epoxy canvas filler

dannyS

Curious about Wooden Canoes
I'm currently working on a 14' huron canoe. A local boat builder has suggested west system epoxy with 410 microlight filler. he's had great results in the past but I was wondering if anyone else has tried it? I can't find much with the search option.

what are your opinions on epoxy as a filler? apparently the microlight is quite flexible.
 
To start with, 410 filler compounds are made for easily fairing hulls that don't hit anything or get beached. It is about as soft as plaster once hardened, so it's going to get chewed up pretty easily on a canoe. No, it is not very flexible when mixed with typical epoxy resin. You might be able to make it more flexible by mixing it with G-Flex or similarly more flexible epoxy resins, but it is still going to abrade awfully easily. Then there is the color thing. Gougeon Brothers cautions users that 410 should only be used under light-colored paint to prevent excessive heat from damaging it. Put your typical dark green paint on the boat, stick it on top of your car on a hot day and wait for it to start cracking. Cotton canvas loves epoxy. It would seem to me that it could be a serious problem trying to keep it from absorbing too much, or from sucking the resin out of your filler mixture, leaving it weakened. If you're bound and determined to fill with epoxy, I think I'd try 407 instead of 410 as the filler. It is tougher (though still nowhere near as tough as traditional filler), still sands well and doesn't have the vulnerability to heat that 410 will have.
 
I went around and around on this myself not too long ago. I have a lot of experience using epoxy - and to wake up the next morning with it cured and hard and ready for final sanding then painting in a couple days was really an attractive concept. After investigating lagging compound, Eko-fill, Zinnser water-tite concrete sealer, Sherwin Williams Pro-block exterior latex primer, etc etc, I got a gallon of Rollin Thurlows mix (alkyd silica) and within a couple hours it was a done deal.

I have ground to a stop several times over barely submerged boulders (damn sun in my eyes), I have dragged the boat loaded over beaver dams, it has spent the summer outside inverted on saw horses when not on the truck or in the water, and at the end of the season, another coat of gray paint will have it all looking fine. The canvas has come through unscathed.
I'm by no means a traditionalist, and I love to tip sacred cows, but I'm now pretty convinced that the traditional filler really is the best stuff for wood-canvas canoes.

However, I haven't yet tried 3M 5200...it comes in brown, white, and I think black. It could be blended for any shade in between and applied directly to the canvas with a squeege. It takes a while to set up so there would be time to really work it smooth, but within about a week it would produce a nice tough, waterproof coating

Oh, and I heard somewhere that Dupli-color Bed Armour - a spray-on/brush-on truck bed liner - makes a nice durable non-skid finish for the inside of a canoe...
 
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Epoxy

A while ago I helped fill canvas with epoxy thickened with talc to allow it to be sanded. The thickened epoxy did not penetrate the canvas, so no sticking to hull issues. The canoe worked fine and was left outside for several years with no problems. Drawbacks were all the mixing of batches, getting it smooth, added cost. I doubt it is much better than traditional filler, but it seemed to be a durable, and viable way to fill canvas.
 
Well I thought, Id let everyone know that i went ahead with Epoxy as a filler. I used west system with 410. mixed to a honey like consistency.
the canvas absorbed the filler and epoxy very nicley.canvas did not bond to the hull at all and the result is very flexibe. after filling i painted with interlus pre-kote and sanded, followed by interlux brightside paint. very easy to apply and ready for paint the next day.

Give it a try if your looking to experiment!

Danny
 
Interesting but I remain skeptical.
If the boat can survive a late July/August run down the Penobscott/Allagash without opening up like a sardine can...that would convince me.
Our Traveler with Rollins filler gets abused and though it has some scars all it ever needs is a bit of touch up from time to time and a fresh coat of shellac in the spring.
I'm lined up with LJ on this until you can include a few trip reports.
Pond and lake paddles don't count...
Load your boat to the gills and paddle with a careless (or clueless) partner for maximum effect.:D
 
oh i realize that... it's still a work in progress I'll keep you posted. i give my boats a hell of a beating. over the years. i'm curious to see how it holds up.

just wanted to say that application was very easy!
 
Ease of application was never in question. Technically speaking, WEST epoxy is generally not ready to paint the next day (or sand much if you care about your health). It takes about a week for the epoxy to reach a final cured state, which makes the sanding dust a lot less toxic. The test will be how it holds up (softness of 410 mixes being a very serious issue) and whether or not you can have the canoe on top of your car in the summer sun and keep the surface below 140 degrees or so (about where the epoxy starts to soften and break down from the heat). It would be a very good idea to paint that canoe white.
 
... and whether or not you can have the canoe on top of your car in the summer sun and keep the surface below 140 degrees or so (about where the epoxy starts to soften and break down from the heat). It would be a very good idea to paint that canoe white.

In light of this, it is interesting to note how many advocate the mixing of graphite powder in with the epoxy to form a hard, slick, abrasion resistant surface for the bottom of canoes (mostly wood strip). I believe there is a builder in Minnesota that uses epoxy/graphite for the bottom of his WC canoes. I've used it on a wood strip kayak I built, but I'm not really certain that it does, in fact, make the surface any harder or more durable. I agree with Todd that the 410, though easy to fair, is going to be much softer, but it will be easy to touch up with more glazed into the deep scratches prior to repaints.

I have a strip West System epoxy guide-boat painted flat black on the outside. It has spent its 13 years inverted in the sun, on the rack, or on the truck parked in an asphalt parking lot. I haven't noticed any significant consequence, but it certainly did get hot to the touch. After a few sand down and repaints over the years, I noticed a fine split in the 4oz e-glass right along the bilge which prompted me remove all the glass on the outside using a heat gun and putty knife. It came off with a bit of a fight but with plenty of heat the epoxy released the glass, then I scraped and sanded the residual epoxy off the cedar. I re-glassed with 6oz cloth and System Three epoxy, with several additional coats over the filled weave. It will be interesting to see if it will withstand the same abuse as the West System/4oz did.

Of note, I really liked the 2:1 system three - I'd used only West for years but now I'm a convert.
 
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hard, slick, abrasion resistant surface for the bottom of canoes

I did a bunch of rather crude tests on epoxy/graphite mixes, comparing them to plain resin a few years ago and as far as I could tell, they were neither harder or more abrasion resistant than plain resin. In fact, they were noticeably softer and less abrasion resistant. The advantage they had was in slickness. For example, your canoe might slide off of a river rock easier with the graphite coating, but the material itself tended to scratch deeper than plain resin did and left more stuff on the rock. The test method used was admittedly not very scientific, but was an attempt to simulate real world activities. Sections of cedar planks were covered with the two materials, weighted, and literally pulled across a big brownstone rock that my wife dragged home from Lake Superior. Using the same weight and about the same speed on both planks, the result was considerably more black stuff (graphite mix) left on the rock than white stuff (plain epoxy) though it took a bit less force to move the graphite plank. This was using about 10% graphite in the mix, which is what Gougeon Brothers claim is enough to form a good UV barrier for the resin (which is a plus for graphite mixes as UV is always a concern when working with epoxy). Higher amounts of graphite in the mix tended to make it even softer, so there was no advantage to them. The addition of some cabosil (think powdered glass) to the epoxy and graphite would harden the mix, though at some point you're going to change the viscosity enough that it might get difficult to spread it evenly. Using the hammer test on hardened chunks (put them on the bench and hit them with a hammer) there was a difference in the brittleness between plain resin and graphite mixes and for what it's worth, the more graphite added, the less brittle the sample was and the better it would survive.

My personal conclusions were that in most cases, I don't think it's worth it as a coating, since most of us don't tend to pound our wooden canoes recklessly down shallow rocky streams. Cosmetically, since epoxy doesn't self-level like paint (even when rolled and tipped) if a graphite mix is just applied and left that way, it's pretty ugly. On the other hand, when sanded smooth and left with a satin finish from fine-grit wet-sanding, it is a pretty darned elegant charcoal gray. Sanding it is a pretty messy job though with all that black dust. If I was going to do a graphite bottom, I would also do it mid-summer and "bake" it. If you apply the resin and then roll it out in the sun, or stick it under a makeshift dark-colored tarp-tent on a hot day so that the temperature it is curing at is substantially higher than normal, it will raise the heat damage threshold of the finished product.

I didn't bother to do a similar test with 407 or 410 fillers. I've used and sanded enough of them repairing and rebuilding boats to be pretty sure that the same drag test would have worn down quickly to bare wood and the hammer test would have powdered the impact spot. The aluminum flake "Barrier Coat Additive" seemed to make the toughest sample in terms of abrasion. It wore down even less than the plain resin and was pretty tough stuff without seeming brittle. Aluminum canoes are known to "stick" on rocks, but I don't believe there was enough present to worry about that. It's also a bit harder when you go to sand it smooth, but not too bad. I have, on occasion, seen paint problems with it though. When you sand an aluminum/epoxy layer smooth, you are exposing tiny bits of raw aluminum. These start to oxidize immediately as all aluminum does. Anybody who has ever tried giving a Grumman a home-paint job is probably aware that paint doesn't stick very well to aluminum unless you do a lot of prep first with etching and/or special primers. I have seen paint jobs on epoxy/aluminum flake mixes where the whole surface developed very tiny (pin-point-sized) fisheyes (holes in the paint layer) where the paint wouldn't take on the flakes. In one case on a two color boat, one color did this and the other color of the same brand of paint went on fine. The aluminum powder does make for a tough surface, and also a more water-resistant epoxy layer. Epoxy is the best stuff we have available at resisting water penetration long-term, but it's still not perfect. When you fill it with aluminum flakes, the water would actually need to zig-zag around the flakes to get through - thus the reason it is used for moisture barrier coating. On a canoe as a canvas filler, it might be worth trying if you have a primer that would handle the potential paint problem. Left raw, it's a pretty ugly, battleship gray color.
 
... When you fill it with aluminum flakes, the water would actually need to zig-zag around the flakes to get through - thus the reason it is used for moisture barrier coating. On a canoe as a canvas filler, it might be worth trying if you have a primer that would handle the potential paint problem...

Maybe that yellow-green zinc chromate primer used on aircraft would work albeit perhaps pricey.
Still seems a spendy high-tech way around plain ol' oil based silica canvas filler and porch paint.

That said, I'm a bit disappointed in the comma cracks and fissures developing in the bottom of my canoe filled less than a year ago with Rollin's mix. Despite mixing it to even consistency and compulsive mixing while applying, it went on weird, rapidly becoming clay-like and dry even to rub in beyond a glaze coat over the top of the weave. I did use up the whole gallon on the canoe and just barely filled the weave, so it all went somewhere. It dried over about seven weeks prior to painting with oil based paint. It then lived outside for the season and saw it's share of submerged rocks and was dragged over a handful of beaver dams. I pulled it into the shop a week ago to repaint the outside and discovered a large patch of comma shaped, raised ridges and fissures which I sanded somewhat flat before applying another few coats of paint.

I don't know what to make of this...except that I have created some real thread drift...
 
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You could always prime the aluminum mix with a coat of plain resin, which would bridge the tiny flake holes, but it adds another round of sanding. Actually, the manufacturers also suggest this for any microballoon-based filler as well, if you want a decent paint job. Once the microballon surface is sanded smooth, some of the balloons at the surface get cut open during the process. This will actually leave the surface covered with very tiny, air-filled craters. Paint will usually bridge most of the gaps, but won't flow down into them and fill them. Any rise in temperature while the paint is drying may be enough to cause little bubbles in the finish, as the air in those craters expands and pops the paint film. Resin is gooey enough that a resin top-coat won't usually do that.

Traditional filler does sometimes seem to be a crap-shoot in terms of lifespan and problems, but I'm not sure that epoxy filler is ever going to be the answer - as it brings in its own set of potential problems and drawbacks. I'm very comfortable using epoxy and have for 40 years, ever since I was a sculpture major in college, but if I had a canvas canoe to fill, I think I'd stick with the traditional fillers.
 
I did a bunch of freighter canoes last summer with epoxy filler. It worked well enough and there were circumstances which deemed it an appropriate choice.

However, it is a lot more work to get smooth enough for paint than well applied traditional filler. I can be done applying traditional filler in a couple of hours and it will be surface quality fine enough for just basic sanding. OK so I have to wait a couple of weeks till I can paint, but that is a scheduling issue and I can do other work. With the epoxy I have to wait a week till I can sand, and then its a whole lot of sanding till its ready for paint.
 
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