Canoe Repair From the Inside Out

CanoeRapidsSo you’ve scraped your way down a rocky riverbed with your fiberglass canoe, which didn’t come out of the water the way it went in? Sometimes, watercraft adventure turns into watercraft abuse, and repairs are necessary. But don’t panic. Fiberglass repair does not require professional training or even a lot of time. With the right supplies and some elbow grease, you can do it yourself.

First things first, however: let’s assess the damage.

Just a scratch? Depending on the depth, that’s generally a simpler repair, approached in several ways. Shallow scratches can often be buffed out with polishing compounds. If scratches are deeper, consider using an epoxy filler. If they haven’t abraded the fabric below, try to carefully work epoxy resin into the cut. In this case, you may want to add a silica filler to your resin—this is a thickening agent that will prevent your resin from running on a slick or curved surface. Once cured, you can lightly sand and/or polish as necessary.

When the hull is heavily scored or broken, or when there’s a clear hole, your boat will require a patch. And while you’re at it, make it a double. By patching with fabric on both sides of your hull, you maximize its strength and, in some ways, minimize your effort.

1. Remove Damage


Conduct a simple test to determine the extent of the damage. From the outside, it may look like a small hole, but with enough force, a solid hit on the rocks can create damage within the layers of your hull. With the edge of a coin, or the grip end of a screwdriver, tap the area of impact: solid laminate will sound sharp (like a “ping”), damage (or delamination) will sound dull (like a “thud”). You may want to lightly mark the damaged area with a pencil or marker. And with a fine-toothed saw, remove the damaged laminate with a circular or oval cut.

2. Prepare the Surface

You’ll need to feather the inside edges of the hole by sanding. But before doing this, be sure to wash the area around the hole thoroughly with a solvent. The original fiberglass will likely have traces of mold release on the outer surface and wax on the inner surface. If you fail to remove the wax first, sanding can drag it into the bottom of the scratches and weaken the bond. Allow it to thoroughly dry.

CanoeSandingFrom the inside of the canoe, lightly feather the inner circumference of the hole with a rotary sander using medium-grit sandpaper. Sand the edges down to a wide, gradual angle so it forms a concave opening.

3. Mask and Mold

Although the bulk of the repair will be done on the inside of the watercraft, you’ll still need some minor prep work on the outside. Prevent resin runs from adhering to the exterior of the canoe with a coat of wax—avoid getting any on the inside, or even along the edge of the hole. You may even want to mask the area below the hole with tape.

Cut a scrap of thin acrylic (like Plexiglas) a foot larger than the hole (heavy-duty cardboard has been known to work as well). Wax this backer, then spritz it with PVA mold release. Tape the backer to the outer surface, so that it assumes the correct curve.

4. Fabric


The number of layers will be determined by the thickness of the hole; you need approximately one layer for every 1/32-inch. Cut the first layer of fabric just one inch wider than the hole, then subsequent pieces, each an inch larger in perimeter until you reach a piece one inch wider than the perimeter of the sanded area. The entire schedule of fabric should be cut before you begin the lay-up process. Once lay-up begins, layers should be applied largest to smallest, so as to maximize the area of the secondary bond.

Fiberglass canoes can be repaired using fiberglass fabric start-to-finish. However, to increase the strength of your repair, you can substitute one or more layers with Kevlar®. Remember, Kevlar cannot be sanded, so be sure Kevlar is used as an inner layer that will be covered with fiberglass.

5. Resin

Epoxy is a wise choice for canoe repair for several reasons. Compared to polyester and vinyl ester resins, epoxy delivers an edge for strength without adding significant weight. Plus, it has great bonding qualities. Epoxy requires a hardener in order to cure, so be sure to have adequate measurement and mixing supplies, like a cup and stirrer, on-hand.

6. Lay-up

WetLayUpFrom the inside of the canoe: Wet the inner surface of your outside patch with resin and lay-up your first two to three layers of fabric, squeezing out any air and excess resin with a roller or squeegee. Remember: add layers largest to smallest. Let these layers set, then add consecutive layers, three to four at a time, allowing them to set before adding the next section of layers. Adding too many layers at once will likely generate too much heat and “cook” your laminate, weakening it. Continue adding layers until your repair is flush with the interior surface. Allow to cure overnight.

From the outside of the canoe: Once the inner repair has cured, remove the patch taped to the outside of the hull. Sand an area approximately two inches wide around the perimeter of the hole; this helps to create a mechanical bond with the outer layer of fiberglass. Again, clean the area, making sure to avoid the hole. Wet with resin and apply one layer of fiberglass, removing any excess resin. Allow this layer to cure overnight as well.

7. Finish

Once both sides have completely cured, sand and feather both cover patches to match the hull. Finish to a silky smoothness using a 400-grit wet sandpaper. For the most part, just a couple layers of fiberglass will cure transparent. If you’ve used Kevlar as part of your inner patch, its color will likely be visible as part of the repair. For smaller repairs, this is an adequate patch, and your repair is complete.

RedShinyCanoeFor larger repairs, you may want to color-match your watercraft. With epoxy or vinyl ester resin, consider adding an opaque pigment to your resin when making your outer patch repair. And, keep in mind: most gel coats will not adhere to repairs made with epoxy resin, as most gel coats are polyester-based. If you intend to color-match your repair using a polyester gel coat, consider using a polyester resin to make the repair.

Allow a full 24 hours for any resin application to fully cure. Then you’re ready to hit the water.

You can find all the supplies you need to make canoe and kayak repairs at, including fiberglass boat cloth (in 6-, 7.5-, and 10-ounce weights), Kevlar fabrics (in yellow, blue, and red), epoxy resins and hardener, mixing supplies, and more.

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1 minecraft { 07.24.14 at 2:03 pm }

Way cool! Some very valid points! I appreciate you penning
this article and the rest of the site is also really good.

2 abowser { 07.25.14 at 2:00 pm }

Hope it gives you some new perspective on possible repairs. It never hurts to look at things differently! Thanks for the comment.

3 Rocky Langley { 08.20.17 at 3:54 am }

Question!: How can I tell if the scratches on the under side of my canoe need more than a filler job? Is a full on patch job usually only need if there is an apparent crack? Thanks for the article!

4 { 10.30.17 at 7:20 pm }

If you can see fiberglass or the scratch is deep into the fiberglass, a repair patch is needed. If the scratches are shallow and just at the surface, a filler or a sand and a buff would be needed.

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