Wet-out

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.

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.

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 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.

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 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.