Canvassing with untreated, unshrunk canvas

[Jerry Fruetel]

Until now, I've canvassed canoes with preshrunk, mildewcide treated #10 cotton canvas. On my next canoe, I may use untreated, unshrunk #10 canvas. I'll treat and shrink it on the canoe the after canvassing. I'd appreciate feedback from any one who's done this.

- What mildewcide did you use, if any, and how did you apply it?
- How did you shrink the canvas on the canoe?
- How much less tension should I apply, compared to preshrunk canvas? I typically stretch preshrunk canvas along the gunwales until it almost rips, and that's worked well, but I don't know how much to back off from that with unshrunk canvas-- a little? a lot? Obviously, I want to avoid stretching it so tight that it pulls out the fasteners when it shrinks.

 

[Paul Miller]

Hi Jerry,

Sorry to see no one has yet given you a reply.

I have always used untreated #10 and used traditional fillers with mildewcides in the filler.

I don't believe treated canvas is preshrunk. When it's wet from whatever reason it shrinks and when dry it relaxes.

I don't think you need to stretch the canvas to the verge of ripping, that sound too tight to me, but each of us has our preferences. I do fill the canvas on the same day I canvas the canoe. It will not matter if it's humid or dry as long as I canvas and fill on the same day. The canvas will not relax once filled.

Good luck,

Paul

 

[Andre Cloutier]

Jerry,
the method i was shown and have always used is to stretch as you have done, but not excessively. When the boat is done, apply a zinc napthenate liquid product, as they use for preserving canvas articles. Most hardware stores sell it. This will thoroughly wet the canvas, and take about two or three days to dry completely - outside, it smells too strong for inside. Wetting the canvas will have the effect of shrinking it when it dries, and you will see lots of puckers where you fasten at the rib tops. From here its fill, dry, prime and paint. I dont have much experience with traditional fillers, but the liquied zinc will make sure that it is treated right through, as the filler will likely not get through everywhere on the boat. hope that helps

 

[Jerry Fruetel]

Thanks, Paul and Andre. I've been unable to locate zinc naphthenate products in the States. Maybe I need to make a run north to Ontario! To reduce the smell indoors, perhaps I could apply the zinc naphthenate only along the sheer and stem, where mildew would be most likely. And use plain hot water to shrink the rest of the canvas. Then put a locally available mildewcide in the filler and also in the thinned marine varnish I use to sealcoat the hull exterior. What do you think?

Andre, it sounds like you don't initially stretch the canvas so tight that it creates puckers around the sheer fasteners-- your puckers appear only after the liquid naphthenate product dries and shrinks the canvas. Am I right about that?

 

[Andre Cloutier]

Oh, i stretch it alright. I know some advocate not stretching, but i use a come along and stretch it out well. But as you cut the boat out at the ends, it relaxes and you have to go back a few to straighten it out. Thats where the wetting really helps it shrink. Remember mold is an organism and needs a food source, which the canvas is since its a woven cotton product. You could put something in the filler, but its the canvas that will mold and dry rot (which is a form of mold). Same reason i wont put linseed oil anywhere near wood, unless you want it to eventually turn black with mold.
try this
http://www.defender.com/product3.jsp?path=-1|10918|2303285|2303289&id=25451

most puckers appear later, but the gunwales do a good job of covering them.

 

[Jerry Fruetel]

Have you used the Canvak product you linked to? It contains paraffin wax as a water repellent, which seems like it might interfere with filler penetration.

 

[Dan Miller]

Back in the day, paraffin dissolved in gasoline was used to waterproof traveling circus tents. Can you say "Poof?"

Back on topic, I had the same question about what was used to give this product water-repellency. If it is not paintable, I'd be cautious about using it. Test pieces definitely in advance.

 

[Andre Cloutier]

know nothing about it, but no use posting a link to what we buy here in Canada. Just demonstrating you will find what you are looking for if you are persistent.
Maybe the vapour from those old tents helped make bears riding bicycles make sense to the ticket holders?

 

[Todd Bradshaw]

Do not try to paint or fill over Canvak. It won't work. Use it instead on your Teepee.... though not on your TP.....that won't work either.

 

[Jerry Fruetel]

Thanks all. If anyone knows of a decent canvas mildewcide available in the States, let me know.

 

[Dave Osborn]

I could see applying Canvak to the hull planks prior to canvassing....

I was taught to stretch canvas tightly. I know there are those that hand stretch successfully.

I've never shrunk canvas..... If it is tight to begin with, why shrink it? How do you shrink it anyway? If I did it, how would I know it shrunk?

I won't canvas during high humidity. I've had two experiences, both outside. One during heavy fog, once under a tarp in a rain storm. The time in the heavy fog, the traditional filler was applied the same day. In a week, with dry humidity, the filled canvas was loose. Same with the rain storm canvas (sans filler). My (unscientific) theory is that the canoes had absorbed the moisture from the air and swelled. Once the hull had dried and shrunk, the canvas was loose.
Ultimately I unfastened it and stretched about an inch, maybe a little more, to get it tight again.
Still lotsa mysteries in this old wood canoe world!

 

[Larry Westlake]

cotton stretch

I Once the hull had dried and shrunk, the canvas was loose.

Cotton shrinks when wetted, but relaxes again when dry. If its the first time the canvas has been shrunk, it will keep some of the tension when it dries, but not all of it, relaxing back a bit. After that the the cotton shrinks then dries back and forth between the same two sizes. In other words, it doesn't keep getting smaller. Lucky thing!
Anyone who has stretched their own canvasses for painting with acrylics (water based art paints) will probably have noticed this. If you ever use cotton sash cord for tying things outside you will also see the dynamic.

I no longer do mechanical stretching for canvassing my canoes, I just hand-stretch. Since an over-eager stretcher can get enough (too much)tension so that light cloth rips at some staples when wetted, I figure its enough.

The two reasons I give myself for wet-stretching on the boat are: to equalize the tension of the cloth over large areas of hull by the pull-and-relax of the shrink-&-dry cycle; and to reduce the amount that the filler-loaded cloth moves upon first being wetted. But there's no science there, its just feely.

 

[Jerry Fruetel]

But there's no science there, its just feely.

Yes, indeed, there is a lot of ‘feely’ involved. I just finished canvassing a new Atkinson traveler using untreated #10 Midwest cotton duck. It turned out well, and I learned some things along the way.

I experimented first on three 8” x 20” canvas strips. I liberally applied room temp water to one, boiling water to another, and water + steam iron to the third. After air drying, they all shrank the same amount—3% in length, 1% in width. I was a bit surprised that hotter temps didn’t increase shrinkage.

It was surprisingly difficult to get water to penetrate all the way through the canvas, despite liberal wetting and vigorous rubbing. I’ve read elsewhere that the initial wetting swells cotton canvas fibers, which tends to inhibit further water penetration. It’s no wonder most canvas fillers don’t penetrate all the way through.

The difference between length vs. width shrinkage (3% vs. 1%) also surprised me, but I guess experienced weavers know all about it. Apparently it has something to do with the warp and woof, and the mechanics of weaving. Don’t quote me.

I canvassed the canoe right-side-up, applying tension horizontally with a come-along and vertically with weights. I used a vice-grips type canvas stretcher when tacking along the sheer. I’d guess I tensioned everything about 90% as tight as when using pre-shrunk canvas. In other words, pretty darn tight, but not ‘about to rip’ tight. That’s the ‘feely’ part.

After adding M-1 Advanced Mildew Treatment (Home Depot) to room-temp water, I liberally wet the canvas, went home and prayed to the shrinkage gods for mercy. I was concerned the canvas might tear away from the fasteners. After all, on a full size canoe, 3% lengthwise shrinkage is over six inches, and 1% width shrinkage is a half inch. Fortunately, when dried, the canvas looked great. The only noticeable change was the disappearance of the few little unwanted loose folds and wrinkles here and there along the sheer quarters.

I don’t know for sure whether M-1 mildew treatment will be effective. It’s intended for oil and latex paint/varnish surfaces, not canvas, and it could leach out over time. I added M-1 to the canvas filler, too, but fillers don’t saturate the inner canvas surface (nor did the old lead based fillers, so how much mildew protection did they actually provide?)

It’s fair to ask, why not avoid extra steps and uncertainties by using pre-treated, pre-shrunk canvas? That may well be the best advice. But, if for whatever reason you want to use untreated canvas, my recent experience says, “Go ahead, you won’t be disappointed”.

 

[Todd Bradshaw]

3% vs 1%:

When fabric is woven the warp (lengthwise) and weft (crosswise) yarns have to cross and in order to do so, one or both of them need to move a bit, up or down, to make room for the other to cross. They seldom move equal amounts and it seems fairly typical for most fabrics that the warp yarns tend to be kept under tension and pretty straight, while the crosswise weft yarns do most of the ducking and weaving (as it were). This tends to put more slack into the crosswise direction. In some cases, the fabric may even stretch a bit more or a bit easier crosswise than lengthwise. The warp and weft yarns are sometimes not even the same weight, which can also affect the fabrics characteristics.

Anyway, if we assume that the warp and weft yarns are the same raw material and similar in weight and we shrink the cloth, the fibers themselves should all shrink about the same amount - but - since there is more slack in the weft yarns as they go over and under during the weave, the cloth shrinkage may be less (or less obvious) than it is in the straighter warp direction where there is less slack. Three percent is pretty typical for cotton canvas products.

 

[Dave Osborn]

I usually use untreated #10 canvas duck. No wetting. No singeing. Just stretching with a come along and upholstering stretcher. I haven't noticed any issues on dozens of canoes.....maybe umpteen dozens.
I have tried wetting the canvas on a couple of occasions in the distant past, but have had problems getting the moisture beyond the sizing. It wants to bead up. What breaks the sizing to allow good wetting? Another question.....does singeing the canvas have any shrinking or relaxing of the canvas?

 

[Jerry Fruetel]

Good explanation, Todd. Thanks.

Dave, I noticed water beading on first contact, too, but with a little rubbing, the water soaked into the surface just fine. Yet it was difficult to get it to soak all the way through. Some DIY tent makers use untreated duck canvas with no waterproofing, and claim that the canvas does not soak through and drip except under heavy, prolonged rainfall. I tend to believe them now.

I singed my untreated canvas after shrinking it on the canoe. I didn't notice any further shrink/relax effect from singeing. I had hoped singeing would result in a smoother filled surface, but it didn't seem to, so I won't singe next time.

 

[Larry Westlake]

soakage

Jerry;
I am surprised that the temperature of the water was not important. But I wonder if hot water better breaks the sizing and increases penetration. I will have to test that.

I noticed that canvas resists wetting right through when I was doing penetration tests before using water-based filler for the first time. I was worried that the naphtha-vehicled preservative I use would make the canvas "greasy" and give poor bonding to the filler. To my surprise, the (fully dried) naphthenate acted as a primer, and filler penetration was so complete that unwanted bonding to the planking occurred. WITHOUT the naphthenate, it was almost impossible to get full-thickness wetting of the canvas by the filler - usually I couldn't even get the filler colour to SHOW on the backside of the canvas as more than pinspots. I had to wet-bag presoak the un-naphthenated samples overnight to obtain acceptable penetration. This may be because most water-dispersed paints now are not really water "based", they are resin-based paint emulsified in a water-based vehicle (I'm told). I suspect that as soon as the paint contacts a hydrophilic material the water-molecule jacket is stripped away from the
emulsified droplets of paint, and they coalesce and bond right there. They won't go any further into the cloth. Because a lot of the fabric volume remains unfilled, soakage weight increase after (test) "launching" was disturbingly high.

My reasons for using untreated canvas are that the poisons are applied ONLY where they are needed and I can avoid much contact with them. The scraps of untreated canvas are non-toxic waste. With treated canvas, I am forced into pretty intimate contact with the poisoned cloth, must breathe the poisoned lint, and offcuts are sent off into the world as toxic waste even before the sheath has completed its decades-long service life.

 

[Greg Hare]

I use one cup of white vinegar per five gallons of water to break down the sizing.
Greg