Gelcoat

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 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.

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.

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.

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.