How to fix fiberglass canoe holes?

I’ve been looking for a first canoe for a while now and my uncle actually ended up having an old Sears and Roebuck 16’ free spirit fiberglass he ended up giving me. Now it was used for hunting and river floating so it has taken some good holes on the keel that I need advice on how to fix the holes and damage, I’d like to patch it up and then remove the camp and repaint it. Any advice is greatly appreciated!

Pictures of damage

short answer
To fix holes in a fiberglass canoe you will use fiberglass cloth, along with some type of resin.

I, like most other backyard canoe repair folks these days, use an epoxy resin which should bond to the canoe regardless of what type of resin was used in its construction. There are all types of structural fabrics you could use instead of fiberglass such as aramid (Kevlar), carbon fiber, Dynel, etc, but for a boat of this generally quality plain, old E fiberglass makes the most sense and is probably the easiest to work with. I would suggest using plain weave fiberglass cloth of 6 ounce per square yard weight.

You will need to use multiple layers to repair these holes to adequate strength. If the interior of the holes is accessible I would use about three layers inside and three layers outside, cut to concentric sizes in such a way that the fibers are aligned in different directions to each other and the keel line.

If you have never done any fiberglassing, a good on-line, free reference is System Three’s epoxy book which you can find here:

Read the sections that are pertinent to your repair.

first step
It looks like you’ve got a whole lot of trimming to do to start with. Not to worry, though–take it one step at a time and one area at a time.

Here is an article that might be helpful.

Fiberglass isn’t the easiest material to damage, but it does happen. Don’t be disheartened — the situation probably isn’t as bad as you think. There is no fiberglass damage that can’t be repaired.

The first thing to do is survey the extent of the damage. Is it superficial or structural, minor or major? Perform a visual inspection inside and outside of your kayak. If you see white stress lines in the fiberglass (inside), it is structurally damaged.

It is possible to get cracks in the gel coat finish without any real structural damage. Most gel coats are polyester based and brittle, but many kayaks (like NC Kayaks) are now manufactured with vinylester resins, which have much more flex than polyester gel coats. So the fiberglass can actually flex more than the gel coat without sustaining any damage.

Once you establish what needs to be repaired, we can determine what needs to done.

For gel coat cracks

Sand the cracks all the way to the fiberglass.

Mask off around the area to be repaired with masking tape.

Gel coat consists of three parts: the gel coat itself, a catalyst, and a surfacing agent to aid in the curing process. The surfacing agent is required for open-air cure of the gel coat. In place of a surfacing agent, you can seal off the repair with wax paper or plastic film. This keeps air out to allow the gel coat to cure completely.

Apply your gel coat with a brush. Try to apply it as smoothly as possible. This will save you time on sanding after it has cured.

After the gel coat has cured, it’s time for sanding. Start with a 400 grit sandpaper and sand the repair nearly flush. Try not to sand too much around the surrounding areas, as you can sand through that gel coat! You can mask them off to help prevent that. Wet sanding works best. Gradually work to finer grits (600, then 1200) before finally buffing it finished.

For fiberglass repair

A good rule to follow is for every inch of damage there needs to be 12 inches of repair, a 12-to-1 ratio. If the damage is a puncture, hole, or delamination, remove the damaged area by getting rid of any loose material. If the damage is only stress lines you can simply repair over them.

If you are using the woven roving, one ply each of mat and roving is usually sufficient. If you are using cloth you will need two plies of cloth and one ply 1½ ounce mat.

Prepare the fiberglass by cutting some mat to fit and fill the hole. Also cut some the size of the repair 12-to-1 ratio. Cut the cloth or roving just slightly bigger than the mat.

Rough up the area to be repaired with sandpaper — 120-220 grit is preferred — this aids in bonding.

Clean the area to be repaired with acetone. This removes any contaminants and also reactivates the existing resin to help with adhesion.

Back up the existing hole on the outside of the boat with cardboard coated liberally with wax or plastic film. This helps to keep the proper shape of the kayak exterior.

You are now ready to laminate. Mix your resin and catalyst per manufacturer’s instructions.

Install the mat in the hole. Wet out the mat and the entire repair area with the resin using a brush.

Add the first ply of mat. Apply more resin to the mat. Roll with a small paint roller or fiberglass roller to remove any trapped air.

Add the next ply, cloth or roving and apply more resin. Lightly squeegee to remove any trapped air. Apply subsequent plies following the same procedure.

After the resin cures, sand any rough edges.

Now it’s time to repair the gel coat using the process above.


Resin. Please note which type of resin you choose to use. Epoxies bond to everything, but polyester and vinylester resins will not adhere to epoxies. Try to use the same type of resin the kayak was made from (vinylester for NC Kayaks).

Catalyst. The resin you purchase will generally have a recommended list of catalysts, most commonly an MEKP.

Gel coat. Trying to match color can be frustrating. UV rays can fade colors over the years, and even “white” may not look the same from manufacturer to manufacturer. Our advice is to try to be as close as possible, but accept that it probably won’t be perfect.

Surfacing agent or wax paper / plastic film.

Acetone. This is commonly sold as nail polish remover, but that often has artificial coloring and odors added.

1-2" paint brush, depending on the size of the repair.

1½ ounce fiberglass mat.

Either 6-ounce fiberglass cloth or 18-ounce fiberglass woven roving. The roving will build up thickness quicker than cloth. The 6-ounce will give a cleaner looking repair. Either will give a strong finished product.

Small paint or fiberglass roller.

Plastic squeegee.

Sandpaper in various grits.

Buffing compound.

Warnings / Tips

Find a warm dry environment. Sixty-five degrees is the minimum temperature you should attempt to do a repair in. But the higher the temperature the shorter your work time is.

Wear appropriate safety equipment, especially disposable gloves. Resin and gel coat are impossible to remove from clothing once cured. They can surely hurt your skin too. A paper towel with acetone — while it will dry your skin — will help remove drops.

Mask, mask, mask! You can save yourself a lot of headache by preventing drips, overzealous sanding, and errant brushing from causing problems by masking off nearby areas.


– Last Updated: Jul-18-16 3:10 PM EST –

Thanks for the replies! I've been doing some research on repairs today. From what I gather I need to cut out the old busted fiberglass and then starting inside lay in fiberglass matting and dab it with resin, let it dry up and then put a piece of cloth of it and do the same. Then flip it over and on the outside cut pieces of cloth to the size of the hole I cut and do 3-5 layers, then let it dry, sand, body filler and paint? Or do I want to start outside and then put the new glass layers on the inside?

Or am I making it more complicated than needs be?

Namely, I was watching this two part video as it appears to be almost identical to mine with similar damage to the keel.

As a side note, in terms of PPE while working on this. Obviously nitrile gloves, goggles, long pants/shirt. As far as inhalation protection? Dust mask or full respirator? All repairs are done outside in the backyard.



– Last Updated: Jul-19-16 8:19 AM EST –

The videos were not too bad, at least the first one.

Note that the person doing the repair was using polyester resin, not epoxy. Polyester resin is cheaper and some consider it easier to work with as it is less viscous. But it is not as strong as epoxy and polyester resins will not reliably cure when applied over epoxy. The filler that he used was also a polyester resin based product like Bondo and should not be used over an epoxy-based repair.

If you need to use a filler to achieve a smooth and fair surface, you can use epoxy thickened with a fairing compound or silica powder. Epoxy additives are covered in "The Epoxy Book" which I already cited.

You don't need to use mat or roving. You can if you want to, but neither is as strong as woven fiberglass cloth and it would be one more thing to buy. As you can tell from the video, the fibers in mat are very short. Multiple layers of woven fiberglass cloth with the fibers aligned at different angles will provide a stronger repair for no more effort.

It seemed to me that the guy in the video may have debrided somewhat more of the hull material in the first video than I would have, but I was not there so I can't be sure. You should certainly remove any loose material and I would cut away or grind away any 'glass with obvious fractures. When laminating cloth you want to be sure that you are bonding to fibers, so sand down until you can clearly see fibers. Try to bevel the edges of the repair so that your cloth lays down smoothly.

For a through and through hole like this I would recommend at least 4 layers of cloth but for a very high wear area like the keel, I think 6 would be better. Your lamina should be cut at varying biases and should be concentric in size. I would have the smallest patch overlap the edges of the break by at least an inch, the next by 2 inches, and the next by three inches, for example. To be able to feather and smooth the edges of your patches, it is best to apply the largest patch first and go down in size. That way you will be able to sand smooth the edges of the smaller patches without sanding through fibers of the larger ones.

If possible, you will get a stronger bond if you apply each successive patch while the epoxy of the preceding patch is still "green". If you have to wait until the epoxy is completely cured, you will need to wash it before applying the next patch to remove something called "amine blush".

You can do the inside repair first, or the outside, whichever is easiest. You would like to have the exterior as smooth as possible. The interior does not matter as much if it is a bit rough or irregular. For a through and through hole you will need to create some sort of "epoxy dam" on the side opposite to that you are working on when you apply the first patch. I have used plastic packing tape for smaller defects. For larger ones some thin, flexible, transparent plastic sheet of the type that used to be used with overhead projectors might work.

The material that was shown in the second video and applied as a stem skid plate was not Kevlar 'cloth' as was stated. It was Kevlar felt, a widely used but crappy (in my opinion) material for that purpose.

I agree with the guy in the video that working with resin and fiberglass is really pretty easy. The first time you might get frustrated when the cloth frays or snags. Mix up your epoxy in small batches so that it does not "kick" too quickly. You can apply epoxy in a bunch of different ways, using a cheap chip brush (as shown in the video), a disposable foam brush, dripping it on and smoothing it with a plastic squeege, spooning it on and smoothing with a plastic stirring stick, etc. A foam roller works well on large surfaces, but I don't think that will apply to your repair.

More thoughts.
Awesome, thanks for the advice and insight. Do you recommend any particular type/brand of epoxy? Where can you typically source it at locally? The portion of the keel that needs to be repaired is easily a foot and a half long, should I cut the entirety of that section out and try to reshape it as best I can?

Lastly, in discussing it with you it sounds like it’s going to be best to lay a single piece of FG cloth on the outside and then lay my multiple layers on the inside, then sand down the outside to even everything out, is there a trick to cutting out the bad parts? I imagine it’s probably best to avoid cutting hard shapes like squares and I should try to round it all, any other thoughts?

I personally prefer West Systems epoxy. I have never had any problems with it. It tends to be a bit more expensive but West has excellent customer support. You can find a wealth of information including technical bulletins and tutorials on their website, and every time I have called their technical support I have reached a real, live human being who knew what they were talking about.

I have also used MAS and System Three epoxies with good results.

I know of a lot of people who swear by Raka epoxy but I have not used it:

Jamestown Distributors has now introduced a line of epoxies with properties that are said to be similar to West epoxy at a slightly lesser cost:

There are also many videos and other instructional materials regarding lamination and epoxy use on the Jamestown site.

Personally, I would not cut away anything that was not broken or damaged. If you have very sharp or irregular edges left after debriding the damaged materials you might round them off a bit. Those edges will be covered inside and out after your repair so they won’t make any difference. The more you cut or grind away, the bigger the defect you will have at the end. The bigger the defect the harder it will be to restore the normal contour of the hull.

hull repair
I am guessing without a photo, but you can probably repair dings around the keel with epoxy thickened with sawdust or a material like microballoons. It will be like working with peanut butter and can easily be spread with a putty knife. After the epoxy sets you can sand it smooth and paint it. For larger holes, fiberglass cloth on both sides and epoxy.