Fiberglass Boat Hull Repair

Fiberglass is forgiving right up until it isn't. It takes scrapes and dings without complaint, then a hard hit puts a star crack in the hull and suddenly you're looking at a layup job, a week of cure time, and a bill.

For gouges, punctures, and cracks in the skin, there's a faster path.

What you'll need

• Solar Patch — Medium (6"×9") or Large (9"×12") for most hull damage
• Scissors or a utility knife
• Sandpaper or a scuff pad
• A wax remover or degreaser, and a clean rag
• A UV Cure Light for shaded or evening work

Before you start: wax is the enemy

A well-kept hull has been waxed, polished, and treated. Every one of those products is designed to stop things adhering to the surface — which is exactly the wrong property when you want a patch to stick.

Remove the wax first, then scuff the area to a matte finish. You're going about two inches past the damage in every direction. The surface should look dull, not glossy. Then clean and dry it.

An older hull that hasn't seen wax in years has a different problem: oxidation. Chalky, faded surface material. Same fix — scuff it back until you're on sound material.

Step by step

1. Trace the crack. Fiberglass stress cracks radiate. What looks like a two-inch star is often a six-inch crack pattern under the surface. Look at it in raking light and follow the lines to where they end.
2. Cut the patch to cover all of it plus about an inch of sound hull in every direction.
3. De-wax, scuff, clean, dry. In that order. Scuffing before de-waxing just grinds wax into the surface.
4. Peel and apply. Press from the center outward, working the patch into the hull's curve. Fiberglass hulls have compound curves — take the extra few seconds to get full contact rather than letting the patch bridge.
5. Cure 5–10 minutes in direct sunlight, or use a UV light.

Once cured it can be sanded and painted if you want it to disappear into the hull.

Common mistakes

• Skipping the de-wax step. The most common reason a hull patch fails, and the easiest to avoid.
• Underestimating the crack. Fiberglass damage extends past what you can see. Raking light shows you the rest.
• Patching a hull that's still in the water. Dry surface required.
• Sanding before the patch is fully cured. Give it the full cure, then sand.

[FROM THE SHOP — your anecdote here.]

When this won't work

• Structural or through-hull damage. Damage that penetrates the laminate, compromises a stringer, or leaves the hull flexing needs a proper layup by someone who does it professionally.
• Below the waterline while in the water. The patch holds below the waterline once cured — but the repair has to be made dry.
• Delamination. If the layers are separating, patching the surface doesn't address it.
• Anything pressurized.

How long it lasts

Cured Solar Patch is rigid, waterproof, rated to 200°C dry and 90°C wet, and Class 1 fire rated to ASTM E84-18. It can be sanded and painted once fully cured.

Related guides: How to Repair a Hole in an Aluminum Boat · Marine Repair

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