Caulking Holes in Fiberglass

Determining Damage

• Plugging a hole in fiberglass won't help strengthen the entire panel if damage radiates out from the puncture. According to boating repair expert Don Casey, tapping the edges of a fiberglass impact hole with the plastic handle of a screwdriver can reveal the extent of damage. Solid fiberglass sounds sharp and bright when you tap on it, whereas damaged fiberglass sounds dull or flat. Identifying the true extent of the damage can help you determine how much of the fiberglass panel to remove before attempting any repair. Failing to do so could only worsen the problem instead of fixing the hole.

Thickened Epoxy

• Thickened epoxy works best for repairing fiberglass panels that routinely get wet, including shower doors. According to West System, a fiberglass repair company, it's necessary for you to create a clean, sanded and porous fiberglass hole before using epoxy to repair the opening. Adding a high-density filler or colloidal filler to the epoxy is also necessary to thicken the compound and help it match the look of the surrounding fiberglass. These thickeners make epoxy harder to sand. Avoid overfilling the puncture area to keep sanding efforts to a minimum once the epoxy dries.

Polyester/Vinyl Resin

• Polyester or vinyl resin is ideal for repairing holes in fiberglass that doesn't get wet on a regular basis. According to Don Casey, a catalyst, including methyl ethyl ketone peroxide, is necessary to harden vinyl or polyester resin. Four drops of hardener is necessary for every ounce of resin used in repairing a fiberglass hole. Stirring resin thoroughly helps the hardening agent mix properly through all of the resin. Adding too much hardener can cause the resin to weaken and reduce laminating strength.

High-Risk Repairs

• High-risk repairs in fiberglass require more than epoxy or resin. According to West System, such repairs are needed in fiberglass panels that have extensive damage, including severed sections or deep cracks. Repairing these holes requires adding fiberglass backing panels to support the structures and provide areas for resin or epoxy to fill gaps. Adding epoxy or resin in layers is necessary to preserve the integrity of the fiberglass panels. Adding fillers all at once can increase drying times and may compromise the panels before they can properly bond.