Hand lay-up

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 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 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.

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.

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.