Assess Your Gel Coat Cracks
Almost all fiberglass boats have at least a few cracks in the gelcoat and some boats look like a hardboiled egg shell that has been rolled on the countertop. These cracks tell a story worth following. They might point to some stress that occurred the day the boat came out of the mold. Perhaps the crack resulted from a heavy tool falling on it. Maybe the structure lacks the stiffness needed to resist bending and flex. Learning how to read the cracks will help you decide if they should be repaired and if so, how.
Gelcoat refers to the pigmented resin on the surface of a fiberglass boat. Gelcoat serves two purposes: it seals and protects the underlying laminate from moisture and UV rays, and it helps sell boats at boat shows. Under a microscope, glass fibers look like evergreen trees with branches and needles poking out of the resin ready to wick up moisture. Gelcoat seals the fibers and helps to keep moisture out. Differ- ing formulations seek the optimal balance of color retention, hardness, moistureresistance, flexibility, and ease of repair. Application provides another challenge: too thin, the gelcoat will wear quickly and allow the underlying laminate to show through; too thick and the gelcoat will craze like crazy. The difference between too much and too little can be measured in thousandths of an inch. Given all of these variables and the demanding environment formed by extended exposure to sun, salt, dirt, and movement, we should not be surprised if some cracks develop. It would be a mistake however, to quickly dismiss cracks as minor annoyances.
READING THE TEA LEAVES
Impact Cracks that radiate out from a center, like an asterisk, usually point to impact, such as dropping a winch handle or the crown of an anchor. Impact cracks result from a singular event and although they should be repaired, at least you know that these cracks do not necessarily point to an underlying structural problem.
Stress: These cracks often appear early in the life of a boat and may appear in tight corners, where stresses tend to concentrate. Cracks located at or near hard or tight corners might occur when a part is removed from a mold, or they might develop soon after. Like impact cracks, these
usually point to a one-time condition.
Flex: Cracks caused by flexing usually run parallel to each other. You might find this pattern where the side deck meets the cabin side, with cracks running side by side and roughly parallel. These cracks indicate a weakness in the structure, allowing the deck to hinge with respect to the cabin side. This continual movement eventually breaks down the gelcoat, leading to cracks. Even worse, the movement can fatigue the underlying laminate. Unlike impact and stress cracks, flexing indicates an ongoing situation and will require more than simply repairing the gelcoat.
Crazing: Cracks in random patterns appearing in many areas, suggesting application errors. These can include problems with the product formulation or its application, usually from applying too much material. These cracks tend to appear all
over without apparent rhyme or reason. They might tend to be more abundant in areas that have some stress or flex, but will also appear elsewhere.
On older boats (25 years or more), gelcoat sometimes crazes in short, random
cracks across an entire surface. In these cases the gelcoat has outlived its service life.
REPAIRING GELCOAT CRACKS
Remember that, in addition to the aesthetic benefits, gelcoat serves the impor-
tant functional role of keeping moisture out of the laminate. Cracks create a chink in this armor. Over time, water will wick into the laminate. At a minimum this might lead to elevated moisture readings during a pre-purchase survey. For boats stored in northern climates, the freezethaw cycle might lead to worsening of the cracks. For these reasons, the cracks should be repaired.
Gelcoat cracks cannot be sealed by coating over the top of them. The cracks will expand and contract with temperature changes and the boat’s movement. The coating applied on top of the cracks will soon crack and you will be back where you started. In order to achieve an effective long-lasting repair, the crack must be widened using a Dremel tool or similar. Once the crack has been opened, it can be filled with gelcoat tinted to match. After wet sanding and buffing, the crack will be gone, but matching the gelcoat can be a maddening challenge. Unless you have a new boat, the gelcoat will have aged and changed in color, more so for dark colors like blue, red, and black. Even the correct gelcoat from the builder will not perfectly match aged gelcoat. A skilled craftsman can tweak the color with tint and come very close, but if you are expecting perfection you might be disappointed.
For repairs while cruising or for doit-yourself repairs, a product marketed as Hairline Fix by MagicEzy does a reasonable job. This product has been formulated to provide the viscosity needed to flow into the crack, and the adhesion and flexibility required to remain in place. Color choices are limited and might not be a great match, but in most cases it should be close enough. You will be keeping the water out and the cracks won’t be visible unless you go looking for them.
Either of these solutions will work
for impact or stress cracks, but cracks from flex, which indicate an underlying problem, must be fixed before addressing the gelcoat. These areas will require additional laminations of fiberglass to provide the stiffness needed to reduce the movement that caused the cracks. Identifying the cause and creating a solution requires someone with knowledge and skill working with composites.
For cracks caused by application errors or age, another level of repair will be required. When the deck and cabin surface suffer from hundreds of random cracks, repairing each one becomes unfeasible. At this level of severity the gelcoat must be ground off. The surface can then be sealed with epoxy primer and painted with one of the two-part linear polyurethane paints. Although expensive, this approach will add value to your boat and will retain a high-gloss finish for many years. One more advantage: waxing will no longer be required.
If you have already dealt with gelcoat crazing then you know fiberglass isn’t all it is cracked up to be. Osmotic blisters, wet cores, and failing gelcoat serve as reminders that while composite boats don’t rust and don’t need caulking, they do require a watchful eye. Despite these issues, well-built fiberglass boats can provide decades of safe cruising. Gelcoat cracks have a story to tell, and we should listen. Staying on top of these troublesome cracks can help you avoid more serious and costly repairs later.
TOP: The intersection of the flexible flat deck and stiff vertical surfaces causes cracking. ABOVE: The star or asterisk pattern usually results from impact.
The builder applied too much gelcoat to this boat, resulting in a high number of cracks. Before a crack can be repaired, it must be opened up with a grinding tool.