Gorilla Hair is a fiberglass resin body filler that is used extensively in professional automotive collision repair. Fiberglass resin body filler is used to build deep dents which cannot be pulled with ordinary means, and is also used to repair damaged fiberglass bodies on vehicles such as Corvettes and boats. Gorilla Hair fiberglass resin is sold in gallon jugs with hardener resin included. The hardener must be mixed into the resin for the fiberglass to cure.
Affix the 80-grit sanding disc to the dual-action sander, then thoroughly clean the inside of the dent that is to be filled. The fiberglass resin will not stick to smooth surfaces, so be sure that the entire concave surface of the dent is roughed with the sanding disc.
Spread an appropriate amount of Gorilla Hair fiberglass resin onto the cardboard which will be the mixing board. Use as much resin as you feel is necessary to fill the dent. Knead the tube of resin hardener thoroughly to mix the contents, then apply a small amount of the hardener onto the top of the fiberglass resin. The rule of thumb is to use only between 1 percent and 5 percent hardener for the amount of resin you use. Too little hardener will cause the resin to remain unhardened, while too much will cause cracks in the finished product.
Mix the hardener and the fiberglass resin thoroughly with the paint stick. There should be no colored swirl marks in the resin. Ideally, it will be all one consistent color. Use the scraper/applicator to fold the mixture over itself several times to be certain that the mixture is complete.
Apply a heavy amount of the mixed resin to the dent being filled, pressing it with the applicator into the grooves cut by the sander. Smooth the resin out toward the edges of the dent from the center, working to smooth the fiberglass fibers down into the resin so that they completely fill the hole.
Allow the fiberglass resin to cure completely. The chemical reaction of the hardener and the resin will make the mixture get very warm. When this warmth has cooled to the touch, the resin can be sanded.
Sand the resin using the 80-grit sandpaper with the dual-action sander to smooth the highest edges of the resin in preparation for a skim coat of normal body filler.
