Using Dacron

[paul buettner]

This is my first post. I'm looking for ideas, tips/tricks, etc. I have designed & made 2 canoes using dacron as a hull covering. I felt I had been careful especially the 2nd time to fair the hull & get it very smooth. Then I applied 1 coat of linseed oil. After it had dried on, I applied the dacron using the method described by Alex Comb in his excellent article "Dacron -- A Canvas Alternative" in Wooden Canoe Issue 142, August, 2007. I really like the process and the non-toxic, water-borne filler Ekofill from Stewart Systems. But I would like to correct a couple of small problems if possible.

1) After filling the dacron as recommended and then varnishing the inside of the hull, when I flipped the canoe over again to paint, I noticed a couple of small "blisters" in the surface. These were not evident when applying the filler but only after it had dried on several days while I worked on the inside. I have thought that the cause might be the use of the linseed oil on the hull prior to covering. There may have been a couple of small spots where the oil was not fully dry/cured, and thus leached thru the dacron cloth, preventing the water-borne filler from adhering completely to the cloth in those spots. I'm considering varnishing the outside of the hull next time instead of using oil. Good idea? Or varnish over oil to ensure a dry surface under the cloth? Anything else to do before putting on the cloth?

2) I used 3.7 (or 3.4?) oz. dacron I purchased from Alex. It is very nice to work with, but it DOES NOT hide any imperfections. Even some of the wood grain shows thru the filler and paint (4 coats each). Especially noticeable are planking lines pretty much all over the canoe, plus a few small tack dimples, etc. This sort of thing might just "go w/ the territory" of using dacron. But I wonder if there is anything I can do differently or better to minimize these things showing thru, so as to get more of a "showroom finish". I hesitate to use a wood filler for additional fairing of the newly made hull. Plus, it seems to me that using fairing compounds will inevitably fill in the small gaps between planks, which allow for some expansion without buckling. Would it be better to use a different filler on the dacron? More filler? Combination of the Ekofill and something else? Double-layer the cloth (doesn't seem practical)? . Any thoughts?

I'd like to work out for myself a likely approach before making my next "baby". Tks. very much!

Paul Buettner

 

[peter osberg]

Sounds like a paint incompatibility. I used epoxy with and without graphite powder (for abrasion) as the filler, which solves the problem of the paints fighting and provides a hard outer coating. I posted my routine (not eco-whatever) on this forum a few years ago, and am still happy with its longevity.
peter

 

[paul buettner]

Tks for your reply. Yes, I had also been thinking it was the incompatibility of the oil on the hull under the dacron with the water-borne filler I used on the cloth that produced the little "blisters", or areas where the filler itself just didn't "take" to the cloth & so separated out like that. That's why I plan to use varnish over the hull next time under the cloth. I have also seen a post or 2 that recommended the use of a paste wax over the varnish. Sounds like a good idea to get a really smooth, slippery surface that way. Do you know if the wax also serves the purpose of "filling in" things like planking lines & small tack dimples?

I'd be interested to know more about your use of epoxy w/ graphite or some other powder (e.g., wood flour?) as a filler. Are you talking about using the epoxy filler directly over the hull as a fairing material or as a filler with the dacron cloth already applied? I have never worked w/ epoxy, but that doesn't mean I can't learn. I do really like using the non toxic Stewart Systems ekofill on the cloth. I wonder about using something like a fairly thick latex primer over the filler as an additional filling layer under the paint. Could be that might cause more incompatibility problems w/ the yacht enamel paint? But I haven't noticed any compatibility problems using the paint directly over the water-borne ekofill, as long as the filler has had enough time to dry out well.

Any more thoughts? Tks again.

Paul

 

[tonycondon]

Paul,

Have you tried contacting Doug Stewart with your questions about compatibility? I use the Stewart Systems to fill and paint the Dacron on my wood Sailplane last winter and found Doug to be very helpful and usually quick to respond to email.

I really like the non toxic system as well. We covered the control surfaces in my apartment!

http://cherokeesailplanes.blogspot.com

 

[Todd Bradshaw]

Telegraphing surface irregularities is simply one of the characteristics of Dacron canoe covering because it's so thin, and there really isn't any way to get around it. Even if you had the hull perfectly fair and smooth (sanded, faired, filled or whatever) thin hunks of mechanically-fastened-together wood (which is what the hull is made from) tend to move a little bit with changes in temperature and humidity, so it probably wouldn't stay perfectly fair and smooth for long. The thin layer of Dacron covering it would then quickly show these changes.

Heavyweight cotton canvas and filler makes a skin that's much thicker than filled 4 oz. Dacron and with that extra thickness, you get a fair amount of hiding power. In drastic cases, it will also show planking irregularities, but to a lesser extent and a lot of the small ones won't ever be seen. It's all just one of the trade-offs that thin skins bring with them and doesn't reflect on your craftsmanship. Back when Old Town was offering their "Featherweight" model (15' "Lightweight" hull with Dacron covering, instead of canvas) they always cautioned that the skin would tend to show the same sorts of irregularities that you're dealing with.

As to the paint problem, I haven't ever covered a canoe with Dacron, but I do use a couple hundred yards of 4 oz. Dacron every year, and oil on Dacron generally creates some sort of problem. It tends to soak in and spread down in the fibers where it's very hard to get out completely and it will repel most non-oil substances, including water-based products, most adhesives and to some extent, even epoxy resins. It also tends to stain from the oil and that seems to often be able to come through most coatings. I think I'd keep oil (and linseed oil in particular because of it's slow drying rate) as far from my Dacron skin (especially in unfinished, unfilled condition) as I could get it.

Linseed oil is also pretty good rot and mildew food. I don't know what state your Dacron comes in (the finished fabrics are always a combination of weaving the polyester fibers and a certain amount of finishing processes like heat-setting, coating, etc.) but oily Dacron is fairly likely to mildew in time. Unlike cotton, mildew doesn't actually eat Dacron, but it can work its way down between the fibers and grow there just fine. This might eventually cause stains or paint problems if it really gets going. So if you plan on oiling the hull, I'd be sure to give it plenty of time to dry before the covering goes on and there certainly might be other sealers that get along better with the Dacron cloth.

 

[paul buettner]

to Tony

Tks for the idea about contacting Stewart Systems re compatibility. I'm sure they would be helpful, and you are right, they were quick to respond to a question I threw @ them a couple of years ago. Actually, I think that's not such a hard problem to solve. I just coat the hull w/ a couple of coats of thinned varnish as a protectant & to provide a smooth, hard, dry surface over which to apply the cloth. Once the varnish is well dried, there shouldn't be any issues filling the dacron over it w/ the water-borne ekofill. Too, I have now found another helpful post on the forum from a couple of years back about using paste wax. The desired goal seems to be to get an ultra smooth, slippery surface under the cloth. You don't want the cloth "sticking" to the hull in places, except where you glue it in place along the sheer & @ the stems. The same thread also contained a helpful tip about using a primer over the ekofill that will build up a little & help cover "imperfections" better than the ekofill alone. Unless I hear about something better, that sounds like a good process that fits very well to what I am already doing. While I do appreciate the hardness & toughness epoxy offers, I'm not crazy about using it. Plus it seems to me it would also adhere thru the cloth to the wood hull itself. Partly just for purposes of repairability down the line, I'd like to leave the cloth skin effectively unattached to the hull, only just stretched over it. If that makes any sense. Yes, I agree about how nice that low toxicity of the ekofill is for the working environment -- and the lungs. Plus it's nice stuff to work with, period. I guess the only real issue w/ using dacron together w/ this kind of filler is that it makes for a pretty thin skin over the hull, which, I guess, offers a bigger potential of damage from sliding over the occasional rock, etc. But I think the stuff is repairable if properly filled & painted, and the extra layers of latex over the filler should also offer a little more protection. So far, in admittedly short & limited experience, I haven't encountered big problems of that sort.

anyhoo, tks for your ideas. And for letting me "think out loud" the way I just did. Helps to bounce ideas back & forth.

Paul

 

[paul buettner]

to Todd

Tks so much for your detailed & knowledgeable reply. Helps me a lot with both of the questions I originally posted. I do find I'm not all that much bothered about the look of plank lines & dimples showing thru. It really doesn't look all that bad, and I had pretty much felt it might just be that kind of necessary "trade-off" that comes w/ using thinner, lighter materials. Trade-offs of all sorts are definitely a familiar part of the craft of designing & building canoes, as I am already learning to appreciate. That also makes the process so much fun & interesting to me. As to the compatibility issue, I have already decided not to use oil on the next canoe. I'm quite convinced that the thing you said is exactly what happened in my case. It wasn't a horrible result I had by any means, but those few problem spots I described are, I feel, exactly where the linseed oil seeped into the cloth fibers from the hull. After all, that stuff doesn't really "dry" so much as just penetrate. Anyway, I don't want that seepage happening again. That shouldn't be a problem if I stay away from using oil, as you suggest.

Tks for your help & encouragement.

Paul

 

[Ken Fischer]

To deal with compatibility issues and as a sealer, have you considered dewaxed shellac (Zinsser Seal Coat)? It's easy to brush on, dries in a half hour, builds pretty well, is non toxic and sands well. The latest issue of Fine Woodworking claims it's more water resistant than spar varnish. It's traditionally been used between coats of materials that present compatibility problems like old finishes on furniture that's being restored. I just put two coats on the freshly sanded canvas of an old Carleton I'm repairing before painting it.

 

[paul buettner]

to Ken

Tks for the helpful suggestion. I recently found a thread (March 30 or 31, 2008) entitled "dacron on Old Town" that described the use of a "Zinsser 123" white primer over the ekofill filler I already use. Is this the same as the "Zinsser Seal Coat you suggested?" Sounds like this stuff is definitely worth trying, even for reasons beyond just solving compatibility issues. Just to be clear, tho, I have not noticed any problem using the oil-based Epifanes Yacht Enamel (heavenly stuff!) over the water-borne ekofill filler, once the filler was thoroughly dry. But, again, it sounds like there are other benefits to be gained by using the Zinsser beyond just helping w/ compatibility. One very important benefit I can think of is just that little extra layer of protection from the inevitable encounter w/ a barely-submerged rock here in N. MN canoe country.

Again, tks for your help. I do believe I will try this.

Paul

 

[zutefisk]

Varnishing the interior can soften a waterbased filler raising blisters.

I have run into this in areas where the thinned varnish tends to pool a bit like along the stems.

 

[Dave Wermuth]

different

The Zinsser seal coat is shellac and the Zinsser 123 is a latex primer. Two different kettle of fish.
Zinsser makes all kinds of paint ish stuff.

 

[peter osberg]

It is critical that the fabric does not bond to the underlying wood, so that flexing and expansion of the wood can occur. Canvas achieves this by being thicker and not fully saturating the innermost layer with the filler as to cause adhesion to the wood (the downside is it wicks up moisture, hence the rapid weight gain of the canvas covered canoe when wet). If you use epoxy as a filler, then you need to ensure that a barrier exists between it and the wood, as it will fully saturate the fabric.

 

[paul buettner]

to Zutefisk

Good point. I had thought of that possibility, too. To avoid possible problems w/ thinned varnish "seeping thru the cracks" to get thru the cloth under the water-based filler, I believe I'll just carry thru w/ the inside & finish that first before working on the outside w/ cloth, filler, & paint. Tks for the suggestion.

Paul

 

[paul buettner]

to Dave

Tks for the info about Zinsser. I'll look into this, probably get more info from them. Any "down side" you can think of in using shellac between water-borne filler & oil-based enamel? Sounds promising. Tks.

Paul

 

[paul buettner]

to Peter

I agree about not wanting the fabric to bond at all w/ the wood hull. I guess that explains your earlier reference to using "saran wrap" between the hull & the dacron before using the epoxy filler. I'm still reluctant to use epoxy but will think more about this.

Paul

 

[Dave Wermuth]

beats me

"Any "down side" you can think of in using shellac between water-borne filler & oil-based enamel?"

I don't know the answer to that one. The zinsser can says enamel sticks to it but I've only heard of shellac being used like varnish or as a bottom paint in areas that get scratched more frrequently.

 

[paul buettner]

to Dave -- RE "beats me"

I was also thinking about Jerry Stelmok's ("The Wood & Canvas Canoe") references to using the (probably much older formulas) "orange shellac" as a "bottom paint" on canoes that are going to be regularly submitted to abrasion on rocks (dragged over them in shallow rapids, etc., etc.). He describes the application, & also mentions about how it likes to develop tiny "cracks" over a season's use. He said the guides that used those canoes generally didn't see that as a problem because the shellac was easy to renew/refresh between seasons, & any cracks just "filled in". A concern I would have for my own process would be the potential of a cured shellac formula "cracking" under a layer of paint, if it's used as a primer. Best approach for me might be to contact the Rust-O-Leum folks for advice if I seriously consider using the Zinsser shellac formula as a primer. It might be great. But I'm also thinking the 1-2-3 latex primer might present fewer potential problems in the long run. Since I won't be ready to finish a canoe again for some time yet, I think I'll just put off dealing w/ this until I need to buy something. I do like the idea of a primer over the dacron filler, tho. Tks for your thoughts.

Paul