Kevlar Canoes : Souris River vs. Brand X – Epoxy does it best

It’s been a while since I’ve laid out a small dissertation about the differences in kevlar canoes.  As years go by and the markets change, people who know the differences are a fading group.  I will change all that right here.  All kevlar canoes are NOT the same despite looking similar to one another.

Souris River Canoes hulls are all made with kevlar cloth, a few other layers of cloths including polyesters and fiber glass and most importantly: epoxy resin.    All Brand X kevlar canoes are made with kevlar cloth, a few other layers of different cloths and important for you not to miss:  vinylester resin.

The resin used to hold the cloth in the shape of a canoe is first and foremost, the most important part of the canoe.  A canoe could be built out of newspapers or old sweatshirts but the only way that is possible it to use resin.  The type of resin used, along with literally the “cut of the cloth”  defines the canoe’s overall strength and durability.

I’m going to cut to the chase.  Epoxy resin is much tougher than vinylester resin.   Epoxy resin used in a Souris River Canoe is a heat-cured epoxy.  After the canoe has been laid out in a female mold with wet epoxy resin, they wheel it into a big oven and bake it for several hours.  Baking epoxy to cure it makes it runny and it seeps into the multiple fibrous tendrils that make up every kevlar fiber.  When it cures (dries – although technically not the same as curing since drying means a solvent evaporates and curing is a chemical reaction that leads to a hardened, non-liquid, state.) it becomes inert “plastic” but not before it bonds all those fibers together to make them more of a single piece of material with kevlar reinforcements running throughout.

Brand X uses vinylester resin which is a resin that costs far less than epoxy.   It too, makes a plastic with kevlar reinforcements running throughout when applied to a kevlar cloth.  However, the process by which it cures, while still a chemical reaction, is different than epoxy.  Vinylester resin used in Brand X kevlar canoes is cured at room temperature or about 74 degrees F.  That means, they wet out the kevlar in a female mold,  and once saturated with the excess resin scraped out with squeegees, (just like Souris River) the canoes are allowed to cure (dry) at room temperature overnight.  The next day, they beat the mold off of the hull with a rubber mallet, install the gunwales, seats, thwarts and yoke and out the door it goes.

At this very point, the two canoe brands have severely parted ways.  Inherent with epoxy resin, when it is done curing, it is done curing.  It does not age for lack of a better term.   What that means is the Souris River, after 10 years of paddling, when you go to do a repair on the canoe (yes, they’re tough, but nothing is as tough or heavy as aluminum, eh?   You may need to fix something once in a while), that old epoxy resin is still the same as it was the day it came out of the over 10 years ago.    So, when you take out some new epoxy resin to do a repair, you are bonding apples to apples – the same stuff.  Doesn’t make sense without the following comparison in the next two paragraphs.

Inherent with Brand X kevlar canoes, the room-temp-cured resin first, did not soak all through those kevlar fibers in each strand bundle that is woven together to make a cloth.  When curing at room temperature, that vinylester  resin doesn’t have a chance to soak in because it begins to cure and thickens before the soaking begins.  That means it ends up encapsulating the fiber bundles.  Well, that means, too, that less resin is needed and it makes the canoe lighter.  It also results in the canoe not being as tough.  If you rip the resin coat off the fiber bundle, water can enter into those fibers through capillary action.  Once that happens, an entire region in a canoe can delaminate from other fibers in the cloth or the foam core floor they use in Brand X to keep the floor of the canoe from flopping around.  It’s a diamond shaped looking thing with ribs running up the sides.  The foam ribs also support the sides of Brand X canoes because they are not as tough with the lesser resin saturation inherent with vinylester resin canoes.

But, it doesn’t end there.  Vinylester resin that has been air-cured continues to cure into perpetuity.  It’s really not done curing, it’s just not sticky any more.  What this means is that this resin gets more and more brittle with each day.  The resin is susceptible to UV radiation and that ages it.  Now, to be fair, epoxy resin is affected by UV as well but in a different way.  It does not become brittle.  It sloughs off a little at a time.  But, unlike vinylester resin, you can reapply epoxy with great results and a paint roller.  Not only is vinylester more brittle in the long run, it is no longer the same vinylester resin it was when the canoe was first built.  This means than when you put your foot through the side of a brittle vinylester resin canoe and need to repair that, the company Brand X will tell you to go to the local Fleet Farm and buy some polyester resin and the MEK  (methyl ethyl ketone) hardener or organic peroxide which might be the same stuff.  I don’t know, I’m not a chemist but over the years, I have spoken with several regarding the advantages and strength of epoxy compared to vinylester and those advantages are very significant.

At the molecular level, vinylester resin links to itself with a relative few bonds when compared to epoxy.  Less link ups means less strehgth.   Epoxy resin is noted for having  many, many cross-linked bonds to that which it is being glued together.  For that reason epoxy provides a substantially stronger bond of materials and is also noted for it’s ability to bond non-related materials, such as a copper penny to a piece of wood.  Vinylester resin may bond those two together, but then it will let go at the most inopportune of times.   The cross linking of molecules in epoxy also give it the ability to flex repeatedly without falling apart or cracking.  The whole focus about Souris River Canoes is their ability to flex under duress to minimize damage caused by driving it up on a rock.  Brand X, with their foam core bottom can be damaged significant when one drive them over a rock 4 inches below the surface and invisible.    Souris Rivers just slide over it with no exposed kevlar fibers resulting from the impact.  As you recall above, exposed kevlar fiber bundles in vinylester resin are like tiny hollow tubes that can suck up water and cause delamination at that area.  It doesn’t always happen, but when it does, you end up with a soft spot that needs your attention or it can continue to spread.

Putting a patch on an older Brand X canoe using their recommended method of applying cheap polyester resin to a piece of fiberglass or kevlar  patch and sticking it onto the canoe will,  more often than not, result in that patch letting go in six months to a year.  But it usually does not all let go.  Nosiree – only half lets go and the rest stays stuck to the canoe so you have like an “air brake on the wing of a 747”.  Or, you could consider it a water scoop since they usually let go against the direction of travel.  In my opinion, polyester resin probably has it’s place somewhere out there in making fiberglass bathtubs with a thick layer of gel coat, but it’s a worthless product for working on canoes.    It is also hard to work with as well.  It’ll say on the container of resin to add 2-3 drops of hardener.  Well, which one is it?  2 drops or 3 drops?  Depending on the ambient temp and humidity levels, 3 drops could turn the resin in your pot into a smoking, toxic mess that smells like burning styrofoam beer coolers.  (been there, done that – an wow, does it get hot!  Epoxy will do the same if you put too much in a con)

Epoxy on the other hand is more precise in it’s requirements for hardener and those different hardeners can affect cure time.  West System 205 hardener can set up in 9-12 minutes, but their 207 special coatings hardener can go to 6 hours before hardening the resin mix depending on temps.  West System epoxy mixed with either hardener achieves full strength over 7 days.  It’s will be dry to the touch and usable before that, but that is when final cure is complete.  Polyesters continue to cure (and change as a result)  forever.    Now, I mention West here because that is what I recommend for repair work mainly because I know it well and have used if for 20 years with excellent success about 99% of the time.  There are other marine epoxies out there that are quite good as well, but I just never had a reason for changing.  They are all expensive.  Note: Souris River does not use West System in the building of their canoes.  They use a purer form of resin with two hardeners injected into it at two different temps.  Then it is applied by hand in a 94 degree F room and then wheeled into a large oven to be heat-cured.  West System has additives to make it cure for repairs without the baking-part required.  If I had to be heating up resin and baking it, that would be a pain for me and everybody else who doesn’t have a canoe-sized oven.

So those are differences in Souris River Canoes vs. all the other canoes out there.   Sure, there might be a garage-outfit somewhere using West to make a canoe a year, but in the professionally, hand-crafted, production realm of canoe building, SR is the only epoxy kevlar canoe builder of which I’m aware.

More on Hull Shapes and Design in future posts.


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