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Gel-coat scratches in a fiberglass kayak are a fact of life. If you paddle often and paddle hard, you’re bound to scuff up the bottom a bit. This is good. It means that you’re spending time out on the water enjoying your boat. If you can learn to ignore superficial scratches in the gel coat, your life will be better. However, there comes a time when even the most hardened boat abuser starts to think about fixing things up a bit. Extensive spiderweb cracks, chunks of missing gel or wear through to the glass laminate are worth taking a look at. The good news is that working with gel coat is not terribly difficult. Even mere mortals can get a polished gel-coat repair. The basic procedure for making a repair has five parts: internal hull patching, surface prep, gel-coat application, sanding and finishing. If you follow this progression and are patient, you’ll get good results.  Causes of DamageBefore you begin your repair, it makes sense to think about what causes gel-coat damage in the first place. There are three primary sources: impacts, abrasions and repeated stress. Impacts may damage gel coat by deforming the hull enough that the gel exceeds its ability to flex. The resulting fracture in the gel coat will often look like a star or a spiderweb. With a heavy impact, it’s possible to break a chunk of gel coat off of the hull, leaving a deep gouge or even a hole in the boat. Abrasion often happens to the keel of a kayak at the stem and stern. Fiberglass and gel coat are quite abrasion resistant; however, dragging over rocks or coarse sand can wear through the gel. Heavy abrasion to the keel is often repaired by the application of a full keel strip to the kayak. Minor abrasions may be fixed, as outlined in this article. Cracks from repeated stress are also common. This is particularly true in boats that have rigid bulkheads rather than foam. The bulkhead in this case creates a hinge point or “stress riser” against which the hull flexes. Repeated flexing over time may soften the laminate in this area and give rise to cracks that run across the hull at the bulkhead. It’s not safe to assume that the fiberglass beneath the cracks is undamaged. If the boat was impacted hard enough to crack the gel coat, or if it’s been flexing at the bulkheads, the underlying laminate may be weakened. Even if there’s no visible damage or leakage, the fiberglass may have been stressed enough to lose some of its integrity and strength. If this is the case, you’ll need to apply a patch to the inside of the hull to prevent the cracks from returning.  Materials CompatibilityThe vast majority of fiberglass kayaks are made with polyester resins. Some Kevlar kayaks are laminated with vinylester or epoxy resins. The techniques outlined in this article are intended to be used on kayaks that are laminated with polyester or vinylester resin and polyester gel coat. If you have a kayak that’s laminated with epoxy, you won’t be able to use the materials listed here (polyester resin and gel coat will not adhere to epoxy). The greatest likelihood is that your kayak is laminated with polyester resin. If you’re in doubt, contact the manufacturer. Health Precautions Whenever you’re working with fiberglass, make sure that you take precautions against dust, fumes and chemicals. Wear a dust mask while sanding and a respirator that protects you against chemical vapors. Nitrile gloves offer good protection against the chemicals that you’ll be using, most of which can be absorbed through the skin. Work in a well-ventilated area. I  nterior Fiberglass PatchingYou only have to apply a fiberglass patch if the hull is soft in the area of the gel-coat damage. If not, skip this step and proceed directly to surface preparation. For patching, you’ll need fiberglass mat, waxed polyester resin, hardener and sandpaper. Glass mat is an unwoven fiberglass cloth that looks like blotter paper or felt. It’s commonly available in an ounce-and-a-half weight and works well for patches because it conforms to curves and absorbs enough resin to be stiff. Fiberglass cloth has a higher tensile strength than glass mat and is used in the construction of light, strong kayaks. However, glass cloth doesn’t hold as much resin and is harder to conform to tight spots. Waxed resin contains paraffin wax as a surfacing agent. Unwaxed resin will dry with a sticky surface and is used for laminating multiple layers of glass cloth. Waxed resin will dry with a hard, waxy finish. If you need to put another layer of cloth or resin onto this surface after it has cured, you must sand the wax off and wipe with a solvent-like acetone or denatured alcohol. You’ll need a workspace temperature above 65˚F. Polyester resin is sensitive to temperature, and both the kayak and the workspace must be warm for your repairs to cure. The ratios for catalyzing resin are usually calculated at 77˚F. Temperatures cooler than this will slow the hardening of your repair. Temperatures warmer than 77˚ will speed hardening and shorten the working time or “pot life” for the resin. A large batch will cure more quickly than a small one. With 80- or 100-grit paper, sand the area inside the hull that is to receive the patch. When you’ve thoroughly roughed the surface, wipe down the sanded area with denatured alcohol. Next, cut a patch of glass cloth about a half inch larger than the damaged area. Catalyze the resin to the ratio recommended by the manufacturer. This ratio is typically 15 drops of hardener to one ounce of resin. Place the patch onto a piece of scrap cardboard or wax paper and apply catalyzed resin with a brush (an inexpensive chip brush works well) until the fiberglass cloth becomes translucent. Paint a thin layer of resin onto the hull where you’ve sanded. Remove the “wetted out” patch from the cardboard and apply it over this resin. Using the same brush, paint more resin onto the patch until the surface is smooth and there are no visible air bubbles. Allow the patch to cure and sand it to ensure that there are no sharp edges inside the hull. Wipe with alcohol as before, and catalyze a bit more resin. Paint a thin coat of resin over the patch to complete the repair. For a simple gel-coat crack where there’s no major structural damage, you usually don’t need more than one piece of ounce-and-a-half fiberglass mat as a patch. However, some people may choose to lay a piece of woven fiberglass cloth over the mat patch to more closely match the appearance of the inside of the hull. If you choose to do this, cut the woven cloth about a half-inch larger than the mat patch, and wet it out at the same time. Lay the wetted-out cloth over the mat. Finally, finish the repair with additional resin and sanding as outlined previously. It’s possible to pigment the resin in an effort to match the hull color. Left to its own devices, polyester will cure a translucent brown. |
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