Fibreglass is durable material used for many applications, one of the most common of which are fibreglass bumpers. Over time, though, the paint on bumpers can fade, requiring that they be repainted to look their best. Though the easiest solution is to have a bodyworks garage paint the bumpers, it can be done for less money with the right materials and knowledge.
Remove the bumpers from the car. This will make the painting easier, since you will be able to move the bumpers around and there will not be as much taping off to do. If the bumpers are still mounted on the car, use masking tape and newspaper to mask off surrounding areas so that they do not get overspray on them.
Clean the bumper with a mild degreaser or cleaner and then thoroughly dry the bumper.
Inspect the bumper closely for pin holes and/or cracks. Minor cracks can be filled in with Bondo. Small pinholes can be filled in with spot putty. Large cracks will have to be repaired properly with new fibreglass.
Apply the Bondo and or spot putty to the needed areas. Let the filler dry and then sand smooth with 220-grit sandpaper. Use a block with sandpaper on it to make sure there are no high and low spots. If there are, fill in the low spots and sand down the high spots.
Sand the entire bumper with 220-grit sandpaper.
Clean the bumper thoroughly with white spirit. This is an important step. The fibreglass needs to be completely clean and free of oils for proper paint adhesion.
Spray on a light coat of primer. Let the primer dry and then spray on a full coat. Sand the bumper with 220-grit and then 400-grit wet sandpaper once the primer is dry. Apply another one to three coats, wet sanding between coats.
Spray on a light coat of the colour that you have chosen for your bumper. Let the paint dry and then apply a heavier coat, spraying smoothly back and forth about eight to ten inches from the surface. Apply several coats, wet sanding in between with 220-grit and then 400-grit sandpaper.
Allow the paint to dry thoroughly, which may take as long as overnight.
Wet sand the paint using 220-grit, 400-grit, 600-grit and then 1200-grit sandpaper.
Buff the paint with a high-speed buffer. Use a rubbing compound, then a polishing compound and then finally a wax to finish the polishing. Be sure not to burn through the paint.
Reinstall the bumper or remove the masking tape and paper.
Have a store like NAPA Paints mix up a colour that matches the rest of the car and have them put the paint in a spray can. Bumper paint, which comes in a variety of finishes from flat to glossy black, can be found at auto parts stores.
Always use a proper face mask to protect your lungs and wear rubber gloves to avoid contact with fibreglass dust from sanding as well as the overspray from the paint that gets into the air.