Fixing a Fiberglass Fender
Fiberglass is a durable and lightweight material that’s easily repaired. The damaged fiberglass is replaced with layers of new fiberglass material that’s as thick as the surrounding fiberglass. Working with fiberglass can get messy, but it’s relatively easy to pick up.
1. Grind away damaged fiberglass with a die grinder. Once you have all the damaged and frayed fiberglass ground down, gradually taper the edges of the damage as far as possible.
2. Wipe down the surface of the repair, using a rag damp with acetone. Let the acetone completely dry.
3. Cover the back of the repair from the inside of the fender roller if it is a large hole, using thick plastic. Secure the plastic to the back of the repair, using spray glue. This will give the wet fiberglass repair support until it hardens.
4. Tear pieces of fiberglass mat the same size as the repair, using as many layers as it takes to build the fiberglass back up to its original thickness. Make each layer 1/4 inch larger than the last so the edge of the repair will gradually taper instead of forming a ledge.
5. Mix a batch of polyester resin in a small bucket, using 2 percent catalyst and a paint stirrer. Apply the smallest layer of mat to the center of the damage and saturate it with resin, using the felt roller. Roll out any trapped air bubbles, using an air roller. Let the fiberglass harden for two to three hours.
6. Mix a batch of fiberglass filler on a scrap piece of cardboard, using 2 percent catalyst. Work the catalyst into the filler so the mix is the consistency of putty. Apply a thin, even layer of filler over the fiberglass patch, using a putty knife. Let the filler harden for a few hours.
7. Sand the filler with 200-grit, then 400-grit sandpaper with the palm sander. The repair will be level with the surrounding fiberglass and should be invisible when painted.