Fiberglass (GRP) is a type of plastic impregnated with small filaments of glass as reinforcement (it is also called glass reinforced plastic. It is a light material, resistant to both compression and tension and easy to mold into even complex shapes. first introduced by the aviation industry and has also gained popularity in the manufacture of car bodies, boat hulls and even residential construction. Its special features make grinding this material a bit complicated and learning the right technique requires a lot of preparatory work and patience.
Steps
Step 1. Let the fiberglass "mature" in the sun
If you have to work on a new component, there will be a thin layer of gelcoat on its surface. Gelcoat is an epoxy or resinous coating that is used to coat molds when making fiberglass parts. Before sanding, leave the piece in the sun for 2-7 days to cure the gelcoat. This allows all the air bubbles, which would create problems during grinding and painting, to evaporate.
Step 2. Assemble the components if possible
If your project requires multiple pieces (such as the bodywork, doors and hood of a car), mount them before grinding or finishing them. Thus the sandblasting work will be uniform from one component to another, creating a smooth and continuous surface.
Step 3. Clean all GRP with a degreaser and wax remover
This is an important step to eliminate any residual substance that is sprayed into the molds to facilitate the detachment of the fiberglass piece. You can find degreaser and wax remover at all auto parts stores.
Step 4. Sand the GRP with coarse sandpaper
For the first step, use an 80 or 100 grit. Attach the paper to a long emery pad to work large, flat surfaces. For smaller areas or areas with intricate curves and surfaces, use a rubber emery that follows the shapes better.
- Never sand through the entire gelcoat layer to fiberglass. This causes two problems: it weakens the material and creates holes in the GRP that would break the paint layer.
- The gelcoat should be used as a guide during the first step of blasting. You should work hard enough to make the coating opaque, so when all the components have lost their luster, it means that you have sanded enough to allow the primer and color to adhere.
Step 5. Fill any depression on the GRP surface
Make the surface homogeneous with specific putty. Put them on the concavities and then smooth to make everything smooth.
Step 6. Apply primer
When all of the GRP has been sanded with the coarse sandpaper, you can apply a coat of primer. Wait for it to dry. Do not use a mordant as it does not adhere well to fiberglass.
Step 7. Sand this time using fine grit sandpaper
When the primer is dry, sand the entire surface with 180 or 220 paper. You can then apply another coat of primer or go to the paint, remember to sand after each coat.
