3. Tape It Off
Carefully mask around the edges of the 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 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.
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 paint. If you choose paint, topside alkyd enamels, polyurethanes and others are available from Interlux (yachtpaint.com) and Pettit (pettitpaint.com).