Crack on gelcoat

A frontal impact is indicated by a circular pattern, with the diameter of the inner circle related to the size of the impacting object. In other words, the larger the object, the larger the radius of the crack. There are two types of linear cracks: stress field patterns and parallel stress cracks.

The primary cause of these cracks is flexed strain on the gelcoat. Parallel stress cracks indicate movement opposite the direction of the cracks. Parallel cracks indicate a distribution of stress over a supported panel surface. The more flexible the panel or surface, the more likely the gelcoat will crack. Thermal fatigue cracks result from constant expansion and contraction of the gelcoat film.

Cracks are identified by short discontinuous sections and are usually grouped in sections. Each section is roughly the same size and shape, indicating cracks resulting from the same movement pattern. The contraction and expansion move in the same way across a portion of the surface. As a rule, it is almost impossible to prevent gelcoat cracks. However, there are some things you can do to either prevent early cracking or the expansion of a single crack.

For instance, you can countersink holes through the gelcoat. This method redistributes the stress onto the structural fiberglass and not the fragile gelcoat.

When holes are drilled correctly, you can preserve the gelcoat longer without cracking or chipping. You'll need to grind down through the crack until you've exposed uncracked gelcoat or fiberglass beneath the surface, but don't try to rush this part of the job; let the bit and its speed do the work, as opposed to applying a lot of pressure.

It's usually best to run the Dremel along each crack lightly then go back and do it again, as opposed to trying to grind deeply on the first pass. Once all the cracks have been ground away with the Dremel, re-sand the area with the sandpaper to smooth out any rough edges or burrs.

Wipe away all of the sanding dust and ground fiberglass bits, then wipe down the entire area with the rag dipped in solvent again. It's very important at this stage to ensure that the surface is completely clean and uncontaminated.

Using gelcoat paste, add a coloring agent to match the color of your gelcoat, if necessary. Most gelcoat pastes are available in white or neutral colors, but straight out of the can they rarely match aged gelcoat. Remember, gelcoat can change color slightly as it hardens, so to match it exactly you'll need to mix a test batch or two, allow it to harden on a piece of cardboard, and then compare the final color against your existing gelcoat. Also remember that the new gelcoat will fade at a different rate than the rest of the boat, and a few years down the line, the difference may become visible.

When you're satisfied with the color match, mix a final batch and use it to fill the cracks and cover all sanded areas. Make sure no air bubbles or gaps are left in the cracks, and use a plastic resin spreader, putty knife, tongue depressor, or similar object to smooth out the surface. When you're satisfied you have a good, smooth surface, cover it with a piece of plastic wrap to allow it to cure completely.

Some gelcoat repair kits will include plastic film for this purpose because gelcoat paste must be sealed off from the air to cure percent. Caution: Always ensure adequate ventilation when working with fiberglass gelcoat — the fumes may be harmful! After the gelcoat has cured, wet-sand it with fine to grit sandpaper until the surface is almost completely flush and smooth; then gently wet-sand it with a super-fine grit sandpaper, and finally, with ultra-fine or grit sandpaper.

Then stand back and admire your work. Good job! This will prevent the threads from creating pressure on the gelcoat and make a small pocket for sealant to help seal the screw. If the gelcoat cracks were caused by fiberglass flexing, add some fiberglass reinforcement to the backside to help prevent future cracks.

If a screw hole repair has a fiberglass core behind it, seal the core with epoxy. Both methods provide a good seal on the core and more holding strength for the fasteners. These gelcoat cracks are stress cracks at the corner of a companionway. A concentrated group of cracks generally running in the same direction indicates a more severe problem. This is often found on the leading edge of the cabin top where it meets the deck.

This can be the result of a high flex area enduring heavy seas or too much load on the boat. Cracks may also form at a bulkhead or other hard spots behind the fiberglass when the boat flexes, creating pressure. To repair this type of cracking, remove the gelcoat from the area and inspect the fiberglass for deeper cracks. Simply wipe the area with a wet cloth so the cracks or fractured fiberglass will appear as white lines in the laminate.

Continue until the fractured laminate is removed, then do a traditional fiberglass repair following these steps:. Cut fiberglass patches starting with the largest first, working your way smaller to fill the area that has been ground away. Repeated treatments gave more improvement. It took just a few minutes of easy work, and after six months was still good.

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