How To Repair Hairline Cracks In Gelcoat

By Terry Monville – GBI Technical Advisor

Knowing how or why your boat's gelcoat cracks occurred in the starting time identify is the key to a successful repair. For example, if hitting a seawall or dropping a champagne bottle on deck is what caused the cracks, later fixing them you will know how to prevent them in the future: Don't potable the champagne causing yous to hit the seawall and drib the bottle.

Then there are those cracks that seem to announced in the gelcoat from nowhere: in cabin and cockpit corners, around screw holes, or in the middle of the deck. It can be difficult to figure out what caused them.

And so, What is Gelcoat?

Gelcoat is a pigmented, high-quality polyester resin used as the cease on fiberglass boats. Like any other polyester resin, it has good points and bad. Let'south await at some of the bad points that lead to bang-up.

Later it's applied, gelcoat shrinks iv to 7 percentage during the cure and can have less than 1 percent elongation. This contributes to gelcoat's prissy difficult finish which we like, only also makes gelcoat brittle, specially if it was applied thicker than recommended.

Gelcoat should be about 20 mils (.020 of an inch) thick when the manufacturer properly applies it to the mold. But when the builder sprays gelcoat on the mold of a boat deck with cabin pinnacle corners and seat backs, the edges tend to get more than needed. Or the gelcoat runs down and builds up in an inside corner, or too much or as well little gelcoat gets sprayed on the whole mold.

Minor Unmarried Line Gelcoat Cracks

A modest single-line gelcoat crack.

Thick areas of gelcoat don't have reinforcing fabric to help concord it together. The stress is relieved in the form of a crack. This can happen when the part is pulled from the mold or years downwardly the road, where a petty more stress is introduced from the part flexing. Generally, these cracks will appear every bit single-line gelcoat cracks in the cabin or cockpit. This blazon of cracking is hard to avoid and is role of boat ownership. Luckily, the repair is unproblematic and straightforward, as I'll explain afterward.

Another common cleft is a screw pigsty crevice: a hairline cleft or two coming from a slice of deck hardware. This can happen later a self-borer or canvas metal spiral is used to add a piece of hardware, even if you lot've used a proper airplane pilot hole for the screw. The threads on the spiral create pressure on the gelcoat causing information technology to crevice. Non using a pilot pigsty, or using one that is also small, will create fifty-fifty more of an upshot. They are oftentimes seen effectually snaps for canvas and beverage holders. When mounting hardware with self-tapping screws, you should drill the pilot hole and then countersink to remove the gel-coat to the threads' diameter. This volition prevent the threads from creating pressure on the gelcoat and make a pocket-size pocket for sealant to help seal the screw.

Repairing Minor Gelcoat Cracks

1. Employ a rotary tool or scraping tool to open the crack into a "V" shape. You will need to go through the gelcoat to the fiberglass and open the full length of the crack. Next, use fourscore-grit sandpaper to scuff up the opening you created. Fold the sandpaper so you lot tin go a corner of it into the opened crack.
2. Afterward removing the dust, you can fill the cleft with G/flex® 655, Six10® or WEST SYSTEM 105 Epoxy Resin®/20X Hardener thickened with 406 Colloidal Silica Adhesive Filler.
3. After the epoxy has fully cured, wash information technology with water to remove any amine chroma. The blush is water-soluble, which means h2o is the best option to remove information technology. You tin now sand and apply a colour matching gelcoat to the area.

If the gelcoat cracks were acquired past fiberglass flexing, add some fiberglass reinforcement to the backside to help foreclose futurity cracks.

If a spiral pigsty repair has a fiberglass core behind it, seal the core with epoxy. With balsa or cream core, employ a bent nail to remove a small amount of core from behind the fiberglass, and then fill the expanse with 105/20X thickened with 404 High-Density Adhesive Filler. For plywood or other wood cadre, make an oversized hole and fill it with 105/20X and 404 High-Density filler. Both methods provide a good seal on the core and more than holding forcefulness for the fasteners. For greater particular on fastener bonding, read the Fiberglass Boat Repair & Maintenance manual's department on hardware bonding or visit westsystem.com/hardware-bonding.

Stress Dandy

These gelcoat cracks are stress cracks at the corner of a companionway.

A concentrated group of cracks mostly running in the same direction indicates a more than severe problem. This is often institute on the leading border of the cabin peak where it meets the deck. This can be the outcome of a loftier flex expanse enduring heavy seas or too much load on the boat. Cracks may also form at a bulkhead or other hard spots backside 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 surface area with a wet cloth so the cracks or fractured fiberglass will appear as white lines in the laminate.

Proceed until the fractured laminate is removed, then exercise a traditional fiberglass repair following these steps:

Grind out the area to a taper of 12 to 1 from the deepest point.

Cutting fiberglass patches starting with the largest offset, working your mode smaller to fill the area that has been basis away.

Using Due west Organization Epoxy, wet out the fiberglass pieces and apply them to the repair expanse, starting with the largest patch commencement and working your way to the smallest. Let the epoxy cure.

Launder the expanse with h2o and a nylon scrub pad to remove any amine chroma, and sand the repair off-white with the surrounding expanse. If in that location are low spots, thicken Westward SYSTEM Epoxy with 407 Depression-Density Fairing Filler and use information technology as a fairing compound to make full in low areas. Let the epoxy cure, launder information technology, and sand it to shape.

After concluding fairing, apply two coats of unthickened WEST SYSTEM Epoxy to seal the repair area.

Wash and sand the cured seal coat of epoxy then apply a topcoat of paint or gelcoat. See Fiberglass Boat Repair & Maintenance, pages xix-25 for detailed instructions.

Thermal Fatigue Gelcoat Cracks

Short, random cracks are called "crazing."

The environment can dramatically affect gelcoat. Wax tin can protect it from fading just there is no way to protect gelcoat against the repetitive expansion and wrinkle of temperature change. This movement tin can cause cracking, which may appear in a parallel or a random pattern.

Parallel patterned cracks volition vary in length from curt to several inches and are a few to several inches apart. I have heard them referred to equally old age cracks. Often these are caused by an expansion of the deck laminate, making the gelcoat more than susceptible to flexural stress.

Short, random cracks are also referred to equally gelcoat crazing. Crazing tin be localized to a small-scale area or completely encompass a deck. I have seen cockpit soles that remind me of a shattered car window. Crazing is caused by the gelcoat expanding and contracting over a given expanse.

Nosotros get customer calls asking if sanding the gelcoat and rolling epoxy over information technology volition make full the gelcoat cracks and forbid them from returning. Sadly, the answer is no. Cracked gelcoat should be removed. After gelcoat removal, sand the fiberglass laminate with 80-grit sandpaper. After sanding, make whatever needed repairs to the area. Roll on a minimum of three coats of West Arrangement® Epoxy to seal the fiberglass before applying a stop coat of pigment or gelcoat.

When gelcoat cracking is a symptom of another problem, repairing the crack and not repairing the underlying cause could pb to repeated keen. In the instance of a thick gelcoat, thinning the gelcoat is not applied.

After the repairs are completed, some boats remain crevice-costless for years. Taking your fourth dimension and doing the task correct will pay dividends in time and money.

Our Fiberglass Boat Repair & Maintenance transmission has illustrated instructions on many aspects of fiberglass boat repair, including gelcoat repairs. It's available for costless download in the instruction section on westsystem.com.

Source: https://www.epoxyworks.com/index.php/repairing-gelcoat-cracks/

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