Refinishing Fun – Like Rolling in Flypaper

It’s a slow day today and I decided to go refinish one of our older Souris River Quetico 18.5’s.  It’s a canoe that I have refinished once before and is in otherwise nice shape other than the outside looking in need of a new shine plus I needed to sand off graphite and epoxy that ran when I did a sloppy skid plate repair 2 years ago to meet an overnight time constraint.

Canoe Refinishing
Canoe Refinishing

So, just like every other refinishing job for a Souris River, it’s pretty straightforward.  Sand the parts that are oxidized and all the parts that are shiny using 80 grit sand paper and a palm sander.  I also removed a few clear epoxy runs from my hasty work a few years ago by leaning on the corner on the bump with the sander.  You have to keep the sander moving somewhat in order for the sanded epoxy dust to fall away and allow the grit to make contact with the hard, non-moving surface.  So, I do little circles on the runs being sure to used other parts of the sand paper on my palm sander.  Also note – do not use any other type of sander other than an orbital design.  If you use a belt sander you are going to end up in a whole world of hurt VERY quickly.  To sand a whole canoe takes about 30-45 minutes depending on your desired end result.    Just get it reasonably smooth, take a  “sander corner” pass over the length of the scratches and that’s it.  I then found my favorite brush that served me for 20 years as an XC Ski wax brush, and swept off the canoe.  I usually watch to see the way the wind is blowing and make sure I’m upwind so I don’t breath in the cloud of cured epoxy dust.

At this point, I put on some disposable gloves, grabbed a charcoal-colored foam roller, mixed up 6 pumps of resin and hardener, stirred it up, waited one minute, and dumped some of  it on the canoe.  Then I drove my roller through the fresh epoxy and I spread it around the canoe.  Pretty basic and quick.  I  rolled right along the bottom edge of the gunwale (which was upside down) and
continued up and down the canoe.  Applying resin to a dusty gray canoe makes it go to a pleasant brown with black stripes – or a  typical Souris River Le Tigre Kevlar.  This improves the look of the canoe about 1000% and I would eestimate that about 90% of all lay canoe paddlers don’t even realize the canoe has even been refinished.  Now, that may sound like a high number, but given my experience of the last 40 years of customers, I’ve decided that they are mostly incapable of noticing much at all.  They don’t notice crooked woodwork, canoe straps flapping in the wind behind a car with a canoe on the roof turned sideways on to the road below,  dangerous waters, or where to park their car based upon all the other  “seed” cars in the extremely obvious and easy areas to park in the lot.

kevlar canoe refinishing
This is a 2012 Le Tigre Kevlar Souris River in 2015.   The grey parts are dust from hitting the ground.  I got them out after the picture was taken.

What they DO notice is only on a brand new, shiny, unscratched canoe.  They go home and take a magnifying glass to the finish to look for the tiniest of imperfections (over every square inch) that don’t mean the most insignificant hill of beans to the operation of the canoe.  They also notice the top handle of a canoe paddle as they over-analyze its feel and try to picture using it on the high seas while standing in the store.   They also do notice when THEY are even slightly uncomfortable or getting rained on.  They do notice hunger, sometimes thirst, and when someone else is annoying them but not the other way around.  And that’s about it for 90% of the population of the world.

Kevlar Canoe Refinishing
And that’s a good thing.   The main reason being as I was refinishing this canoe (it’s going back into rentals), I had pretty much the whole thing coated with fresh epoxy when it slid off of my horses – in slow motion (Ooooooohhhhhh-Noooooooooooooo!)- and landed upright in the gravel, sawdust, leaves, pine needles, dog fur, old bits of dusty of kevlar, and dandelion fluff.  It was very special.   I said some bad words.  Actually, I repeated a choice four letter word loudly – and with relish. The whole event was like dropping freshly unrolled flypaper in sawdust.

So, upon the universal battle cry of refinishing gone wrong, plus the big booming noise a canoe makes when it hits the ground, Jackie came running out and helped me get it back on the horses whereupon I proceeded to ruin a t-shirt with an epoxy/dirt blend.   I then grabbed the roller, finished up the last few areas of that didn’t get covered pre-fall and I shot the pic’s of the finished canoe.  For the occasional bits of debris stuck to it, I’ll just knock those off after it cures.  I noticed that the digital pictures allowed me to see the dust that I missed when wiping off the canoe after the fall, so I went back and took care of that as well.  I couldn’t see it with the bespectacled or even naked eye.

So, my advice to canoe refinishers everywhere:  Don’t drop it in the gravel.

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Epoxy Resin vs. Vinylesters and Polyesters

Epoxy Resin vs. Vinylesters and Polyesters

Here’s a different way to look at epoxy resin vs. vinylester resin as was explained to me by an R & D chemist named Mike Daniels. Mike works for a huge Minnesota company and he does know his chemistry. Plus he has 25+ years of making all kinds of cool stuff and is an expert wood crafter. His stripper canoes and kayaks are rather spectacular. You just can’t help but trust a guy who is a seasoned chemist, canoe builder, and canoe paddler.

Vinylester resin forms a chain of molecules that kind of wrap themselves around a kevlar fiber. Now, I know that this is really perhaps oversimplified, but I am a simple man and definitely not a chemist. Using carabiners, the first photo on the left represents a strand of vinylester resin. Pretend that the paddle shaft is a kevlar fiber and the vinylester resin (carabiner chain) wraps around it in a fairly linear path. Those vinylester resin molecules follow each other in a chain formation and end up winding around the kevlar fibers as well. Sure, it’s strong, but it doesn’t make anywhere near as many contact binding points with the side of the very-nonporous, kevlar fibers as epoxy resin does.

Vinylester Resin around a kevlar fiber
(Actually a carabiner chain around a canoe paddle)

Vinylester Resin around a kevlar fiber
Vinylester Resin around a kevlar fiber

Epoxy resin around a kevlar fiber
(not nearly enough carabiners to do a great representation – but I think it works)

Epoxy Resin Attaching to Kevlar Fiber
Epoxy Resin Attaching to Kevlar Fiber

Crosslinking of Epoxy

The photo on the right represents the cross-linking that goes on with epoxy resin. The number of strands of molecules that link in from the sides of the kevlar fiber also link to each other and to other kevlar fibers fibers as well. The cross linking of molecules is virtually infinite and this results in a zillion contact points with each kevlar fiber in the canoe – and there are bazillions of those. Cross linking increases as the epoxy resin cures. In the photo above, I didn’t have nearly enough carabiners (needed a bazillion) to make a really great representation of epoxy’s molecular cross linking, but I think you can get the idea. The molecules of epoxy would actually link together to the fiber from all angles and directions. The number of links of epoxy molecules is to a kevlar fiber would be much harder to count than the number of links made by vinylester resin to a kevlar fiber.

The only way SR’s blend of epoxy resin cures is through heating it in an oven. The oven curing process and the need for high room temperatures to make the resin runny enough to squeegee thru four layers of cloth, are two of the main reasons you do not see epoxy resin used in all of the various Brand X kevlar canoes out there today. Vinylester resin is just easier to use at the factory level but nowhere near as strong as epoxy resin. The cross linking is just not there in vinylester resin and the kevlar fibers can pull out of the glue more easily when stressed via paddling into a big rock or over a log. A heat-cured, epoxy resin, Souris River canoe, because of the nearly infinite number of cross-linked epoxy molecules making contact with every fiber in the canoe (plus each other due to the catalytic reaction that goes on), a Souris River Canoe essentially becomes one big honkin’, continuous, plastic, molecule. Vinylester resin does not do this to the magnitude of epoxy resin and is therefore substantially weaker.The epoxy resin that Souris River Canoes uses is a very pure form of resin. It does not have the additives that are inside of the epoxy resins that us ordinary folks us can buy at the grocery store. Common epoxy has additives to allow mere mortals to use it at room temperature and actually have it cure while doing the cross-link thing. Even though the resin is still incredibly strong with additives that facilitate curing and allow us to apply it without heating it up, it is not as strong as the epoxy resin SR uses. Souris River’s epoxy formula is close to solid at room temperature and uses a combination of two different hardeners. It has to be heated up just to get it out of the container.

Thanks to Mike Daniels for ‘splaining epoxy cross linking to me and subsequently, to you.One final point – Heat-cured epoxy resin is used in the carbon fiber composite, V-22 Osprey and in Cirrus Aircraft. When it comes to flying, guess what? They don’t use vinylester resin in any important parts like the wings, fuselage, etc. That says a lot to me. If it doesn’t mean much to you, you haven’t been paying attention to all this typing.

Even More Information

Here is some other technical data that I gleaned off of epoxy resin websites by Maas and West Systems. (If you think this is just a sales pitch, heck, you’re sitting here looking at this web page on the internet – use Google and research it for yourself.) You may find it interesting regarding the differences between Epoxy Resin and Vinylester or Polyester Resins. In case you don’t already know it, Souris River Canoes are all made with a very high grade epoxy resin. Pretty much everybody else in the canoe world uses either vinylester resin and some the weaker polyester resin.  

In the marine industry, liquid plastics, namely epoxies, polyesters, and vinylesters are used to saturate (wet out) the fibers of wood, glass, kevlar amarid, or carbon to form a fiber reinforced plastic (FRP).  To create a quality part, adhesion to the fibers is the most important factor.  Not all resins keep their grip on fibers equally.

Epoxy resin is known in the marine industry for its incredible toughness and bonding strength.  Quality epoxy resins stick to other materials with 2,000-p.s.i. vs. only 500-p.s.i. for vinylester resins and even less for polyesters.  In areas that must be able to flex and strain WITH the fibers  without micro-fracturing, epoxy resins offer much greater capability. Cured epoxy tends to be very resistant to moisture absorption.  Epoxy resin will bond dissimilar or already-cured materials which makes repair work that is  very reliable and strong.  Epoxy actually bonds to all sorts of fibers very well and also offers excellent results in repair-ability when it is used to bond two different materials together. Initally, epoxy resin is much more difficult to work with and requires additional skill by the technicians who handle it.

Polyester resin is the cheapest resin available in the marine industry and offers the poorest adhesion, has the highest water absorption, highest shrinkage, and high VOC’s.  Polyester resin is only compatible with fiberglass fibers and is best suited to building things that are not weight sensitive.  It is also not tough and fractures easily. Polyesters tend to end up with micro-cracks and are tough to re-bond and suffer from osmotic blistering when untreated by an epoxy resin barrier to water.  This is really cheap stuff.Vinylester resins are stronger than polyester resins and cheaper than epoxy resins. Vinylester resins utilize a polyester resin type of cross-linking molecules in the bonding process.  Vinylester is a hybrid form of polyester resin which has been toughened with epoxy molecules within the main moleculer structure.  Vinyester resins offer better resistance to moisture absorption than polyester resins but it’s downside is in the use of liquid styrene to thin it out (not good to breath that stuff) and its sensitivity to atmospheric moisture and temperature.  Sometimes it won’t cure if the atmospheric conditions are not right.  It also has difficulty in bonding dissimilar and already-cured materials.  It is not unusual for repair patches on vinylester resin canoes to delaminate or peel off.   As vinylester resin ages, it becomes a different resin (due to it’s continual curing as it ages) so new vinylester resin sometimes resists bonding to your older canoe, or will bond and then later peel off at a bad time. It is also known that vinylester resins bond very well to fiberglass, but offer a poor bond to kevlar and carbon fibers due to the nature of those two more exotic fibers.  Due to the touchy nature of vinylester resin, careful surface preparation is necessary if reasonable adhesion is desired for any repair work.