schedule.

A metal roofing system in which long sheets or trays of steel, aluminium, zinc or copper are joined by raised interlocking seams that stand proud of the drainage plane, with concealed clips that allow thermal movement. Suited to low pitches and long uninterrupted runs, standing seam roofs have no exposed through-fixings in the main roof area.

The resistance of a material or structure to elastic deformation under load, governed by the elastic modulus and by geometry. Stiffness is distinct from strength: a component can be stiff yet weak, or flexible yet strong, and the two must be considered separately in design.

The deformation of a material in response to stress, expressed as change in length divided by original length. Strain is dimensionless, often quoted as a percentage, and may be elastic (recoverable) or plastic (permanent).

The internal force carried by a material per unit of cross-sectional area. Stress may be tensile, compressive or shear, and comparing the applied stress with the material's strength is the basis of structural design.

A localised increase in stress around a geometric feature such as a hole, notch, sharp corner or ply drop. Stress concentrations are common initiation sites for fatigue cracks and are managed with generous radii, local reinforcement and careful detailing.

The gradual reduction in stress within a material held at constant strain, the counterpart of creep. It is important for gaskets, seals and bolted joints in polymers, where clamping loads can decay over time.

An additional coat of paint applied by brush or roller to welds, edges, corners, bolt heads and other irregular details where sprayed coatings tend to pull thin. Stripe coating is standard practice in high performance protective coating specifications.

An adhesive designed to carry significant service loads as part of an engineered joint, transferring stress between substrates over the whole bonded area rather than at discrete fasteners. Epoxies, polyurethanes and methacrylates are the main chemistries, used in applications from aircraft assemblies to wind turbine blade bonding.

A reactive monomer that acts as both diluent and crosslinking agent in unsaturated polyester and vinyl ester resins, copolymerising into the cured network rather than evaporating like a true solvent. Styrene content influences viscosity and shrinkage, and workplace exposure to styrene vapour is subject to occupational limits.

The surface onto which a coating, membrane, adhesive or covering is applied. In roofing this may be the structural deck, insulation, screed or an existing waterproofing layer; substrate condition, priming and compatibility govern adhesion and long-term performance.

A standardised description of the visual cleanliness of a steel surface before painting, defined in ISO 8501-1 as Sa grades for blast cleaned steel and St grades for hand and power tool cleaned steel. Coating specifications state the required preparation grade because coating life depends heavily on surface preparation.

The peak to valley roughness imparted to a substrate by abrasive blast cleaning, which provides a mechanical key for coating adhesion. The profile must be matched to the coating system and is measured using comparators, replica tape or stylus instruments.

A lightweight non woven tissue of fine glass or polyester fibres applied at the surface of a laminate. It supports a resin rich surface layer that improves finish, weathering and chemical resistance, and it is standard practice in corrosion barriers for chemical plant and in pultruded profiles.

Drainage designed to manage surface water close to where it falls, mimicking natural processes to reduce flood risk and pollution rather than piping runoff straight to sewers. Typical features include permeable surfaces, swales, attenuation storage and green or blue roofs.

A laminate whose ply orientations and materials mirror each other about the mid-plane. Symmetry prevents coupling between in-plane loads and bending, so the laminate remains flat after cure instead of warping.

A composite core material made by dispersing hollow microspheres, usually glass, in a resin matrix, producing a closed-cell material with high compressive strength and very low water absorption. It is used for deep-water buoyancy, as a core in highly loaded local areas, and as a machinable filler and insert material.

Rigid insulation boards manufactured or cut to a wedge profile and laid to a designed scheme to create drainage falls on a flat roof, avoiding the need for screeds or firrings. Schemes combine tapered and flat boards to achieve both the required fall and the target U-value.

The maximum tensile stress a material can withstand before failure, determined by pulling a specimen to rupture in a tensile test. It is one of the most widely quoted mechanical properties on datasheets for metals, plastics, laminates and membranes.

A mechanical test in which a specimen is pulled along its axis until it breaks, measuring properties such as tensile strength, tensile modulus and elongation at break. For plastics and composites it is commonly performed to methods in the ISO 527 series or ASTM D638 and D3039. It is the baseline test for characterising resins, laminates and reinforcement materials.

A mode of loading that stretches a material along its axis. Fibres such as carbon and glass are most efficient in tension, which is why laminates are orientated so that the fibres carry the principal tensile loads.

The metric unit of linear density for fibres, strands and yarns, defined as the mass in grams of one kilometre of the product. Glass rovings and yarns are specified by tex, with higher values indicating heavier strands.

Localised paths of increased heat flow through an insulated construction where a more conductive element, such as a metal fixing, rafter or parapet junction, bypasses the insulation. Thermal bridges increase heat loss and can produce cold internal surfaces that lead to condensation and mould growth.

The rate at which a material conducts heat. Polymers and cellular foams have low conductivity and act as insulators, while metals conduct readily, a contrast that matters in roof build-ups, battery enclosures and mould tooling.

A group of processes, including flame, arc and plasma spraying, in which metal or ceramic feedstock is melted or softened and propelled as fine particles onto a substrate to build up a coating. Thermally sprayed aluminium and zinc are used for long term corrosion protection of steel, while plasma sprayed ceramics provide wear and thermal barrier coatings.

A thermoplastic core material, such as PET foam or certain linear PVC foams, that can be softened with heat and formed to a curved shape before lamination. Thermoforming avoids the slits used in scored core, so the finished panel absorbs less resin and keeps a more uniform surface.

The forming of heated thermoplastic sheet over or into a mould using vacuum, air pressure or matched tooling, then cooling it to shape. Applications range from vacuum-formed cladding and rooflight components to the forming of consolidated thermoplastic composite blanks.

A thermal analysis technique that records the mass of a sample as it is heated under a controlled atmosphere, revealing decomposition temperatures, filler or fibre content and volatile content. It is often run alongside DSC to characterise polymers, resins and composite formulations.

A polymer that softens when heated and hardens again on cooling without chemical change, so it can be reshaped, welded or recycled. Thermoplastics range from commodity materials such as polypropylene and PVC to high-performance matrices such as PEEK used in advanced composites.

A composite whose matrix is a thermoplastic polymer, such as polypropylene, polyamide or PEEK, rather than a curing thermoset. Thermoplastic composites can be formed and reformed with heat, joined by welding rather than bonding, and are more readily recycled at end of life.

A polymer that cures irreversibly through crosslinking, forming a rigid three-dimensional network that cannot be re-melted or reshaped by heating. Epoxy, polyester, vinyl ester, phenolic and polyurethane resins are common thermosets used as composite matrices, adhesives and coatings.

The property of becoming thinner when stirred or sheared and recovering viscosity at rest. Thixotropic resins, gelcoats and adhesives can be brushed or spread easily yet resist sagging or draining on vertical surfaces; fumed silica is the usual thixotropic additive.

The moulds, mandrels, jigs and fixtures on and in which parts are laminated, formed and cured. Tooling material selection, from GRP and epoxy tooling board through to nickel alloy and steel, is driven by cure temperature, thermal expansion match, accuracy requirements and production volume.

The final coat of a coating system, providing the specified colour, gloss and resistance to weathering, ultraviolet light and chemical exposure. It is the system's first line of defence against the environment and largely determines how the finish looks over time.

A reinforced bitumen membrane applied by melting the underside of the sheet with a gas torch so that it bonds to the substrate or preceding layer as it is rolled out. Torch application requires strict hot-works controls, and flame-free alternatives such as self-adhesive membranes are often specified where fire risk must be eliminated.

A structural adhesive modified with a dispersed rubbery or thermoplastic phase that blunts cracks and absorbs fracture energy, improving peel and impact performance without a large sacrifice in strength or temperature resistance. Toughened epoxies and acrylics are standard for bonded joints subject to vibration, impact or peel loading.

The ability of a material to absorb energy and deform without fracturing, combining strength with ductility. Tough materials resist impact and flaw growth, whereas strong but brittle materials can fail suddenly.

A bundle of thousands of continuous carbon filaments handled as a single unit, the carbon fibre equivalent of a glass roving. Tows are designated by their filament count in thousands, written with a K, and are used directly in filament winding, automated fibre placement and weaving.

Thermoplastic polyolefin, a polymer blend based on polypropylene and ethylene propylene rubber, used as a heat-weldable single-ply roofing membrane. Being thermoplastic, seams are joined by hot-air welding rather than adhesive, and the material contains no plasticisers. Related grades are used for automotive interior and exterior components.

The removal of excess cured material, flash and rough edges from a moulded part to its final profile using hand tools, CNC routing or abrasive waterjet cutting. Composite trimming requires effective dust extraction and suitable cutters because glass and carbon laminates are highly abrasive.

A weave style in which warp yarns pass over and under two or more weft yarns in a staggered pattern, producing a characteristic diagonal rib. It drapes and conforms to curvature better than plain weave and has lower crimp, and the 2x2 twill is the most recognisable carbon fibre fabric style.

A coating supplied as two components, a base and a curing agent, that are mixed immediately before use and cure by chemical reaction rather than solely by solvent evaporation. Epoxy and polyurethane two-pack coatings dominate high performance protective and refinish work, and once mixed they must be applied within the pot life.

An adhesive or resin supplied as two separate components, typically a resin and a hardener, that begin to cure only once mixed. Two-part systems cure through the full depth of the joint without needing air or moisture, but demand accurate proportioning, thorough mixing and use within the pot life.

Certification that a product design meets a defined set of rules or standards, granted after review of documentation and testing of representative samples, so that subsequent production items are accepted without individual testing. It is common in the marine sector, where classification societies type approve materials and equipment, and in automotive regulation.

A measure of thermal transmittance, the rate of heat flow through unit area of a building element per unit temperature difference between inside and outside, expressed in watts per square metre kelvin. Lower U-values indicate better insulation, and limiting values for roofs and other elements are set by national building regulations.

A gel spun fibre of ultra high molecular weight polyethylene, offering exceptional strength for its weight together with very low moisture uptake and good chemical resistance. Its low surface energy makes bonding to resins difficult, and its use is limited by a low melting temperature and susceptibility to creep. Typical applications include ropes, slings, ballistic protection and impact resistant hybrid laminates.

The UK Conformity Assessed marking, introduced after the UK left the EU as the domestic equivalent of CE marking for goods placed on the market in Great Britain. Conformity is assessed against designated standards, with any required third-party work carried out by UK approved bodies; CE marking remains accepted for many product types under continuity arrangements.

A non-destructive method that sends high-frequency sound pulses into a material and analyses the reflected or transmitted signals to detect internal flaws and measure thickness. In composites it is the principal technique for finding delaminations, voids and disbonds, applied by pulse-echo or through-transmission scanning.

A reinforcement in which nearly all fibres run in a single direction, held together by light stitching, a binder or occasional weft threads. It delivers the highest stiffness and strength along the fibre axis and is used where loads are strongly directional, for example wind blade spar caps and bonded strengthening plates.

Reinforcement in which virtually all fibres run in a single direction, supplied as dry tape, lightly stitched or bound fabric, or prepreg. Unidirectional plies give the highest stiffness and strength along the fibre direction but need supporting plies in other orientations.

A thermosetting resin dissolved in a reactive monomer, usually styrene, that cures by free-radical polymerisation when initiated with an organic peroxide such as MEKP. It is the workhorse matrix for glass-reinforced plastic in boat building, GRP roofing, tanks and vehicle panels, offering low cost and straightforward processing.

The vertical or near-vertical continuation of the roof waterproofing above the general roof level at abutments, parapets, rooflight kerbs and penetrations. UK guidance calls for upstands of sufficient height above the finished roof surface, terminated with a flashing or capping so water cannot get behind the membrane.

The effect whereby built-up areas are noticeably warmer than the surrounding countryside, because dark, dense surfaces absorb and re-radiate solar energy while there is less vegetation and evaporative cooling. Roofing measures such as reflective cool roof surfaces and green roofs are used to mitigate it.

The breakdown of polymer surfaces by ultraviolet radiation, causing chalking, discolouration, embrittlement and loss of gloss. Exposed resins, membranes and coatings are protected with UV stabilisers, pigmented gelcoats or sacrificial surface layers.

An additive that protects polymers, coatings and sealants against degradation by ultraviolet light, either by absorbing the radiation (ultraviolet absorbers) or by scavenging the free radicals it generates (hindered amine light stabilisers). It is used to delay chalking, colour fade and embrittlement in exterior applications.

A variant of resin transfer moulding in which resin is drawn into dry reinforcement under vacuum, typically with a rigid mould face on one side and a flexible film or light shell on the other. The term is often used interchangeably with resin infusion, particularly in North American literature.

A tacky butyl rubber tape used to seal the vacuum bag film to the tool flange, or to itself, forming an airtight envelope around the laminate. Grades are chosen to match the cure temperature and to release cleanly from tooling afterwards.

A consolidation technique in which a laminate is sealed under a flexible airtight film and the air is evacuated so that atmospheric pressure compacts the plies during cure. It removes trapped air and excess resin and is used with wet lay-up, prepreg and infusion processes.

A membrane or sheet installed on the warm side of insulation to restrict the passage of water vapour from inside the building into the roof or wall construction, reducing the risk of interstitial condensation. Materials range from polyethylene sheet to bitumen membranes and foil composites, and effectiveness depends on sealed laps, edges and penetrations.

The edge of a pitched roof at a gable, where the roof covering meets or oversails the end wall. Verges are finished with mortar bedding, dry verge systems or bargeboards to close the covering against wind and rain.

A thermosetting resin made by reacting an epoxy resin with an unsaturated acid and dissolving the product in styrene; it processes like a polyester but offers better toughness, chemical resistance and resistance to hydrolysis. Commonly specified for boat hulls, chemical plant, tank linings and as a barrier layer against osmosis.

Material behaviour that combines viscous flow with elastic response, so that stiffness depends on time, loading rate and temperature. Polymers are viscoelastic, which gives rise to creep, stress relaxation and damping, and is characterised by dynamic mechanical analysis.

The proportion of a cured laminate's volume occupied by trapped air or volatiles rather than fibre or resin. Elevated void content degrades interlaminar shear strength and fatigue performance, so it is controlled through debulking, vacuum and cure pressure and checked by testing or non-destructive inspection.

Determination of the proportion of trapped air or volatiles within a cured laminate, typically by density comparison, matrix digestion or burn-off methods, or by image analysis of polished sections. Excess void content degrades interlaminar shear and fatigue performance, so limits are often specified for structural laminates.

An organic chemical that evaporates readily at ambient temperature, released from solvents in coatings, adhesives and resin systems; styrene emitted during open-mould polyester lamination is a well-known example in composites. VOC content and emissions are regulated in the UK and EU, driving the shift towards water-based, high-solids and low-styrene products.

The chemical crosslinking of rubber, traditionally with sulphur under heat and pressure, which converts a mouldable compound into a durable elastomer. Cured EPDM roofing membranes and many sealing profiles are vulcanised during manufacture.

A roof construction in which the thermal insulation is placed above the structural deck, keeping the deck and supporting structure at close to internal temperature. A vapour control layer is normally installed on the warm side of the insulation to limit the risk of interstitial condensation.

The two yarn directions in a woven fabric, with warp yarns running along the roll length and weft yarns running across it. Their balance governs the directional properties of the fabric, and the terms ends and picks describe the respective yarn counts.

A localised element of a roof or below-ground waterproofing system where the continuous field membrane is interrupted or terminated, such as upstands, penetrations, outlets, movement joints and edges. Details demand specific design and careful workmanship, and they are where most waterproofing failures originate.

The gradual change in the appearance and properties of a material caused by outdoor exposure to ultraviolet radiation, moisture, temperature cycling and airborne pollutants. Coating and material durability is assessed by natural exposure trials and by accelerated weathering tests in the laboratory.

The thickness of a coating film measured immediately after application, before solvent loss or curing, typically using a comb gauge. Together with the coating's volume solids it allows the applicator to predict and control the final dry film thickness.

The degree to which liquid resin has penetrated and coated the filaments of a reinforcement, visible in glass fabrics as a change from opaque white to translucent. Complete wet-out is essential to laminate strength, since dry patches act as built-in defects.

The ability of a liquid adhesive, resin or coating to spread over and make intimate contact with a substrate or fibre surface. Good wetting is essential for adhesion and for full fibre impregnation in composites, and depends on the relative surface energies of the liquid and substrate and on surface cleanliness.

The sum of embodied and operational carbon over the full life cycle of a building or asset, from raw material extraction through use to demolition and disposal. In the UK it is commonly assessed using RICS whole life carbon guidance, which aligns with the framework of EN 15978.

The suction force exerted on a roof by wind flowing over and around a building, greatest at perimeters and corners. Roof systems resist uplift through mechanical fastening, adhesion or ballast, with design loads derived from wind actions codes and system resistance established by testing.

Testing that establishes how well a roof assembly resists the suction loads generated by wind, typically by applying static or cyclic negative pressure to a full-scale roof specimen until failure or a target load is reached. Results support wind uplift calculations and fixing specifications for mechanically fastened, adhered and ballasted flat roof systems.

A heavy, coarse fabric woven directly from untwisted glass rovings, usually in a plain weave. It builds laminate thickness and directional strength quickly and is traditionally alternated with chopped strand mat in marine and industrial GRP laminates.

The stress at which a material begins to deform permanently rather than elastically. Loading beyond the yield point leaves residual deformation after unloading; many brittle materials, including cured thermoset laminates, fracture without showing a distinct yield.

A measure of a material's stiffness, defined as the ratio of stress to strain in the elastic region of loading. A higher modulus means less deflection under a given load; for plastics and composites it is typically measured in tension to ISO 527.

A primer containing a high loading of metallic zinc dust in an organic binder, usually epoxy, or an inorganic silicate binder, providing galvanic protection to steel in a similar way to galvanising. It requires a high standard of blast cleaned surface so that the zinc makes electrical contact with the steel.