| Gelcoat Repair: Mixing and Applying the Gelcoat |
From "Shipshape Boating"
episode DSSB-108 |
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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 Mixing the Gelcoat Before mixing the gelcoat, you may want to consider some options: - A gelcoat tint kit (figure A) that comes with a base-white product and various tubes of tint. This is a more difficult way to match the color of your original gelcoat because you have to test the various tints in with the white base until you come up with the proper color. Many times you may not get an exact match to the original gelcoat.
- You can use the manufactured tubes of gelcoat that are sold for most crafts as an "after" product, but remember, over time the entire surface color of your boat may change slightly, and the original product will be the perfect original color.
- You can get a company to match the original gelcoat by sending a sample such as a hatch to a storage area. Many companies will take sample and scan it in to a computer (figure B), where the computer will match the color. This method will give you an exact color match. This is the option that host John Greviskis went with for this particular on-air project.
Before you mix up the new gelcoat, you'll need to add a few items to the mixture: - Add MEKP (Methyl, Ethel, Ketone and Peroxide), which is a type of hardener used for polyester-based material. You simply add about 1 ounce of the MEKP, which is a ratio of 10 percent MEKP to gelcoat.
- You also need some kind of agent inside the gelcoat in order to cut off the outside air supply. This agent is called a surfacing wax. Use five percent by volume here. (Gelcoat will never harden, no matter how much hardener you use if left exposed to the outside air.)
- The final touch is to add a thickening agent -- colloidal silica, also known as "Cavasil" -- to the gelcoat to get the right thickness (like thin paste or creamy peanut butter -- figure C).
- Stir gelcoat mixture until it is smooth.
- Outline each repair area with masking tape so you only get the gelcoat to the areas needed and no drippings.
- Add enough material to the repair area so that the height of the new gelcoat is slightly higher than the height of the surrounding gelcoat (figure D). This way when it cures you can come back and sand the gelcoat down.
Note: It's best to let the gelcoat cure for at least 24 hours. You want to make sure it's dry and solidly formed. - Using a rubber sanding block and 320-grit wet/dry sandpaper, wet sand the gelcoat down trying to stay as close to the new gelcoat (figure E). Sand the area going in several different directions. Make sure that your keep the paper wet by occasionally dipping it into a bucket of water. You want to do all the damaged spots like this.
- Now, switch out to 500-grit wet/dry sandpaper and wet sand just a little farther out away from the center of the repair than where you sanded before. This is how you blend this area to the rest of the boat. At this point you don't want to use block sandpaper. It's easier to bevel out the edge if you use the regular sandpaper by hand.
- Now it's time to progress to a 800-grit wet/dry sandpaper. Again taper out the sanding just a little bit further. Each time you go up in grit paper your actually sanding out the scratches that we just cut into the gelcoat with the previous grit paper.
- The final sandpaper you'll use is 1,200-grit wet/dry. Copy the previous two steps.
- The final sanding doesn't involve sandpaper at all. You'll use a variable-speed buffer and some medium course rubbing compound. You'll need compound that equates to about 2,000-grit (coarse) wet/dry sandpaper.
- First, put a dab of the compound on a dry lambs wool buffing wheel (figure F). Smear it onto the area of the boat, applying it in circular motions. Set the speed on the buffer to 1,500 RPM and go to work. Tilt the wheel so that the top third of the pad is coming in contact with the boat hull. Rotate any slower and the rubbing compound will not adequately cut into the gelcoat, and if you rotate any faster and you might wind up burning through he gelcoat.
- Make sure to overlap your strokes.
Safety Alert: Be sure to wear safety goggles and a dust mask when buffing the gelcoat. You may want to consider wearing a protective suit as well. Tip: If the buffing wheel becomes clogged with dried gelcoat compound, a great way to clean it is to turn the machine on, insert a spurring tool (figure G). Insert the tool at a 45-degree angle and turn the buffer on. This removes the entire dried-up compound. Waxing the Boat - The only thing left to do is wax, which is used to seal the gelcoat and protect it from oxidizing. It protects the longevity of the gelcoat and is what keeps it from getting chalky.
- Using a quality marine-grade wax, first apply it to the hull sides using a wheel. Use tiny overlapping strokes. Once you get a side done let it haze over so that it is completely dry and then use a clean terry cloth towel to remove all the haze.
Note: - For southern climates, wax the hull every six months and the deck every three months.
- For northern climates, wax the hull every 12 months and the deck every six months.
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