Creating a car body from foam allows you to build a lightweight, inexpensive and unique body designed for use on a specific vehicle chassis. By using foam panels, you'll be able to quickly form the body, shaping it by hand in any way imaginable, and with a layer of fibreglass added onto the foam, your car body can be given the same level of finish as any other car, creating a sturdy and attractive body useful for anything from display to prototyping.
Create a car body frame using plywood forms, cut into the general body design size and shape. Attach the plywood directly to the car chassis using bolts. The plywood frame will act primarily as a support for the foam boards and should be cut only as general contours. Attach at least four forms to the chassis, one for each end of the car body, and one for each end of the seating compartment.
Place the foam boards over the plywood structure pieces, securing them to the wood using the adhesive. Cut the boards about 1 inch longer than necessary before placement, trimming the excess using a foam cutter, after the adhesive has set. Foam cutters are portable heated tools that quickly cut through the foam using heated wires. To build up the foam height for the car body, glue layers of panels together using the adhesive before placing them onto the plywood. The foam body panels should be one to two inches thicker than the desired body contours to allow for shaping of the foam. Begin with the larger car-length panels located at the centre of the car body, and work outward, placing smaller panels.
Detail the foam car body by shaping the foam using a sanding block. By running the block along the foam you can remove foam material, sculpting the ultimate shape of the car body.
Add details to the car body by adding additional foam panels to create areas such as wheel wells. These additions will need to be sanded to shape as well.
Place a layer of fibreglass cloth over fragile parts after shaping in order to reinforce them when completing the car body. Apply a layer of resin with a brush over the fibreglass for further support of the areas.
Cut lines into the foam body where needed for car body details, sanding the edges of the lines smooth using a hand file.
Apply two layers of six-ounce fibreglass cloth to the foam boards for extra strength and support, painting each layer with the resin. Cover all foam surfaces with the fibreglass coating.
Cut openings into the foam, such as windows or doors where required, through the fibreglass encased foam using a reciprocating saw. Apply layers of fibreglass cloth with resin to the cut edges.
Smooth the surface of the fibreglass body using a file to remove any fibreglass drips and surface ridges, and then cover the body with a plastic body filler such as Bondo, filing the filler down until you've created a smooth level car body surface. Remove file marks with a 36 grit sandpaper, and then create a smooth finish with a 100 grit sandpaper.
Spray the body with a polyester primer and then paint the car body the final colour desired.
Use a safety mask with a particle respirator when cutting the foam or sanding the fibreglass to avoid breathing hazardous particles.