How to I go about repairing so pretty serious fiberglass spidercracking

I have made it a hobby to bring old sea kayaks back from the dead so i have some advice for you. I grew up in a fiberglass boat building shop so I have seen my fair share of glass work. There are already some good points made here by other paddlers but I will pile on my own anyways. 1) Don’t cut away any part of your boat. Leave the original materials to help shape the repair. 2) Do all of your repairing from the inside. That way you don’t need to fair out a wacky patch on the outside. For deck repairs hang your boat up-side-down from the garage rafters at about your shoulder height so you can stand with your respirator clad head inside the cockpit to work. 3) Gelcoat cracking can also be simply age, it will shrink at a different rate than the substructure so it may just be showing its age. 4) The whole story of the condition of the woven laminate can be seen from the inside, if you see white spider cracks then this is where the impact happened or the stress had occurred. 5) Use polyester or vinyl-ester resin for the repair. Its cheaper, easier to sand and work with and much more commonly found. Epoxy is for-sure a better material but not important to a repair to a boat that is mostly made from Polyester 6) Try to keep the repair as minimal as possible so you don’t add too much weight to the boat. 7) The inside patch can be super simple, sand the area really well, wipe down with acetone. One layer of 1oz mat to help take the shape of the surface, 2-3 layers of 9oz boat cloth. Add your resin judiciously working to use the lease amount possible and still wet out the materials. Tip, I will sometimes make the patch on a scrap of cardboard so can carefully get the materials wetted out with the lease amount of resin. I then transfer this patch to the boat and tap it down with a wet chip brush. It can look a lot tidier too. 8) If you want the boat to look pretty from the outside it is possible to fix the gelcoat cracking or at least fill it and smooth it. I usually don’t bother and instead just lightly wet sand with 400 grit and buff the surface to a shine. These boat are not show pieces, they are tools meant to do a job. Take it out on the water and put some more scratches on it. I’ve had boats that were literally split down the middle and left for dead that I brought back and did 2 week expeditions in. Fiberglass boats are amazing, I make it my mission to keep them out of the landfill.

Paddle-on Lads


From your experience how do you determine if the boat is epoxy or polyester, already purchased epoxy resin and was worried maybe that was a bad choice if the boat is polyester. However I assumed old WS boats were epoxy since the repair manual I found mentioned epoxy

Very few {if any} production kayaks especially older ones were ever done with epoxy. The combination of time restraints and curing and initial expense.

The Poly esters or Vinyl esters work well when placing layers into partially cured Gel Coat in a mold and working and cure time allows a quicker build from the days before .

I don’t think Wilderness systems ever used Epoxy. {I could be wrong, but doubt it}

Boats with an epoxy build are more in the vein for racing. You will see the use of clear coat rather than gel coat.

Epoxy is more expensive in a build. To be absolutely sure of any particular build, contact the maker.

Smell, i know this is a strange answer but that is a clear way to tell. Polyester vs Epoxy has a certain smell. Hard to describe. Lightly sand surface and you will smell it. I feel I can say this with some confidence that your boat is a Polyester boat. This is because if its age. In that era it was mostly Polyester for a lot of reasons. It was cheap and easy to get and most builders were very familiar with the material. If you already own the epoxy then by all means use it. Prepare the surface the same way and use the same laminate. Epoxy bonds OK to cured aged polyester laminate so don’t worry.

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You know…all this talk about how bad this kayak is and all the cracks. It would help if you posted a few pictures. {or did I miss them?}

We all have different ideas as to what is REALLY bad. It might change some suggestions. Remember the Gel stiffens the hull so the laminate might be just fine.

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As I said before, epoxy will bind just fine to composite hulls constructed with either polyester or vinylester resins. Polyester resins are so very distinctly inferior to either epoxy or vinylester in both strength and water resistance that I would never consider using it for any type of boat repair in which strength is required. I would only consider using a polyester resin gel coat where strength is not an issue. There are only two virtues of polyester. It is cheap and easy to work with. But those advantages are completely negated if your repair fails some time later.

Vinylester resins have some very distinct advantages for boat manufacturers and that is why they are now widely used for construction of complete hulls. First, it is cheaper and that is a big advantage when you are using a lot of resin. Second, it is less viscous than epoxy. That means that mulitple layers of fabric laid into a mold can be more easily and uniformly wet out at once. That is particularly important when using a vacuum bag technique and even more important when using a resin infusion technique. The cure rate of vinylester resin can also be accelerated by adjusting the amount of catalyst added to the resin so quicker cure times can be achieved. The limited shelf life of vinylester resins is not a limitation to the manufacturer who is using up the resin continuously.

The only one of these advantages that applies to a consumer doing home repairs would be the lower cost. Unfortunately, that is usually completely offset by the fact that the resin must be purchased in fixed quantities that are usually more than the repair requires and by the time the next repair comes along the resin is no good. Epoxy resin and hardener must also be purchased in fixed quantities but has an indefinite shelf life and epoxy can be used to repair many different items besides boats so there is no wastage.

Epoxy does tend to be more viscous and can be a little harder to work with initially but that issue is quickly overcome. Vinylester resins do have significant toxicity. As I said earlier, the MEK peroxidase catalyst must be handled with care. But there are also volatile toxins given off by the reaction of the resin and catalyst, primarily styrene vapor. This can be an issue if you are working on the interior of a kayak with your head up inside of it.

As I said earlier, in your case either epoxy or a good vinylester resin should work. But if you already have epoxy that is clearly what I would use. There is a lot of misinformation floating around about epoxy. Here is a short article from West System that discussed and debunks some of them:

A good and free on-line educational resource if you have not done lamination with epoxy before is “The Epoxy Book” by System Three (a well-known epoxy manufacturer). Although specific System Three resins are discussed in the book, most of the information applies to the use of any type of epoxy. But be aware the the mix ratios of resin to hardener are different for different manufacturers and different epoxy types. So be sure to use the ratio prescribed by the manufacturer of the epoxy you have if it differs from what is given in the book:

The book is fairly long so pick and choose the parts that seem pertinent. If you haven’t done much work with epoxy resins and fabrics I guarantee that the time spent reading will be repaid several times over by avoiding mistakes and frustration.

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Sorry I actually have my kayak located far from me right now and I won’t be going to have it for another week, as soon as I get to it ill sand off the gel coat and take some photos

Take pictures before you sand.

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Not nearly as bad as I thought, I’m think it may be best to put another patch inside and lay epoxy in the outside before gel coating.

The picture in inside is after sanding, I forgot to take a picture from outside after sanding but will as soon as I can. Right where the crack is the composite is rough and has some loose fibers compared to the smooth surrounding area

I would mark an oval around the visible crack on the interior of the hull that extends 2" from the crack in all directions. Apply a patch of either 6 ounce/square yard plain weave fiberglass (S 'glass preferred) or 5 ounce/square yard plain weave aramid (e.g. Kevlar). Let the epoxy cure and then press on the hull exterior over the patch to see if the repaired area now seems to match the stiffness of the rest of the deck. If it still seems to have a bit too much give, apply a second interior patch that is concentric with the first but cut at a 45 degree bias to the first, the second patch extending 1" from the edges of the crack in all directions.

You really don’t want the repaired area to be any stiffer than the undamaged deck otherwise you will have a compliance mismatch that sets up a stress riser at the edge of your repair which will predispose to cracks forming along that stress riser. Making the second patch (if needed) 1" less in size than the first will also tend to diffuse the stress riser that would otherwise exist.

Remove any loose fragments of gel coat that have delaminated from the structural fabric and bevel the gel coat at the edges before repairing the exterior gel coat. I would ignore much of the spider cracking if the gel coat otherwise appears intact and well-attached.

I have a question, I know you said as #1 not to remove the old material because the shape is needed, but could I just use the old material to retain the shape? I was considering using a dremel to cut a hole out of the old material and then cover the piece with cling wrap. I would like to then use it as a guide for the shape laying in new material. I am just worried if I leave the old material in that the fiberglass cracks may grow over time from flexing and crack any new gel coat I apply. Is there anything I could do to retain shape while replacing old material?

In order to retain the shape, your best bet is to apply a layer or two of fiberglass and epoxy on the inside first. Then, you can remove the gelcoat and if need be, the original fiberglass by sanding it.

I would NOT use a Dremel, as it’s too aggressive and too difficult to control. It’s also really tough to get even results on a larger area with a tiny sanding drum. This is a classic case where using the wrong power tool just makes it easier to do more damage, faster.

Sand it by hand using a rubber block, like those used for auto body work. That provides excellent control and the ability to easily change grits as necessary. You’re not removing a lot of material, so it doesn’t take long to do it this way and you’re far less likely to screw it up. Remove the damaged gelcoat and any damaged fiberglass. Feather the edges well before applying any new fiberglass and/or gelcoat.

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If fiberglass has delaminated from the resin matrix I would remove the portion that has delaminated. As long as you can impregnate cracks with fresh resin and cover the damaged area with new fiberglass, the existing cracks will not grow.

As anystrom said, if the interior is accessible apply the initial patch there.

Unless you have much more extensive damage than your photos show, I see absolutely no reason to completely cut out a section of the hull (or deck).

It is a little bit worse than in the photos as the cracks did not show up on camera. For a spot the size of my hand the fiberglass in noticeably weak but if nobody else recommends it I guess I should not remove it, so I guess i will just patch the inside and add some resin on the outside. before adding gelcoat.

If you have to debride delaminated fiberglass from the exterior of the boat, I would use an exterior patch to replace it, not just resin, before applying gel coat.

For through and through cracks I usually prefer applying patches on both sides although if several patches are required the majority can be applied on the inside so that you don’t have an area on the exterior that stands proud of the rest of the boat. If the cracks can be precisely approximated, or there is no displacement of the cracked edges, and no 'glass has delaminated, you can probably get away with just patching the interior and filling in the cracks on the exterior with resin.

Again, you don’t want the repaired area to be stronger and stiffer than the adjacent undamaged hull.

I only use interior patches to help maintain the shape of the hull and add a bit of strength. I never use more than two layers of 6oz. glass. If I remove any of the original glass, I replace it on the outside, where it came from, and build it to the same thickness as the original glass. That way the gelcoat will be the same thickness as the original, too. If you don’t have to remove any glass, you obviously don’t need to replace it.