How to Fix Gelcoat Gouges

I wrote recently about how to about fix light scratches in gelcoat, and also outlined how to find gelcoat suppliers. But what if you’re looking at a used boat with deeper scratches? What’s involved in fixing them? Well, first, the process involves bargaining for a lower price than is advertised. Once you get it home, here’s what’s involved in bringing it back.

Preval sprayers let you spray gelcoat without the need buy a compressor and professional paint equipment.
Preval sprayers let you spray gelcoat without the need buy a compressor and professional paint equipment.

If your scratches are big enough to require spraying on gelcoat, but you don’t have a compressor with a water separator and a paint gun, you can still make the repairs in your driveway. Most automotive paint stores sell the Preval sprayer, a paint gun that uses a disposable can of propellant and a reusable glass jar for the gelcoat. It allows novices to use professional materials and get good results—and it’s a snap to use.

If you haven’t spray-painted anything, Preval has a YouTube channel with gobs of instructional videos.

You will have to add the proper ratio of peroxide hardener when using gelcoat, and there are dire consequences if you add too much: It catches fire. Chlorinated products, such as bleach or pool chemicals that come in contact with gelcoat have the same effect.

The rule of thumb is 4 cc of hardner for 1 pint of gelcoat, or 30 cc per gallon. However, mix only what you plan to use and read the label before mixing. If you add hardener to the whole quart, the gelcoat will “kick off” right in the can and harden.

It’s also important to use the right thinner if your repairs call for spraying on gelcoat. Never thin it with acetone. Gelcoat is simply resin with pigment added for color, so if you thin it with acetone you will get a color change. Thin it with styrene. The gelcoat supplier can help you get the right chemicals.

Scratches that extend down into the fiberglass involve more work, but it  isn’t impossible for the novice. Begin by sanding around the area and the scratch with 320-grit paper. Again, be cautious not to remove too much material. After sanding, use a Dremel tool to clean out the gouge a bit, then feather the edges of the scratch with 180-grit. This helps the gelcoat blend in and helps hide the edges of the filled scratch.

If the scratch is on a vertical surface, you’ll find it easier if you “cup” the gelcoat against the hullside with ordinary masking tape. Unnecessary on horizontal surfaces, the tape keeps the gelcoat from dribbling down the hull until it has had ample time to cure. Use a fine paint brush, the torn end of a paper match, or even a zip tie to dab on the gelcoat.

Once the gelcoat is cured, remove the tape and begin sanding away excess with 320-grit—again, using the X pattern—until the new gelcoat is nearly flush with the hullside. Then switch to 400 and 600 grits and proceed as you would in the steps outlined here.

Bear in mind that all the materials you’ll be working with are hazardous. You should use latex gloves and respirators the whole time. The repairs are messy and time-consuming, but it is possible to achieve decent results in your driveway. Or you could just write someone a check.


  • Preval Sprayers, 300 E. North Street,
Coal City, IL 60416, 877-753-0021,
  • 3M, 
3M Center,
 St. Paul, MN 55144-1000, 888-3M-HELPS,
  • Spectrum Color, 1410 37th Street Northwest,
 Suite F, 
Auburn, WA 98001, 800-253-1366,
  • Mini-Craft, 900 Industrial Drive, 
Wildwood, FL  34785, 800-282-8244,



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