In this week's episode of DIY's Shipshape Boating, host John Greviskis demonstrates how to repair and maintain the finish -- or gelcoat -- on a fiberglass boat. What is Gelcoat? Boat builders start with a fiberglass mold (figure A) that is supported by metal on the outside (to make it structurally sound) and on the inside, a gelcoat over top of the fiberglass to make it smooth. To get the mold to pop out, a release wax is used. After waxing the mold thoroughly, a polyester-based material called "gelcoat" is sprayed on every square inch of the mold. A chopper gun is then used to shoot out chopped-strand mat (fiberglass) along with polyester resin (figure B) all over the mold. The mat and resin is rolled along the entire surface of the mold, and then the structural fiberglass cloths are added. Once all of this cures, the gelcoated deck separates from the deck mold. The gelcoat has been designed to cure without the presence of air. Starting the Gelcoat Repair Materials: Die grinder and bits
Dust mask and glasses
1,000-grit wet dry sandpaper
1,200-grit wet dry sandpaper
1,500-grit wet dry sandpaper
Blue masking tape
Safety glasses
Dust mask
Gloves
Acetone
Rags
Gelcoat or tint kit
Mixing sticks
Plastic cups
MEKP
Marine wax
Surfacing wax
Yellow spreaders
Sanding blocks
Painter's tape
Cavisil
Buffing compound
Buffer
Buff pads
Wax pads
Terry cloth
Spoke - The first thing you need to do before repairing gelcoat is to tape off the rub rail with blue masking tape (figure C).
- Put on a pair of safety glasses, a dust mask and start the process of grinding out all the fractured areas of the gelcoat.
- Once you've found all the cracks and damage to the gelcoat, use a high-speed tool with a cone-shaped grinding bit on it to remove even more gelcoat (figure D) from the boat so that you get down into some un-fractured fiberglass. This will give you a solid foundation to be working on. (The loose material must be ground out).
- Feather the edge of the repair area in order to give the new gelcoat a much larger surface area to bond to.
Tip: If you don't have a high-speed grinding tool available, you can do the repair with some ordinary materials you'll find in your kitchen or garage. For example, a hand-held can opener can scratch out any of the fractured gelcoat. Just be sure to come back with some 80-grit sandpaper to bevel out the edges. - Clean the area by removing all the dust and loose fiberglass from the grinding by using acetone and a rag (don't ever let acetone touch your skin). Be sure to use a different section of cloth for each wipe in order to keep it dust free.
Warning: If you don't remove the debris thoroughly, when the new gelcoat is applied, it may not bond properly. In the next segment, Greviskis explains the process of mixing the gelcoat and applying it to the craft.
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