Repairing small (<0.25") hole in fiberglass canoe

Was wondering what the best patch to “patch” this little hole (see pictures - $5 bill for scale). It looks more like the gel-coat got chipped off and the fiberglass is just exposed, but I don’t really know. It’s located about a foot below the gunwale (above the waterline) and don’t appear to go all the way through (found it by shining a flashlight on it). Any thoughts on how I might protect the fiberglass or at least prevent it from becoming something worse?


There are several methods, some more sophisticated than others, but this is the method I’ve used and am fairly satisfied with.
Flake out any loose material around the edges of the chip and rough up an area about 1/4 inch around the chip with sandpaper. Cut a piece of plastic slightly bigger than the area to be patched - I use the plastic backing from vinyl lettering material, but 6mil garbage bag will work also - anything that epoxy will not adhere to will work. (Test a piece separately and look for material that the epoxy will peel off of cleanly after drying.) Tape it horizontally about an inch under the chip so it hinges down and will cover the chip by an inch or two when hinged up. The idea is to fill the chipped area with epoxy, flip the hinge up, smoothing the fill to the contour of the hull, and finally securing it with tape around the outside to form a sort of mold to keep the epoxy from sagging while it sets up.
You can mix in a small (less than 10%) dab of acrylic artist’s color to match the hull. (Test and compare color before the final mix, of course. This takes a bit of fussing and rarely comes out a perfect match, but it will be better than the white spot that will show if you use no color.) As the epoxy ages it will tend to impart a yellowish hue of its own, but on a patch of this size, it would take a pretty serious inspection to find that flaw.
Use clear epoxy with a slower set time - 20min at least, - and add just enough color (if you choose to use it) to tint the epoxy. Don’t go for an opaque. Use just enough to fill the chip with the epoxy, flip the “mold” up", press it smooth with a putty knife or such, and secure the edges of the plastic with tape.
Mildly heating the area with a hair dryer before application speeds the cure and helps the epoxy saturate the underlying cloth, but it will work without heat.
Let the epoxy cure and remove the plastic. If there are some uneven areas around the patch, they can be carefully scrapped to close to smooth with a single edge razor blade or utility knife blade. Depending on how finicky you want to be with this you can then fine hand sand the patch and progress from ~400 through 600, to 1200 grit wet/dry sanding and finally buff it out with rubbing compound if you want.

Some folks use fiberglass resin (which I find hard to mix in small batches) instead of epoxy and that probably does make for a more flexible patch and might adhere better, but for something as small as this it shouldn’t matter much.

Hope this helps. I’m sure others will chime in with other methods.

It looks as if the damage is mostly to the external gel coat, but I do see some disruption of the fibers of the underlying fiberglass roving, so it would probably be better to put some resin on it rather than just trying to repair it with a polyester gel coat repair kit. The damage to the roving does not look bad enough to me to require any type of reinforcement with cloth, but I would push in on the hull around the area of damage to see if there is any unusual give suggesting more extensive damage than that visible in the photo.

Assuming there is no evidence of more extensive damage, I would go ahead and remove any loose gel coat at the edges of the damaged area, and use some sandpaper to feather the edges of the intact gel coat into the area of the void. I think many types of resin would likely work, but since you probably don’t know what type of resin was used to make this boat, I probably would not use a polyester resin. Polyesters may not cure properly when applied over epoxy or vinyl-ester resins.

Wax paper and Saran Wrap have also been used as a poor-man’s peel ply. I have found it hard to use them without getting wrinkles but for such a small area, they would probably work well. If you can prop the boat on its side so that the damaged area is horizontal, you can apply your resin over the exposed cloth with a small plastic spatula or squeege, then cover with whatever and smooth with your squeege. I wouldn’t worry to much if the material you use sticks to the resin. If it does, you can just sand it right off with fine sandpaper once the resin has fully cured. You might need to do a little wet sanding on the repair to get a completely smooth surface.

Rather than trying to tint the resin, I would probably plan to just paint it once the resin has fully cured. I suspect you could get a much closer color match using automotive touch-up paint, or whatever paint most closely matches the color of your hull. Paint can and does get scratched off, but a small area fairly high up on the side of the boat is going to be relatively protected.

I picked up some 3M 5200 fast cure to fill 'er in - that seemed to be the simplest and surest thing to do from what I’ve been seeing. Great stuff, looking forward to seeing how it turns out!

I had similar damage on the stern of my wildfire that I filled with gelcoat and covered with a fiberglass patch. if it is above the waterline I’d skip the fiberglass.

If you haven’t already applied the 5200, I recommend that you don’t. Yes, it will seal the area, but it will make it harder to repair later if you ever have to, since removing it will be a major pain.

5200 is fast and cheap but I would glue something on top of it even aluminum from a for sale sign or flattered piece of soda can overlapping the hole by 1/2". Masking tape over it till it sets. Not what I would do but to buy all the stuff you need gets expensive to make it a proper patch and much more time.

My question is, are you sure that is gel coat? It looks kind of thick and rough as a cobb. Could it be some kind of paint, or poly coating? It appears that no mat was used as the fabric next to the “gel coat.”

If it is at all possible to contact the manufacturer, that would be my first step to try to find out what resin was used and what type of coating. I think whatever type of repair you choose, it might be beneficial to wipe the repair area with acetone just prior to applying the repair.

I’m thinking that for a quick, strong permanent and simple repair, epoxy would do the job and just paint it with auto touch-up as has been suggested.

@magooch said:
My question is, are you sure that is gel coat?

If the question is for me, it is definitely gel coat. The hole was pretty big, so even with a mat it tended to run down the sides. I sanded it before putting on a strip of fiberglass. No problems yet.

@eckilson said:

@magooch said:
My question is, are you sure that is gel coat?

If the question is for me, it is definitely gel coat. The hole was pretty big, so even with a mat it tended to run down the sides. I sanded it before putting on a strip of fiberglass. No problems yet.

Sorry, my post was in reference to Joose’s original post. However, when I mentioned “mat”, what I meant was fiberglass matting–as opposed to cloth, or woven roving. I only mentioned it, because generally the gel coat is much less likely to telegraph cloth, or roving patterns through when mat is used under the gel coat.

It might be the magnification, but the underlying fabric looks like a coarse cloth, or woven roving and certainly not mat. And again, maybe due to the magnification, the finish is not smooth like a gel coat should be, but I suppose it might be from the mold.