How to Repair a Fiberglass Boat? Is It Possible?

Last Updated on March 9, 2021

Even the fiberglass boats that are only used once in a while suffer from spider web cracks at least. There’s nothing more disheartening than seeing scuffs and chips, holes, and cracks on boats for the boat owners.

However, due to its unique characteristics, you can DIY repair it! A splash of care and skills along with some resin and glass fabric can fix the worst hole you might get on your boat.

A large portion of boat owners assumes that self-repair is not all that durable and will not last for an ample amount of time. Well, this idea is entirely wrong, and you will be good to go if you follow only a handful of simple instructions.

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Repairing a Fiberglass Boat: Step by Step

Step 1: Chop Off the Damaged Parts

Delamination is one of the most common issues upon the impact of a fiberglass boat.

You can tell the damage done on the laminate by its sound; take the rear side of a screwdriver made of plastic, and if you hear a sharp noise by tapping over the area of impact, this means that the laminate is fine and solid. A muffled sound will indicate delamination to you.

Find the entire delaminated area, and just cut it away! Before that, do check on the inside to see if there are any obstructions. Saving damaged fiberglass is not a wise decision; we would change it with a brand new one.

Step 2: Work from the Inside

If the area of the impact is, as little as a 3-4 inch diameter hole and is beyond the waterline, then you should work from the inside of the hull.

If you try to work on the exterior, you will make a mess and will end up repairing an area 5 times larger than the original one. Working from the interior though will make your life a hell of a lot easier and stress-free.

Secondly, you should internally repair it because with a shiny and polished surface you will be able to back it from the outer side. Also, making a mold will let you lay-up the fix-up as it was initially gel-coated. You will not need to stress much about the finishing work then.

Step 3: Use the Dewaxing Solvent for Cleaning

The dewaxing solvent should be used to clean and rinse the area near the hole before getting into anything. Remains of mold release and surfactant will be visible on the original fiberglass of the internal layer. Failing to wipe out the wax will result in dragging it downwards to the scratches while grinding.


Step 4: Employ the Grinding Process

The laminate has a powerful chemical bond due to its original process of layering it up. However, the initial layer is not chemical; instead, it is mechanical.

Here is where grinding shows its cruciality for a solid fix-up.

To grind a 12-1 bevel close to the area of the inner side of the hole, load up the disk sander with a 36-grit disc. A rectangular perimeter should also be grinded above the angle to make room for the concluding layer of fabric.

How to Repair a Fiberglass Boat

Safety comes first, so be sure to cover up your face with a high-quality dust mask and goggles for your eyes. To avoid irritation, wearing a full-sleeved shirt might be prevention.

A smart thing to do would be tilting the sander to one side so that the dust is pushed in the opposite direction of you. You will see a very dull looking surface after brushing the dust away as well as wiping it with acetone soaked piece of cloth.

Step 5: Cut the Fiberglass Fabric

To match the hole, cut ample fiberglass fabric. If you don’t have a kind timetable, begin with two one and a half ounces mat layers, then switch up mat and 6-ounce cloth. The amount of laminates widely depends on how thick the hull is. You will need to apply a single layer for around 1/30 of an inch.

Cut out a larger piece of fabric for the initial layer, and then the following pieces will be an inch smaller in cuts. Apply the large piece of cloth first followed by the smaller pieces, so that a stronger secondary bond is created.

Step 6: Use Polyester or Vinyl ester Resin

Either polyester or vinyl ester resin can be applied for repairs beyond the waterline. You can pick up epoxy only for repairs to be done underwater, not for gel-coated surface repair.

While doing repairs with these two sorts of resin, what you will most definitely need is laminating resin.

The good thing about this resin is that it does not wholly cure upon exposure to open air. Hence a chemical bond is created between the many laminates applied. By using just plastic or even by brushing on (PVA) mold release for an airtight seal, your final laminate will be cured.

Step 7: Speed Up the Process with a Catalyst

Polyester and vinyl ester resin both require methyl ethyl ketone peroxide(MEKP) as their catalyst. MEKP and MEK are two completely different things, don’t be a fool and mix them up!

Around 1-2% of the volume of polyester will be needed, although it can vary.  Resin weighing about an ounce will be catalyzed by 1% by using four drops of hardener. The lay-up will be weakened if you don’t stir the catalyst throughout, also causing under cured resin.

The cure time can be adjusted a bit by varying the amount of catalyst you put in. The climate, temperature, and density of the laminate also have an impact on the cure time.

We would highly recommend you to test out the mixture. If it is hardening in around 2 hours, then it’s perfectly fine, and overnight hardening isn’t a problem either unless you have a rush. Make sure you don’t add excess resin, it can start to cook up and weaken the lamination.

Step 8: Apply Gel coat

You have come across the word gel coat multiple times in this article; it means polyester resin with some pigment. You will have to begin the fix-up by applying 20 mils of shade coordinated gel coat on the wax backer. Drag a toothpick along the surface to check the thickness (1/32 means 30 mils).

Step 9: Build the Layers

Brush wet polyester resin onto the gel coat just as it hardens. Layer up double layers of mat and then a single cloth, then squeeze out any bubbles by using a squeegee and a roller for the resin.

When you see the three layers have hardened, lay-up four extra layers. Do not make the grave mistake of layering more than four piles; it will produce heat from the resin and make the lay-up weak — progress by layering up to four piles until it is leveled with the inner surface.


After all the work is done, finish off the job by placing a rectangle piece of cloth followed by another larger piece. When these have been put on the patch, it should be smoothened out with the help of a squeegee before sealing it airtight with PVA or plastic.

From the outer area, remove the backer and then fix the flaws by filling in the tiny holes on the goal coat using gel paste. Wait for it to be fully cured, and then wipe the area clean, and after some sanding and polishing, you will be good to go!


We hope you found this article helpful and hopefully we were able to reduce the stress in your head. Abundant information has been provided in this article, so you shouldn’t face any more issues, but if you are still confused, feel free to drop down your question in the comments section below.

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