Explosive Plastic: GRP Car Bodies Make History

1993 TVR Cerbera

It’s gone by a variety of names over the years but name notwithstanding, the materials we are about to discuss are all essentially the same. Some call it fibreglass, the Americans call it fiberglass, others go the whole hog and call it glass reinforced plastic while many refer to it as GRP, a contraction of the last name.

When used for constructing car bodies, GRP has a number of significant advantages. Car bodies begin as a mock up, usually hand crafted in clay over a wooden armature, or skeleton. Translating such a shape into metal is a necessarily complicated and time-consuming process. A metal-bodied prototype will probably have hand beaten panels, made at a vast cost in time and effort. Taking the prototype from one-off to production status is still more costly. Metal press tools have to be made from scratch and over time, they have to be maintained.

Enter GRP. To make a car body out of this material is relatively simple and inexpensive. Using the mock up as the ‘buck’, a manufacturer can make a mould quite quickly and easily. Suitably reinforced, and made into sub sections as necessary, the mould can be used to produce exact copies of the buck. And this isn’t a one off – the mould can be used over and over again. Given these advantages, it’s no wonder that GRP allowed the spawning of a wide variety of interesting and exciting car bodies. What’s more, GRP car bodies can’t be dented and can’t corrode.

The Glasspar G2, manufactured by Bill Tritt in 1949, was the first sports car with an all GRP body built by an American manufacturer. It was built using methods that enjoyed a resurgence much later on, in the many kit and replica cars that appeared on the market. It used a Jeep chassis but one with a desirable extra in the shape of a highly modified V8 engine.

It wasn’t long before major manufacturers became wise to the benefits of GRP, especially as it was cheap and easier to work than sheet metal. These were ideal characteristics for the building of prototypes and low volume production cars.

The Chevrolet Corvette C1 appeared as a concept show car at the GM Motorama in 1953. Not long after, we in the UK became aware of a home-grown rival. The Daimler Dart, was later renamed the SP250, because US company Dodge had the rights to the name ‘Dart’. But the SP 250 debuted at the New York motor show in 1959, complete with GRP body.

It must be said now that the rest is history. One concern that carried the banner for GRP bodywork was Reliant, famed for the Del Boy Supervan and its successor, the Reliant Robin. The company is better respected for its Scimitar models, a long run of coupes and sports estate cars. The Scimitar ultimately became a two seat open sports car which, like its predecessors, was largely Ford-based.

Meanwhile, a number of other firms jumped on the GRP bandwagon, Lotus being one of the larger ones. But many smaller firms were attracted by the ease and relative cheapness of originating a brand-new body shape in GRP. Among them were Marcos, TVR, Ginetta, Gordon Keeble and Gilbern, all of which produced GRP bodied cars on a low volume production basis.

It’s an arguable point but it is probable that the emergence of kit cars in Britain was spearheaded by a film. More accurately, it was the appearance of a GRP bodied beach buggy – a rebodied VW Beetle – in the 1968 film ‘The Thomas Crown Affair’ that led to the appearance of a variety of kit cars, special cars and replicas in the UK.

In some instances, new GRP bodies, cladding simple tubular steel chassis, could be used to partly recycle existing cars. Quite a number of enthusiasts built such cars, based on Ford Escort or Cortina, or on Mini or VW mechanical parts. Replica cars generally had more desirable donors. Many a replica of an AC Shelby Cobra had steering, brakes and suspension courtesy of Jaguar, usually allied to a Rover V8 or one of its larger American brothers.

Meanwhile, GRP as a material was growing up. The use of flame retardant resins made life rather safer. Though it was be the case that a GRP bodied car was no harder to ignite than a conventional one, it was a different story if fire took hold. Flame retardant resins made the conversion of the bodywork into a large pile of blackened Shredded Wheat far less likely.

The bigger manufacturers were also making inroads into the development of new moulding techniques. Lotus and Reliant each adopted injection moulding methods, for example. They also began following major manufacturers by developing deformable bumper sections, designed to spring back after impact.

What had begun life as a material used for building boats, as well as fabricating a variety of other things, gained a new life as a car body building material. It is, of course, still in use today and it has developed still more. Carbon fibre construction works on essentially the same principle as GRP construction, with the glass strands’ role taken over by the carbon fibre mesh.

No story of this nature would be complete without mention of the inevitable oddball. Between 1973 and 1980, French engineering group Matra, in conjunction with car firm Simca, produced two sports models. In this context, it wasn’t the Matra Simca Bagheera and Murena’s having three seats abreast that made them odd. Many people believe, incorrectly, that these cars had GRP bodies. However the Bagheera especially made use of polyurethane for its bodywork; it was very like an Airfix kit, through its use of injection moulded plastic. Conversely, the Murena had a number of GRP panels, albeit ones produced by a hot pressure moulding technique.


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