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Repairing scratches on a fiberglass boat is a relatively simple process, albeit a bit on the messy side. You will basically be refilling the gouged out area with new fiberglass. Shallow scratches are easily fixed. With deep scratches, you’ll have a more complicated task ahead of you. But both projects can be done by the weekend mechanic.
Items you will need
Dish washing soap
Epoxy fiberglass resin and hardener
4-6 oz. E-glass fiberglass fabric (4 by 8 inch square)
Disposable mixing cup and stirring stick
Sharp knife or chisel
Sandpaper and sander
Styrene (small bottle)
Plastic flexible spreading tool
Latex or rubber gloves
Power buffer and fine grade buffing compound
Clean the hull around the scratch with soap and water, then wipe with a rag saturated with acetone. Wear gloves while handling acetone and all fiberglass liquids.
Drag the point of a knife or corner of a chisel down the scratch to widen it slightly to accommodate the repair material more readily. Lightly hand-sand to remove any bits of fiberglass sticking up along the edges of the scratch. When the scratch edges are level with the rest of the hull, you’re ready to go.
Mix up a small amount of epoxy-based fiberglass resin. For most scratches you’ll use less than a quarter cup of resin.
Pick fibers loose from the edges of a piece of lightweight fiberglass fabric with your gloved fingers or a small sharp knife blade. When you have a little pile of them, place the fibers next to the scratch. Dip the fibers into the resin cup and lay them in the scratch. Stagger the threads so their ends overlap. As the fibers fill up the crack, brush lightly over the top with the fiberglass resin. Use the spreader tool to press the resin flat across the top of the crack and smooth out any air bubbles or bumps.
Allow the resin to set and cure overnight. Lightly sand with fine sandpaper and then fine steel wool. Polish and buff with buffing compound to a shine that matches the rest of the boat. For very light scratches, polishing and buffing over the scratch may be all you need to do, and you can skip the fiberglass mess.
Use a sharp knife or corner of a chisel or screwdriver to clean out and widen the scratch so the repair material will set better. Clean the area around the scratch and wipe with an acetone-dampened rag.
Sand the edges of the crack to remove any burrs sticking up above the hull's surface.
Mix up a small batch of gelcoat paste. Gelcoat paste repair kits come with a selection of pigments to mix with the paste to match the original color of the boat. This is the hardest part. If you can find a matching color swatch at your local paint store, they can tell you what pigments in which proportions will match your color. Get the color as close as you can. Buffing may help disguise any minor color variation. Color the paste before you add the catalyst. Add the pigments one drop at a time to an ounce of paste in the proper proportions. When the paste is a close match, put a drop on the boat hull to see how close it is. When it’s right, write down the number of drops of each pigment per ounce for mixing later batches of gelcoat paste. Add the catalyst and stir. Refer to the directions for hardening times.
Wipe the scratch with styrene before applying the gelcoat paste. This reactivates the old gelcoat and helps improve the bond between the old fiberglass and the repair.
Spread the paste into the scratch with your spreader. The paste will bulge up a little after the spreader goes over it. Don’t let it bulge too much or you’ll have a lot of sanding to do. Wipe off any excess paste. Cover the gelcoat with a sheet of plastic film and tape it down. Gelcoat won’t fully cure in the air. Let the repair cure for 24 hours. Sand with fine sandpaper, then with very fine wet sandpaper and finally with fine steel wool. Buff with rubbing compound to a high gloss then give the hull a coat of wax.
- Wear a respirator or work outdoors or in a highly ventilated area.
- Wear gloves whenever handling fiberglass resins and solvents.
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