How to I go about repairing so pretty serious fiberglass spidercracking

Hello paddlers,
I have a fiberglass kayak (Cape Horn 17 Pro) about 15 years old made by wilderness systems. I bought it last year, seeing it has gel coat cracking all over the boat, but much worse on the left side on top of the deck. Lots of cracking in the paint and given it is significantly weaker than the opposite side, I’d say the fiberglass underneath is probably separating or no longer good. the repair area is going to be a little over a foot long. I think I have a good idea of what steps I need to take to repair it, however I wanted to see if someone could read over the steps I am going to take and correct me if any of them seem wrong. So here it goes.

I am planning to cut out the entire area with fiberglass separation, then I will be sanding down the edges to round them out. I will take making tape and run it over the hole on the outside of the boat. I will then be using whatever woven fiberglass cloth I can find and lay up 2 layers with epoxy fiberglass resin. I will remove tape and allow to cure, afterwards I will sand it down and apply gel coat over it.
The main part I am not sure on is how many layers of fiberglass cloth I should use, because this surface is also curved, I wasn’t sure if there was anything better than masking tape to get the curve correct, I wasn’t sure if I should possibly make a quick mold of the outside before cutting anything out. Also, say if only the outside fiberglass layers are cracked, could I potentially just sand down until Ive just got a thin inside fiberglass layer and just lay another cloth over it?

Thanks, any advise is greatly appreciated!

When you say “cracking in the paint” I presume you mean cracking in the gel coat. Gel coat is a pigmented polyester material.

You are going to have to remove the gel coat over the area and see what is underneath. Until then you can only guess as to what the repair will require. I would do that and take some photos and post them.

Assuming there is damage or delamination in the underlying structural fiberglass I would debride or cut out only fiberglass that has obviously disrupted fibers or has delaminated. I would leave whatever you can, if nothing else to maintain the shape of the deck and act as a mold onto which you will lay new cloth.

You will need to remove the gel coat from the intact undamaged deck adjacent to any areas you plan to lay new fabric onto, as you will want this to extend at least 2" onto undamaged deck.

Thanks for the reply! Yes I was referring to gel coat, Ill be sanding off the gel coat next week so I will make sure to come back with pictures, but I would say I am certain the fiberglass is damaged underneath as i can see some of it through the cracks in the gel coat, in addition to the fact it is noticeably weaker than it should be

Remove what needs to be removed and leave what doesn’t. If there are one or more reasonably clean cracks through the 'glass but the layers have not delaminated, and the edges of the cracks can be re-approximated, it is often better to just patch over the cracks rather than cut out a large area. I would do at least the initial patching from the interior of the hull if the area is accessible.

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Put two layers of mat inside after sanding it with 60 grit. Then work on the outside sanding that and see what’s up. Even if you sand most of the old glass away where damaged you’ll have something below to work with. Easier than cutting a piece out feathering the edges inside and out and closing a hole.

Have you ever done any body work or glass repairs before?

I have don’t glass work on my old canoe, but it had a thick compressed fiber layer so I really only did patching work. Why is it that I would use fiberglass mat? From what Ive heard woven cloth seems to be lighter and stronger.

Cloth is good but mat will give you more stiffness. More if you sand from the outside in. I did a few of my kayaks below the seat area with mat. I was on a kayak roller launch and was careful going out with my Current Designs Extreme. Coming back I pulled myself and hull back up. Then I heard a bad noise. When the kayak got to a point with me in it where it see sawed. Few cracks in the gel and glass was soft. I removed the seat and did two layers of mat one shape smaller to kind of feather it.

I did my other boats also because when in pull them off my floater into the bulkhead at low tide there’s a lot of pressure. Right when I get to the cockpit area it’s a pivot point. Seats out because I put wide base 17" seat in my kayaks. Yes kayaks gain two pounds or what ever it is, so 50 now instead of 48 lb. He’ll I’m 6’ 230 so it doesn’t matter much.

I would not cut out the bad section, but leave it to retain the shape of the hull and epoxy over it with some cloth in at least two layers.

You may be able to improve the cracking or glazing with some sanding and then adding a layer of epoxy and some paint.

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I have not done the work you are talking about, but one of the sea kayaks has had a repair for an issue that went down to the glass.

What weakened the glass in your boat may have been less a crack and more it getting wet because someone kept paddling it with the deep gel coat crack or left it so outside not being under cover. The glass repair was performed from the inside of the boat and the gel coat subsequently redone. Much more nicely sanded etc than I have ever bothered with my spot repairs but I lack patience.

Good luck!

Fiberglass cloth is stronger than chopped strand mat. Mat is thicker than fiberglass cloth. Since rigidity is primarily a function of thickness, mat will provide more stiffness per layer than cloth. But mat has a higher density and a lower strength to weight ratio than cloth, and you can achieve the same degree of thickness and rigidity by simply using more layers of woven cloth. If you do use multiple layers of cloth, cut the patches so that the fibers run at different angles so as to maximize the number of fiber crossings for maximum strength.

I would not use mat for several reasons. First, it is not as strong. Second, assuming you are going to need to apply at least one layer of fabric externally you will get a much better cosmetic result using woven fabric on the exterior. Using mat on the interior would require you to purchase two different types of fabric, unless you already happened to have mat on hand. Third, and most important, many if not most varieties of chopped strand mat are incompatible with epoxy resins and can only be used with vinylester or polyester resins. That is because the randomly oriented strands of fiberglass in mat are held together with a binder that requires styrene to break down the binder and allow complete resin penetration and saturation. Epoxy does not contain styrene and thus will not penetrate the mat effectively.

The best single material to use is S fiberglass which has 20-30% greater tensile strength than the common E fiberglass. It will work very well on both interior and exterior patches. If you happened to have some aramid fabric or could borrow a small amount, you could use it for interior patch work but I would not use it on the outside. If you find that you do need to do structural repairs and don’t already have materials on hand, I would order plain weave S fiberglass cloth in a 6 ounce/square yard weight and some type of epoxy resin.

You can buy S fiberglass from Sweet Composites:

Style 6533 is what you would want and a couple of yards (one 72" x 60" piece) will likely be more than enough to complete your repair and will allow you to cut patches at biased angles.

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You have no idea how helpful this response is, I guess I will have to do some research more about how fiberglass works but I will pick up some of the stuff you recommended. Thanks for the advice!

How do you use a fiberglass mat and resin?

Pour a small pool of epoxy resin /hardener near the center of the cloth . Spread the epoxy over the fiberglass cloth surface with a plastic spreader, working the epoxy gently from the pool into the dry areas. Use a foam roller or brush to wet out fabric on vertical surfaces. Properly wet out fabric is transparent.


WEST SYSTEM Epoxy › applying-…

Applying Fiberglass Cloth & Tape - WEST SYSTEM Epoxy

I’m wondering what is wrong with using polyester resin? Vinyl ester is better, but a lot more expensive and it has a very short shelf life. My question is related to the use of fiberglass mat. Mat works best as the final layer (just below the gel coat) so that there is little to no telegraphing of the thread patterns as with fiberglass cloth.

But I guess there is more than one way to skin a cat, or a composite kayak.

Polyester resin is generally fine, but epoxy is a bit stronger/stiffer and a better adhesive. Some people claim epoxy is difficult to apply gel coat over because polyester gel coat can’t adhere properly to epoxy. I however would disagree, from what I’ve heard as long as epoxy is properly cured and prepped it should be ok to gel coat over, however I may be wrong on that, I guess ill know in a few years if my gel coat starts cracking.

If it was me doing this project…I would use the same resin as was used to make the kayak. Creates less problems with repairs at a later date. more of a stiffness blend also. Homogeneous

Incompatible with epoxy, per manufacturer:

Incompatible with epoxy, per manufacturer:

From epoxy manufacturer SystemThree:

“Avoid using fiberglass mat with epoxy resins. The binder that holds the mat together is dissolved by the styrene in polyester resins. Epoxies don’t use styrene as a diluent, making it almost impossible to properly wet out the mat.”

And from your same source, West System:

If you read the last you will see that some types of chopped strand mat will not wet out well with epoxy. Stitched mat is better in this regard.

Epoxy will work just fine over polyester resins including gel coat. It is going the opposite way that one can run into problems. If you apply polyester resin or gel coat over epoxy it may not cure. The unreacted excess amines in the epoxy interfere with the cure of the polyester. I would not use polyester resin unless you know with certainty that your boat was made with polyester resin. Even then, I would use epoxy because it is much stronger.

If you know with certainty that your boat was made with vinylester resin you could of course use that for the repair. Vinylester resins have come a long way and I am told that some are now as strong as epoxy, which didn’t used to be the case years ago. But you can also use epoxy. I have repaired a number of canoes made with vinylester resins and have always used epoxy with no problems with cure or durability.

Vinylester resin has a limited shelf life whereas epoxy lasts years, although the hardener may redden a bit over time. So if you buy a quantity of vinylester resin and need to do a repair next year, it probably won’t be any good. The methylethylketone peroxidase catalyst that is used for polyester and vinylester resin is very bad if you should get any in your eyes. Lastly, the type of damage that Celia referred to earlier in this thread resulting from long-term water exposure to the resin occurs to a much greater extent with vinylester resins than with epoxy.

As for the issue of applying gel coat over well-cured epoxy, I have read conflicting stories. I have heard of people doing this with no problem. But I have read of a few horror stories of folks applying polyester gel coat over epoxy that had cured for years and wound up with a gooey disaster. But that is all second hand information and I have no way of knowing whether there was inadequate surface prep or an inadequate air barrier in these unfortunate instances. It might also depend on the particular epoxy. West System says that polyester gel coat can be used over their epoxy but surface prep is critical:

I was also talking about …down the road. I would never buy a boat of any sort that mixed resin types for repairs. Once you use Epoxy for repairing anything ALL subsequent repairs MUST also use Epoxy. Buying or selling a boat repaired this way would never be my choice.

When you see words like polyester resin, chopper gun, matt, kitty hair the alarm bells should be going off. Epoxy resin and fiberglass cloth or kevlar cloth and their various itierations are superior materials to work with. Repairs need to strong. Don’t compromise on materials.