How to repair a fibreglass canoe (on a trip and at home)

by | Jul 17, 2022 | Paddling

This post may contain affiliate links.

We’ve had our 16-foot fibreglass Prospector for two years now. In that time, we’ve put as many as 10 cracks and holes in it. You could say that we’ve gotten pretty good at figuring out how to repair fibreglass canoes—both temporarily while we’re still out canoe tripping and more permanently when we get back home.

One of the best things about having a fibreglass canoe is that it’s relatively easy to fix. The trade-off, of course, is that it’s not quite as durable as some other types of canoes, like those made out of Kevlar or Royalex/T-Formex.

What is fibreglass, anyway?

Fibreglass is a material made from glass fibers that are woven into a cloth, much like how cotton is woven into a t-shirt. The cloth is then soaked in a resin, which hardens and bonds the fibers together.

Most canoe hulls are made out of three layers of fibreglass. The inside and outside layers are called the “skins” while the middle layer is generally just referred to as the “core.”

The skins are generally made out of chopped strand mat (CSM), which is just a fancy way of saying that the glass fibers are all different lengths. The core, on the other hand, is usually made out of continuous roving, which means that the glass fibres are all the same length.

Continuous roving is generally considered to be stronger than chopped strand mat, which is why it’s used in the core. However, it’s also more expensive, so most canoe manufacturers use a combination of the two.

Why do canoes crack?

A crack in our canoe.

The most common reason that canoes crack is because they’re exposed to sudden changes in temperature. For example, if you leave your canoe out in the sun all day and then take it for a paddle in cold water, the hull will expand from the heat of the sun and then contract from the cold water.

This repeated expansion and contraction can cause small cracks to form in the hull, which can then lead to larger cracks over time. And obviously, canoes can crack if they’re dropped or hit against something hard—like rocks.

Funny enough, none of the cracks or holes we put in our canoe were made by bashing into rocks while running whitewater rapids. The first few cracks we found were from strapping the canoe down on the top of our vehicle too tightly, which weakened the hull and caused it to crack.

Another crack came from lifting the canoe over a beaver dam when it was loaded with lots of heavy gear. We were trying to be careful, but the added weight put too much stress on the hull and caused it to crack.

And finally, we put one big hole in our canoe when we left it in the water at a campsite (tying it with a rope to a nearby tree) and not realizing that the waves would repeatedly smash it into the jagged rocks that lined the shore.

How to repair a fibreglass canoe while out on a trip

A temporarily repaired canoe while out on a trip.

If you’re out paddling and you suddenly find yourself sitting in a pool of water, chances are there’s a crack or hole in it somewhere. If it’s small, it may not be obvious where it is.

Your first goal should be to get to shore as quickly and safely as possible. If water is pouring in at a fast rate, you may need to bail it out while you and your canoe partner paddle. This is why you should always have a canoe bailer with you.

Once you’re on shore, you have two good options to temporarily repair any cracks or holes in your canoe so you can finish your trip. These two options are:

  1. Duct tape
  2. Epoxy putty

We’ve used both. Here’s what you need to do.

The duct tape method

Temporarily patching the canoe with duct tape.

I know what you’re thinking. Duct tape? Really? Yes, really.

When we took a whitewater canoe training course with expert canoe tripper Hap Wilson, he swore by the stuff. I don’t think he even mentioned the epoxy putty. Why bother when something that’s commonly found in most households gets the job done as good—if not better?

We recommend bringing at least half a roll of duct tape. You can even pop the inner cardboard roll out of the roll to compress the roll of duct tape and save space.

Step 1: The most important thing to ensure that the duct tape method will work is to make sure the canoe is very dry. If you have time once you reach shore, allow your canoe to sit in the sun and dry out for a while.

If you’re in a hurry, use a towel to dry it off as much as possible. Ideally, you want to both the inside and outside of the canoe to be completely dry.

Step 2: You’re going to put duct tape on both the inside and outside of the canoe at the site of the crack or hole. Start by tearing off a piece of duct tape that’s big enough to cover the crack or hole on the outside. It’s better to have too much than too little.

Step 3: Apply the duct tape to the crack or hole, making sure to apply firm pressure and smooth it out as you go. You don’t want any air bubbles.

Step 4: Once the duct tape is in place, tear off another piece of duct tape and use it to reinforce the first piece by applying it perpendicular to the first piece. This edges of this layer should overlap the layers of the first layer. Use one to two more pieces to complete the second layer.

Step 5: Repeat step 4 for a final layer. You should now have three layers of duct tape—all overlapping the edges of each previous layer to keep as little water as possible from seeping in.

Step 6: Repeat steps 3 through 5 now on the inside of the canoe.

We used the duct tape method on a hole that was big enough to see right through our canoe. It worked like a charm! Our duct tape patch was able to withstand about six hours worth of paddling with very little water getting through, which was enough to allow us to enjoy the rest of our canoe trip and get back home safely.

The epoxy putty method

Repairing the canoe en route with some underwater epoxxy putty.

You can get epoxy putty sticks from Amazon or any hardware store. These are basically sticks of hardening epoxy that come in a tube. The great thing about them is that they’re small, compatible with fibreglass (in addition to a variety of other materials), and effective even when used on wet surfaces or underwater.

You should really just follow the instructions on the epoxy putty stick package that you get, but in general, here’s what you’re supposed to do.

Step 1: Put on a pair of protective gloves and use your fingers to break off a piece of the epoxy putty stick. The piece should be big enough to cover the crack or hole. You may need more than you think to get a good coverage.

Step 2: Knead the piece of epoxy putty until it’s soft and pliable. You can do this with your hands while wearing the protective gloves, or you can use a hard object like a spoon or a stick.

Step 3: Once the epoxy putty is soft and pliable, apply it to the crack or hole. Be sure to apply firm pressure and smooth it out as you go.

Step 4: Allow the epoxy putty to dry and harden according to the instructions on the package. It can take as little as five minutes for it to set, but you’ll probably want to wait at least 30 minutes for it to full cure and harden.

We’ve used the epoxy putty method in the rain when we still had a ways to go to get to our campsite. Unfortunately, we didn’t think to bring protective gloves to be able to knead it with our hands, so we had to improvise with a piece of wood we found on the shore.

We couldn’t wait for the epoxy to fully harden, but it held up alright as we paddled a couple more hours to get to camp. By the end of the trip, chunks of it were falling off.

Out of the two methods, we think the duct tape method is the easiest and most effective. After all, it’s only temporary.

How to repair a fibreglass when you’re back at home

Getting ready to repair the canoe back at home.

Once you’re safely back at home with your patched canoe, the real fun begins! It’s time to stock up on supplies, clear some space in your garage/driveway/yard, and get to work.

What you’ll need

  • Face mask (optional, but good to avoid breathing in fibreglass dust)
  • Safety glasses or goggles
  • Electric angle grinder (optional, but highly recommended)
  • Electric sander
  • Fibreglass or epoxy resin
  • Liquid hardener
  • Fibreglass cloth
  • Mixing tray and stick
  • Small paint brush
  • Scissors (sharp ones)
  • Acetone or lacquer thinner
  • Rag, cloth, or paper towel
  • Latex gloves
  • Parchment paper
  • Painter’s tape
  • Paint (the colour of your canoe, fibreglass friendly)

You can find the resin, liquid hardener, fibreglass cloth, and paint at many marine and boat stores. Brace yourself—these supplies don’t come cheap!

Be prepared to spend at least a couple hundred dollars on this stuff, not including the grinder and sander. The good news is you’ll have them already if you find any additional cracks or holes in your canoe in the future.

First things first: Make sure your canoe is positioned properly so that it doesn’t wobble around or feel as if it’s going to slide off something. In most cases, the best thing to do is just lay it flat on the ground.

To start, we recommend turning it over so the hull is facing up.

Step 1: Grind away as much of the damaged fibreglass as possible

Grinding away the damaged fibreglass on the canoe.

You’d think that making a crack or hole any bigger than it already is would be a bad thing, but in the case of fixing a fibreglass canoe, this is exactly what you need to do! (Hey, that rhymes.)

Use an electric angle grinder with a sanding disc to remove any loose fibreglass and create a smooth surface—even if that means putting a huge hole in it. Any damaged fibreglass that isn’t removed could problems for the strength of your patchwork.

Step 2: Sand the area until it’s smooth

Sanding the canoe so it's smooth.

After you’ve ground away all of the damaged fibreglass, you’ll need to sand the area until it’s as smooth as possible, including the edges of the paint around the hole.

You’ll actually want to completely sand the paint away so there’s no paint for a good inch or two around the entire opening of the hole. The reason for this is because the the fibreglass cloth won’t adhere to the painted surface surface.

Step 3: Repeat steps 1 and 2 on the inside of the canoe

Repeating the process on the inside of the canoe

Flip the canoe over and do the exact same on the inside of the canoe. Remember, the key is to grind and sand away all the damaged fibreglass and a good 1 to 2-inch ring of paint around the opening of the hole.

Step 4: Clean the area with acetone or lacquer thinner

Cleaning the canoe with lacquer thinner.

Once you’ve sanded everything down and both sides of the hole feel completely smooth, it’s time to clean the area with acetone or lacquer thinner. This will help the resin and hardener adhere better to the canoe.

Take a rag, cloth, or paper towel and soak it in acetone. Rub the area until it feels completely clean and dry to the touch. Do this on both the outside and inside of the canoe.

Step 5: Cut the fibreglass cloth to size

Cutting the fibreglass cloth.

Take the fibreglass cloth and use the scissors to cut a small piece that fits just over the edges of the hole. This first piece will be your smallest, just to cover the opening. Don’t worry—you’ll be putting larger pieces of cloth over it in later steps.

Depending on the size of the hole, you may only need to apply a few pieces of cloth per side of the canoe. For bigger ones, you may need several more. Use your own judgement as you proress through these steps to decide how many layers of fibreglass cloth you’ll need to apply to make the patch as strong as possible.

Step 6: Mix the resin and hardener together

Getting ready to mix the resin and the hardener.

First, put on your latex gloves. It might also be a good idea to be wearing old clothes just in case you accidentally spill any of the mixture while mixing or applying it to the canoe.

Follow the instructions on the container for mixing the resin and hardener together. The ratio can vary depending on the brand you’re using.

The resin and hardener we bought were made to be used together and came with convenient pumps. Find it here on Amazon. This made it easy for us because the mix required one pump of resin with one pump of hardener.

Pour the resin and hardener into the mixing tray and use the mixing stick to stir them together according to the directions.

Step 7: Apply the small piece of fibreglass cloth to the hole

Applying the fibreglass cloth to patch the hole in the canoe.

Using one hand to keep the small piece of fibreglass cloth in place over the hole, use your other hand to apply the mixture with the brush over it so that it adheres to the canoe.

Now this is important: You want to dab the mixture to adhere the cloth to the canoe—not brush! Brushing will cause the fibreglass cloth to break up and create a weak patch.

Dab the mixture over the entire patch and all edges to adhere it to the paintless ring around the canoe. It should be fully soaked before moving onto the next step.

Step 8: Repeat step six with as many layers of fibreglass cloth you plan to apply

Continue applying more fibreglass cloth.

For the next patch of fibreglass cloth, you’ll want to cut a slightly bigger one so that it completely covers the first patch, and then some. Each patch of fibreglass cloth should get progressively larger so that it completely covers the previous patch.

We usually put three layers of cloth on each side of the canoe (for a total of six), which proves to be strong enough for the holes we’re patching. But remember, depending on the size of the hole, your canoe might require more.

The general rule is: the bigger the hole, the more layers of fibreglass cloth you’ll need.

If the edges of the cloth are long enough to stretch to the painted part of the canoe, don’t bother applying the mixture to adhere those parts, because they won’t stick well once it’s dry. You can cut or sand those pieces away later.

Also, don’t expect it to look very pretty. You just need it to be strong. You can always make it look better after it’s fully dry.

Step 9: Tape a piece of parchment paper to the area to protect it

Parchment paper used to protect the patch on the canoe.

You’ll be able to peel the parchment paper right off no problem once it’s all set and dry. This will just help protect the area while you move the canoe around to get to work on the inside area.

Step 10: Turn your canoe over and repeat steps 5 to 9 on the inside

Applying fibreglass cloth to the inside of the canoe.

It may be a lot of work to patch both sides, but it’s necessary to make sure that your canoe is as strong as possible.

Step 11: Let the mixture dry for at least 24 hours before taking it out on the water or painting it

Red paint to finish the job.

You might be able to get away with waiting less time if it’s warm and sunny out, but we recommend giving it a full day so that you can be sure it’s completely dry before using your canoe again.

Canoes don’t exactly look the nicest right after they’ve been patched, but you can make it look a lot better with a little extra sanding and some paint.

We use Pettit EZPoxy polyurethane topside paint in fire red for the outside of our canoe. We don’t bother with the inside since it’s not as visible, but you can paint that too if you want (and can find a matching paint colour).

Now you know how to fix cracks and holes in your fibreglass canoe!

Once you get the supplies and do it at least once, it’s pretty simple to patch a canoe. We hope you don’t have to use this information often, but if you do, at least you know how!

If you want to avoid patching altogether, be sure to take care of your canoe and inspect it regularly for any cracks or holes. A little bit of preventative maintenance goes a long way.

Happy paddling!

Popular posts

About Us

Elise & Ross

We’re Elise and Ross, avid backcountry campers and outdoor adventurers! We started Gone Camping Again as a way to share our knowledge and experience about wilderness living and travel. Our hope is that we inspire you to get outside and enjoy all that nature has to offer!

Read more about our story.