How to Repair Gelcoat

Own a fiberglass boat long enough, and you’ll end up with a scratch, nick or gouge in the finish. It might be from a muffed landing, a dropped pair of fishing pliers or just a hole drilled in the wrong place. You can usually fix gelcoat repairs yourself. It takes a bit of patience, but do it right and few will notice.

Complications occur when there's damage on a textured surface like diamond nonskid or on a multitone finish. For these, call in a pro. Also, deep gouges may need structural fiberglass work or filler before you repair the gelcoat. On horizontal surfaces, liquid gelcoat works, but for vertical surfaces, a paste is easier to apply. The first step is identifying the finish on your boat.

Getting Started
Finish Time: 1-2 hrs
Skill Level: 3/5

Tools and Supplies
*Masking tape
*Hand-held grinder and bits
*Countersink bit and drill motor
*Gelcoat resin and catalyst
*Coloring agents
*Acetone
*Mixing cups
*Stir sticks
*Latex gloves
*Dust mask
*Cleanup rags
*Putty knife
*Wet/dry sandpaper (320-, 600- and 1,000 grit)
*PVA curing agent
*Rubbing compound
*Boat wax

You'll need to fill deep gouges with resin and filler before applying finish. Epoxy resin and fillers adhere better than polyester products but cost more and require several extra steps prior to applying the finish color of either gelcoat or boat paint. If you choose paint, topside alkyd enamels, polyurethanes and others are available from Interlux and Pettit.

1. Match the Color
For current boats, your dealer might be able to supply matching gelcoat. But due to weathering on your boat, it may not match. There are kits from companies such as Evercoat with pigments to add to the resin for a match. If you have a sample, you can match a gallon of gelcoat from Rayplex Composites (fibreglass.com).

2. Clean Up Edges
Use a rotary grinder to smooth the edges to a 45-degree bevel and eliminate any loose material. If repairing a drilled hole, the surface might have become elevated from the upward pressure of an old fastener. Use a countersink bit or rotary file and a drill motor to carefully grind away the swollen perimeter. Scrape away any old sealant and clean up with acetone.

3. Tape It Off
Carefully mask around the edges of the fiberglass boat repair area with two-inch-wide 3M ScotchBlue Multi-Surface Painter's Tape No. 2090. Give yourself a 16th of an inch of unmasked margin around the scratch, gouge or hole. Also, mask off any adjacent areas or items to protect them from inadvertently applied gelcoat or errant sanding. Clean up the repair area again with acetone.

4. Mix the Gelcoat
After you have color-matched the amount of gelcoat needed for the repair, add catalyst (aka hardener). Different gelcoat resins require different catalysts, so make sure you are using the proper formula, as well as the right two-part ratio (e.g., four drops of catalyst per teaspoon of resin). Mix the two parts thoroughly with a stir stick to ensure that the entire batch will cure at the same time.

5. Apply Gelcoat
Use a small wood or plastic putty knife to spread the gelcoat smoothly over the gelcoat repair. You should have about 10 to 15 minutes of working time after adding the catalyst before it starts to harden and is no longer fluid. Fill the repair slightly higher than the surrounding surface to allow for sanding. If you don't plan to sand, make it even with the surrounding surface. Either way, spray it with a PVA curing agent.

6. Sand It Out
Peel off the PVA. Wet-sand the cured gelcoat with 320-grit wet/dry paper on a soft sanding block. Confining work to the immediate repair area, continue wet-sanding with 600-grit paper until nearly even with surrounding gelcoat. Finish wet-sanding with 1,000-grit paper; then buff out with rubbing compound followed by a coat of wax. If not sanding, just peel off the PVA and apply wax.