What is GRP

All you wanted to know about GRP but were afraid to ask

GRP stands for ‘Glassfibre Reinforced Plastics’, also referred to as ‘Fibreglass’, Composite Plastics, and in the USA, FRP. It is an amazingly versatile material, and one that is little understood in industry, but GRP has truly immense potential across a wide spectrum of applications.

Its vast range of properties can be confusing to the uninitiated. It is a ‘plastic’, but it displays few of the disadvantages of conventional ‘thermoplastics’ in everyday use.

For instance, it will not melt, but will burn in a similar way to wood, but can be easily and cheaply made fire-retardant. It is very strong – seven times the flexural strength of steel. GRP is very lightweight with the tremendous energy absorption properties which have made it a common material for racing cars and boats. Its finish is achieved in contact with a mould surface and takes on the precise texture of that mould. GRP can replicate the highest showroom gloss to the texture of cast iron, stone, or the finest grained wood. Colour choices are infinite, from the complete ranges of BS, RAL and Pantone to translucent, metallic and ‘glitter’ effects.

Bespoke GRP Mouldings

GRP is a moulded product which requires some sort of former or tool from which it is moulded. In its simplest and most common form, known as ‘hand-lay’, the mould is first prepared with a release wax, similar to car polish. The colour is then applied by brush or spray to the mould face as a ‘gelcoat’, which is a thickened, coloured resin. This is allowed to ‘cure’ for about 20-30 minutes and is followed by layers of glass fibre mat together with the resin. This can be put down or ‘layed-up’ by brush, or even sprayed using special machines which ‘chop’ continuous filaments of glass fibre into specified lengths and blow these down in a spray of resin. The product is then formed by the hardening of the resin and glass matrix into an integrated moulding.

The hardening agent is called the ‘catalyst’ which is mixed into the resin at precise formulations causing ‘exothermic’ heat to build up in the moulding. This cures the resin within a normal working time of 20-30 minutes. After about an hour the moulding can be lifted from the mould to be trimmed of excess material and finished as required.

Development in Creating GRP Mouldings

Over the years new technology has allowed much more sophisticated systems to offer far greater properties. Closed moulding now offers ‘good-both-sides’ mouldings and the use of ‘core’ materials between the glass fibre laminations has added immeasurably to strength and durability.

Techniques using translucent laminates can now ‘encapsulate’ graphics within the laminate both for protection and for backlit displays. Special masking techniques make multi-coloured and multitextured moulding possible.