Auto Body Fiberglass Repair
Repair to a small amount of damage on a fiberglass bodywork is a task capable of accomplishment with little talent or experience. First the amount of damage must be assessed to determine the method to be used. The easiest to repair is a very minor scape or scratch that does not fully break or create a major crack in the body panel. The second more difficult would find a portion of the fiberglass missing, broken away or a larger crack.
Both degrees of damage requires sanding away the paint and primer to the fiberglass layer. Always sand 1 to 2 inches beyond the damage area until no further cracking of the fiberglass work if apparent. Crazing or spider cracks occur in fiberglass bodywork and will eventually show through if not fully repaired. If no cracking or crazing is found the repair can be made using Bondo Body Filler, or a similar epoxy body filler. (see: "How to Use Bondo Body Filler")
Larger cracks, tears or missing pieces require a more extensive patchwork. Continue to expose the broken segment using a file or DA grinder to form a "V" shaped groove along the path of the crack about 1/2" wide at the top of the groove. Any broken piece can be replaced with a shaped part to match using styrofoam or other materials, if back side is accessible duct tape in place, if not hold in place with a screw into the part jigged to the good panel. Once repair is done the screw jig can be removed.
Using a Bondo or other fiberglass repair kit which comes with the fiberglass components of resin and hardener, mixing cup, fiberglass blanket and fiberglass mat. Follow all directions on the packaging regarding safe handling and wear protective safety gear, gloves, safety glasses and provide adequate ventilation. Fiberglass material can cause skin reactions in some people and itching so wear long sleeve shirt and full pants. Cut layers of fiberglass, two to three preferred to match the "V" shape and extend past the edge about 1" with top layer.
Once the fiberglass mat, 3/4 to 1.5 ounce weight, parts are cut and placed on a work surface, covered with wax paper, the glass resin can be mixed. Tools required should be at hand and can include: a small paint brush, small laminating roller, Acetone Cleaner and rubber gloves. Mix enough resin with activator (hardener) to soak the parts a few ounces at a time. Pour mix or paint with the brush all layers until completely soaked, allow the fiberglass to "wet" a few minutes especially if the repair area is on a curved or edge wrapped area allowing the fiberglass to follow the contour. While still wet continue to add subsequent layers building up the patch area to level or above the surface. Using the brush to form any contour and to expel majority of entrapped air. Safely dispose of any residual resin mix and clean tools with Acetone, never return mixed material into the resin can. As fiberglass is setting roll the surface smooth using the laminating roller to work out remaining air bubbles and roller action floats resin to surface. Travel in one direction pushing air out. Clean all tools.
Depending on room temperature 70F or above the resin will quickly react and harden. The reaction of the fiberglass resin generates heat when curing. At cooler temperatures or to hasten the cure a heat gun or hair dryer will accelerate the process. Do not cook or overheat keep gun moving, the mixture is highly flammable use extreme caution. When fully hardened the patch can be sanded or filed smooth using progressively finer grit paper starting with 80 grit up to 320 or finer. Any imperfections can be filled using Bondo Body Filler resand and prime and paint with Dupli-Color or equivalent matching paint and clear coat.
