EnviroYak: Kayak Repair and Construction with Gel Coat and Epoxy

I used to do a fair amount of repair each year on my boats – didn’t often take photos, but a few below. I've grouped these by "Gel Coat" and "Epoxy", which are used for somewhat different purposes. Gel Coat is really a surface treatment, it forms (and is used to repair) the hard, rigid outer shell of the kayak. Epoxy is more a "glue", which can be used to make wooden boats and also used to repair holes and deeper damage to fiberglass kayaks, typically in combination with some patches of fiberglass cloth. Rule of thumb for me is if you have a real hole/leak or damage that goes down into and through the fiberglass, you need Epoxy - use Epoxy Resin on the inside of the boat for the initial repair to make the boat watertight again, then finish exposed areas on the outside of the hull with gel coat. If the damage is only in the outer Gel Coat, but the underlying fiberglass is largely undamaged, then Gel Coat is all you need for the repair.

Gel Coat:

If you remember nothing else, remember “Get the FINISH Gel Coat” kind, not the laminating gel coat. See photo of Gel Coat can below. This type air-cures so is the one you want for repair – doesn’t require a barrier film over it, which is a pain. Gel coat is typically white for hull repair - forms the outer coat (shell) that protects the underlying fiberglass from abrasion damage and UV sun exposure. Like automotive "bondo" it is made to harden by adding several drops of a clear liquid catalyst (methylethylketone MEK), that has a recognizable smell. It's easy to work with, but I always use goggles when I mix it because the MEK can damage the eyes if a drop gets in. I used to fill gouges and deep scratches in the gel coat on my kayak hulls maybe once a year with new dabs of Gel Coat. But even a small job requires some work and that you return the next day to sand it down. So, I eventually got tired of that and only fixed major Gel Coat gouges or areas of impact that exposed the underlying fiberglass, as shown in the images of my repair job below - you can see the underlying fiberglass weave. Deeper areas of damage in the Gel Coat that expose the fiberglass layer underneath are “functional” (not cosmetic) and require Gel Coat repair because exposed fiberglass can absorb water or shred the fibers more over time. (Not immediately, you can still paddle the boat unless it's leaking but covering areas of exposed fiberglass with new gel coat soon is wise). Shallow surface Gel Coat scratches or spider cracking aren't a problem and IMHO need not be repaired. Photos below show repair needed due to a big whack that occurred while RI rock-gardening. For that repair, I was using a Dremel tool and 80-grit sandpaper to remove all Gel Coat at the damaged area down to the fiberglass. I applied a few coats of Gel Coat (perhaps 2 coats to build it up, the second painted on after the first was tacky) followed by wet sanding after it was fully cured/dry with 600 grit sandpaper. The better you prepare the damaged area by sanding away loose/cracked gel coat, the better the repair area will do - repair will be imperceptible when it’s done. But more shallow, simply cosmetic Gel Coat repairs are often too thin to hold up well - the new gel coat will just crack again. So, unless it’s a major repair, I’ve learned to leave cosmetic scratches and spider cracking alone. The hull’s gel coat is meant to be a sacrificial barrier anyway, to protect the underlying fiberglass – once it’s really bad you repair it. I have a friend who had his entire 20-year-old kayak hull re-sprayed professionally with new Gel Coat for $600 in Norwalk CT - worth it to him since he loved the boat. Or, once your hull is really worn, you can add a keel-strip with fiberglass tape, polyester resin and gel coat (a semi-big job which I did once to a kayak I later sold, no photos).

Rock-gardening casualty

This is the stuff - FINISH Gel Coat

Added patches of fiberglass cloth where heals damaging hull and at leak area - I should have used Epoxy for better strength instead but didn't have any handy

Dremel down to expose fiberglass

[Technical Note: Gelcoat is a special type of polyester resin mixed with coloring agents and UV inhibitors that protect the boat’s underlying fiberglass. When a boat is manufactured, “laminating” gel coat is sprayed into the boat mold. This type of gelcoat will not fully dry – it will stay tacky. Fiberglass cloth and resin (polyester, vinylester, or epoxy resin) are then added on top of the gelcoat such that the two materials (uncured “tacky” gelcoat resin and fiberglass resin) bond chemically, making the protective coating very strong. By comparison, subsequent repairs made by kayak owners with air-curing gelcoat must bond physically, not chemically, so they require that the repair area be roughly sanded to make a better bond. That’s why gelcoat repairs are never quite as strong as the original chemical “gelcoat-to-fiberglass resin” bond.]

Epoxy:

I used 2-part MAS Epoxy (a few gallons) to make the CLC North Bay kayak in 1999, photos below. A testament to the fact that anyone can make a stitch-and-glue boat! I did a messy, novice job - but the thing was water tight. Finished product looked great on the outside with a lot of sanding, a few coats of varnish and some wood inlay for decoration. That's one nice thing about wood boats, each spring you can lightly sand and add a coat of varnish making the hull like new.

In addition to its use in wood kayaks, more significant fiberglass kayak repairs can also be made with Epoxy (MAS or West System), especially on the interior of the boat. After Epoxy dries you need to cover sun-exposed areas with paint, varnish or gel coat since epoxy has no UV protection in it. (Yes Gel Coat can be applied over Epoxy - see video here.) Epoxy seems more "tacky" feeling to me, less hard/brittle than Gel Coat. I've also heard it is more tenacious than gel coat, able to bond to things with less sanding and acts more like glue. That's why it should be used for holes, and more major repairs. Also, unlike Gel Coat (a polyester resin), which just requires a few drops of the catalyst, Epoxy is composed of a two-part "resin" and "hardener" that are mixed in more equal proportions. Lastly, epoxy doesn't smell as strongly as Gel Coat (in fact I can't smell it at all most times). Some say wet epoxy is less toxic compared to Gel Coat (which is made from polyester resin) if it gets on your hands. I'm not sure about that - I always were gloves when dealing with either substance. When sanding a big surface of freshly cured epoxy (as when making a wooden boat) it's also wise to use a respirator and gloves (as in photo below). Fully cured epoxy can be sanded with just a dust mask. For small repair projects, such as fixing an interior leak below the seat or repairing a paddle, I've used the easy-to-use West System 101 kits of epoxy (photo below) - the resin and hardener come in little envelopes with some silica dust to thicken and a mixing stick. I’ve also used epoxy sticks (photo below) for "field" repair of a holed kayak that I dropped while on vacation. An epoxy stick has the consistency of clay – you rip off a piece and knead it to combine the two-parts and it hardens in place. Later you can sand off the outer portion of the repair and cover with Gel Coat.