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 Exterior Surface PreparationTo get a quality gel-coat repair, you need to prep the damaged area properly. This means chipping away any loose material and clearing the gel coat away so that you’ll be applying new gel directly to a stable fiberglass substrate. I use a motor tool with an abrasive bit to do this work. You may follow individual cracks with a fine bit or rough out the area between closely spaced cracks. Be careful not to remove the fiberglass laminate itself as you grind down through the gel coat. You’ll want to taper or “feather” the edge of the repair area into a shallow dish or “V” shape as you work. The next step is to sand with 150- to 220-grit paper. Using the sandpaper, continue to feather the edges of the prepped area. Work out onto the hull of the boat so that you’ve sanded a spot that’s roughly rectangular and extends at least an inch beyond the bare fiberglass. If you have a Kevlar kayak, you’ll have trouble with prep because of the material’s tendency to “fuzz” when it’s sanded. On a Kevlar boat, it’s best to do all of your prep with a razor knife and to keep your sandpaper as far away from the substrate as possible. If you have some fuzzing, you can still complete the repair. Loose strands that are captured in hardened gel coat are more sandable. Just be prepared for a less-than-perfect result. Once you’ve finished sanding, wipe the surface of the repair with denatured alcohol, making sure to remove all surface debris. Next, mask off the area around the repair with blue 3M masking tape. This tape is preferred, as it doesn’t leave a sticky residue when it’s removed. Make sure that your masking tape overlaps the edge of the sanded area, so that when you apply gel coat, it will only be applied to a sanded surface. If the repair is to be done on a surface that isn’t flat, you may need to create masking-tape “dams” to prevent drips. Creative use of masking tape will also help you build up thicker layers of gel coat to repair deep chips or gouges.  Applying the Gel CoatMost kayak hulls are white, and white gel coat is available at most marine supply stores. If you’re trying to repair a colored hull or deck, you’re often best off contacting the manufacturer of your kayak for pigment or gel coat. Some manufacturers will send you a small vial of pigment for free, which may then be mixed with clear gel coat to create the proper color. Other manufacturers sell small containers of colored gel. It’s safe to assume that, because of sun fading or darkening, your color will not match even if you get it directly from the manufacturer. Most repairs blend with time as the patch weathers. First, the gel must be mixed with catalyst in the proper ratio. This ratio is specified by the manufacturer, but in practice, polyester gel coats are fairly tolerant of imprecise mixing. I typically use small waxed-paper cups for mixing. With one-quarter inch of gel coat in the bottom of one of these cups, I add about 15-20 drops of catalyst. This ratio is a bit “hotter” than recommended, but it works well. Once you’ve mixed your gel coat, you have only a certain amount of time that you can work with it. As with the resin, gel coat’s cure time will vary with the temperature of your workspace and the amount of catalyst. This also applies to the thickness of the gel coat that you apply to the hull. A super-thin layer of gel will not cure at all unless you add extra catalyst. Most of the time, ratios of catalyst for home use are measured in drops per ounce of resin. In cool temperatures, or with tiny batches, you need to add more drops. In these circumstances, I might add 25 drops to my cup of gel coat. The ratio of catalyst to resin should never exceed two percent. This is pretty difficult to measure in small batches, and in practice, finding the correct ratio often relies on experience and a bit of guesswork.  If you make a mistake in your catalyzing ratio, the results are predictable and
repairable. Too much catalyst will cause the gel coat to overheat and will fill
your patch with tiny bubbles—a cosmetic flaw. Too little, and your patch
will not harden. Repairing such mistakes is straightforward, if a little frustrating.
If you under catalyze, wipe the gel coat off of the hull with acetone and start
over. If you over catalyze, sand the patch again and apply more material. If
you are concerned about your ratio, try a small test batch on a piece of wax
paper before you apply the gel coat to the hull.Gel coats are designed to cure in an air-free environment. When a kayak is built, the gel-coat layer is put into the mold first and allowed to set a bit before the fiberglass is laid over it. When you do repairs, you are essentially working backward and need to create a barrier to oxygen so that the gel will harden properly. The barrier can be created by taping a piece of waxed paper over the wet gel once you’ve applied it. However, this tends to put ripples into the surface of the patch. I prefer to add waxed styrene as a surfacing agent.  Waxed styrene is hard to find in the U.S. I make my own by shaving tiny flakes
of canning paraffin wax (available at grocery stores) into straight styrene (supplied
by many marine stores). Shave paraffin into the styrene and stir the mixture
until the wax dissolves. If you add too much wax, the mixture will become cloudy.
Add a bit more styrene if this happens. If you use waxed styrene, add about 10
percent to the gel-coat mix before you add the catalyst. If you can’t find
styrene, you may use waxed polyester resin instead. Mix 25 percent resin with
75 percent gel coat. This technique works well but tends to darken the gel coat
a bit. Consider adding pigment to the gel coat if you’re using waxed resin
instead of styrene.There are many ways to apply the gel coat to your kayak. I have seen people paint it on, scrape it on with a razor blade, dab it on from the end of a stirring stick or pour it into a masking-tape dam—all of these work. Brushes work well but may leave bristles in your work. Foam brushes are good for thin layers but may dissolve and disintegrate during application. Hobby brushes with fine bristles work particularly well for applying gel coat precisely to small areas. Apply a first coat thick enough to fill the gouges and restore the contour of the hull once you’ve sanded. Keep in mind that the gel coat will shrink as it cures. Apply gel coat to the hull so that it covers the prepped area up to the masking tape completely. Once the gel coat has started to harden a little, peel away the masking tape to reveal a clean edge. If you wait too long, the gel coat will harden completely, and you’ll have to chip it away from the tape before you can sand. |
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