How to Repair Fiberglass

Fix gouges: Fill and smooth

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Photo 3: Prepare the filler

Stir in enough chop to get the mixture to the consistency of peanut butter. Then add hardener (follow the manufacturer's ratio) and stir, stir, stir.

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Photo 4: Fill in the gouge

Scoop the gel coat putty into the gouge. Then press it into the fibers with a craft stick. Add more putty until you're about 1/32 in. above the surface. Clean up any goofs with acetone.

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Photo 5: Sand the patch

Knock down the excess putty with 80-grit sandpaper and a rubber sanding block. Then switch to 240-grit.

To fix gouges and deep scratches, you'll need “chop” (powdered fiberglass) filler, gel coat and gel coat reducer. Jot down your boat's model and serial numbers and contact the manufacturer to order gel coat (about $100 per qt.) to match your boat's color. It may not be an exact match, but it'll be a lot closer than mixing colors from scratch. Then order some gel coat reducer (Patch-Aid is one brand; about $49 per qt. from minicraft.com or spectrumcolor.com) to thin the mixture enough to go through the spray gun. For gouge repair, you'll mix chop filler (Chris uses Cab-O-Sil from epoxy5050.com) with the gel coat to create a thick paste. Then pick up paper cups, stir sticks, acetone (for cleanup) and rags. You'll also need a disposable spray gun (Preval is one brand; about $7 online or at paint and art supply stores). To finish the job, you'll need a professional-type buffer. The variable-speed feature is important, and so is the high power of a professional buffer. So don't skimp on one or think you can get by with a $29 wax polisher. Use a wool buffing pad (such as a Dewalt DW4988 pad, available through our affiliation with amazon.com or westmarine.com), and buffing compound (3M Imperial Compound and Finishing Material, which is what Chris uses, available through our affiliation with amazon.com or westmarine.com).

Mixing gel coat is a messy and stinky process—so wear chemical-resistant gloves, safety goggles and a respirator. Start with a small amount of gel coat and stir in the chop and hardener to make a putty that's the consistency of peanut butter (Photo 3). Once you add the hardener, you've only got a 10- to 20-minute “open” time, so mix small batches and work on one gouge at a time. Thorough mixing is critical to proper curing. Spend a full minute stirring. If you don't, you'll end up with patches of sticky resin that can take days to harden.

Overfill gouges so the filler mounds slightly. You'll sand it flush after it cures. Curing can take one to two hours—depending on humidity levels. So test it by touch. If it's sticky, it's not fully cured. Once it's fully hardened, sand it with 80-grit sandpaper (Photo 5).

Fix gouges: Apply the finish

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Photo 6: Mix new gel coat

Add the hardener after you've mixed in the reducer. Follow the manufacturer's recommended ratio of hardener to gel coat.

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Photo 7: Spray on the final coat

Pulse the sprayer to get short bursts of gel coat. Feather the spray along the edges to reduce sanding.

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Photo 7A: Close-up of sprayer

A pre-charged sprayer applies the final coat more smoothly than brushing, but you still have to sand it out.

Now you're ready to mix a fresh batch of gel coat (without the chop) and spray the scratched and patched areas (Photos 6 and 7). Chris recommends using a disposable spray gun and paper cups. Unthinned gel coat won't go through the sprayer. Add the recommended amount of reducer (read label directions) and hardener and mix the ingredients. Spray the patched areas with short bursts. Spraying gel coat isn't like spraying paint. It splatters on and has to be sanded and buffed to get to a smooth gloss. So don't be disappointed that the finish isn't paint-like right away.

Final-sand, buff and wax

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Photo 8: Buff to a great shine

Take a seat and heft the buffer into position. Start slowly and buff small sections at a time.

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Photo 8A: Close-up of buffing compound

Buffing compound produces a silky smooth finish.

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Photo 9: Apply new decals

Position the new boat numbers and tape the sheet in place. Then lift the sheet up, remove the backer and press each number individually. Don't try to apply them all at once—they'll wrinkle.

Wait for the gel coat to cure. Sand the repairs with 600-grit and then 800-grit sandpaper. For the perfect finish, sand with 1,200-grit wet/ dry paper then buff (Photo 8). Apply buffing compound directly to the pad. Work on a 2 x 2-ft. area and use light to medium pressure at a fairly low speed. Reduce pressure as the compound starts to dry. Wipe off the haze as you go. Apply the graphics and then wax.