How to Gel Coat a Large Area

Gel coat is typically used to cover fiberglass boat hulls.

Gel coat is a resin coating that is typically used to coat fiberglass. Though this finish protects the fiberglass, it is possible to damage a gel coat finish, especially if it is protecting an item that is exposed to the outdoors. Gel coat kits are typically designed to repair a small area of damaged gel coat, but you may need to repair a large area, or you may want to add a new gel coat finish to an item. If you are working with a large area, a sprayer is the best way to apply gel coat.

Things You'll Need

• Sandpaper
• Cloth
• Acetone
• Respirator
• Suction-feed paint spray gun
• Gel coat
• Mold release

Instructions

1. Clean and sand the area to be gel coated. Remove any residue or paint, and sand the area using 220, 320, 800 and 1000-grit sandpaper, moving from coarse to fine to get a smooth, even surface.

2. Rub the entire surface with acetone and a cloth, then wait for it to dry. This removes any grease, oil or wax from the item. These substances interfere with proper gel coat adhesion.

3. Prepare your workspace. Protect your work area, put together the spray gun and put on a respirator. Once you mix the gel coat, it will immediately begin to set, so you must be ready to start working as soon as it is mixed together.

4. Mix your gel coat in the paint cup according to the instructions, stirring for about a minute. Add tint to the gel coat before the hardener if you are using colored gel coat. Do not mix more than you can easily spray in within ten minutes.

5. Thin the gel coat with acetone. This will make spraying easier and prevent unwanted texture in the finish. Do not add more than 10 percent acetone to the gel coat.

6. Spray the item using thin, even coats. Do not move too quickly, but do not move so slowly that you develop an overly thick coat.

7. Wait for the coating to cure and add another coat if needed. You may need two or three coats. Clean the spray gun between coats using acetone. If the gel coat sets inside the gun, it may ruin the gun.

8. Spray the area with mold release when you have sprayed your final layer of gel coat. Many gel coats do not cure correctly in air, and mold release will seal the gel coat so that it can finish curing. Wait for at least 24 hours, then wash off the mold release with soap and water.

9. Sand the coating gently with sandpaper.

Tips & Warnings

• You may want to use a primer. This will help prevent pinholes from forming in a large area of gel coat.

• You must clean the spray gun immediately after use using acetone. If the gel coat begins to set up inside the gun, immerse it in acetone. To make your work easier, you can use a spray gun with disposable parts so that you have fewer items to clean.

• An automotive spray gun has the appropriate tip for gel coat application.

• Do not work on very hot days or in direct sunlight, as the gel coat will cure too quickly. Do not work at temperatures below 60 degrees Fahrenheit, as the gel coat will not cure.

• Acetone and gel coat both have hazardous fumes. Wear your respirator at all times.

References

• Boat Repair Videos: Tips With Fiberglass and Gelcoat Repair Methods
• Spraygun Industry: Gel Coat
• American Marine Supply: ITW Evercoat
• Fiberglass Hawaii: Gel Coat Usage