GRP Materials


Normally the outer finish of a GRP component is finished with Gelcoat, which is a modified resin and provides the colour to the surface of the product. The gelcoat, as well as improving the aesthetics, provides the GRP with good abrasion and weathering resistance. Gelcoat can be applied by spray or brush to the mould surface and it can be colour matched to a customer's specific requirement. Commonly we utilise the BS and RAL colour ranges.

Gelcoat can also used as a waterproof coating to the inside of a GRP component.


Glass fibres are the main reinforcements used in the GRP industry, hence the term fibreglass or glassfibre. Chopped Strand Mat is the most commonly used glass reinforcement. It is constructed of strands of glass about 45mm long held together in bundles of about 200 fibres called strands. The strands are randomly distributed and held together with a binder to form a mat, which is supplied in rolls. Another form of common glass reinforcement are Woven Rovings, which are long strands of glass woven into a cloth. Depending on which direction the required tensile strength is needed the cloth can be woven at different angles. It may also be combined with the Chopped Strand Mat to produce a product known as a Combination Mat.


A thermoset resin is used in GRP, which basically means setting under heat. To initiate the setting of the resin three basic chemicals are required: resin, a catalyst and an accelerator.

The catalyst is the initiator and the accelerator, as the name suggests, accelerates the reaction. Polyester resin is the main type of resin used in the GRP industry. This resin has good all-round properties for most moulding applications. Other resins include phenolic, which are used for their non-flammable properties, vinyl esters, which are used for their high laminate strength and resistance to water impregnation and epoxy resin, which is used for its high strength.

Glass Reinforced Plastic is used as it provides good strength to weight ratio when compared with other materials. Strength is determined by compression load, tensile load and stiffness. GRP gains its compression load from the resin used and the stiffness and tensile load from the fibres.

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