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Canvas Dilemma

Discussion in 'Wood and Canvas' started by NickD, Jul 24, 2017.

  1. NickD

    NickD Recreational Sander

    So… Just completed my second restoration: a 1919 16’ OT OTCA (made an appearance at this year’s Assembly) and had an issue with the canvas that comes and goes. Here’s what happened including facts that are either pertinent or potentially interesting:

    · Canvas was stretched on the hull in April, I canvas with the canoe right side up, hammock style. I tensioned the canvas without canoe to make sure everything was even then relaxed the canvas, added canoe and re-tensioned. Temperature about 60 or so.

    · Tacked canvas starting from midship moving to each end, one side at a time, leaving the ends open where tacking became difficult.

    · Removed tension, flipped canoe and hand stretched (using canvas pliers) canvas at each end, tacking and keeping as tight as I could get it. Kept high tension on the extreme ends (mid stem) and worked the stem starting from the bottom around to the top. NOTE: I do all my work solo other than putting the canoe in the canvas initially. Also NOTE: Had an issue with the canvas rippling transversally near the bow and stern on the hull due to what I thought was “pull back” from the ends. I had to work the stretched canvas considerably (I thought) to get it smooth. This involved untacking portions, re-stretching and re-tacking. Also ANOTHER NOTE: Ends tacked and completed 2 days after the rest of the canoe was canvased and tacked, ie. total canvasing occurred over three days.

    · At this point canvas is complete, smooth, ends sealed with bedding compound and tacked. I filled the canvas with OT filler and let sit for 5 weeks until it was cured. NOTE: Had the text book ripple of canvas above each tack along most of the hull. At the ends, the ripple was biased to the nearest stem side of the tack.

    · Painted the hull. I sanded the filler lightly and put multiple coats of paint to get to the finish I was looking for. Paint: Interlux Dark Blue.

    · The morning after the final coat, I decided to move the canoe out of the garage for a little while to “air out”. That day turned out to the hottest and sunniest day of the year. About 3 hours later I returned finding the canvas/filler/paint rippled on the hull on the bottom and side facing the sun. The ripples ran transversally across the hull. Hull was very hot to the touch.

    · After a “stern” conversation with myself I expedited the canoe back to the cover of the garage and covered it with cold wet towels to cool it down. Ripples receded somewhat but not completely.

    · Over the next five days (in humid weather) the canvas gradually (miraculously) flattened out.

    · The canvas behaved at Assembly. And paddled quite nicely too.

    · Now, back in the garage, one side at one end has re-rippled mildly. Canoe hasn’t seen water since Assembly.

    Did I do something wrong or is there something I should have done better? How tight is tight then canvassing? My first restoration went very well and I’m worried I was a bit sophomoric on the second go-around. If I let the paint cure longer, protected in the garage, would that have prevented the rippling which I assume was caused by the expansion of the dark, heated, not completely cured, painted surface? I'm thinking that if the canoe gets wet again or it gets really humid, it may flatten again.

    On another note, the day before we left for the Assembly, my wife made an impressive canoe bag/cover out of white bed sheets that survived the trip up to Assembly and back in glaring sun in an effort to prevent re-occurrence. It worked really well.
  2. MGC

    MGC Scrapmaker

    Every now and then problems can rear their ugly head...
    Your canvassing process sounds quite normal although you do not mention placing any weight in the hull during the stretching and canvasing. I normally put a few bags of sand or cement inside the canoe while it is sitting inside the lengthwise stretched canvas. I'm not sure what would happen if you don't do that? It's possible that it would make no difference if you consider the upside down method as an alternative. There the canvas tightness relies on the stretching and "pucker" without any vertical force applied.
    I also tend to cure the filler a bit longer than you did. Although I know that folks do sand and paint sooner I tend to let it sit for at least 6 weeks and possibly more. Paint is not likely to be your's (in my opinion) more likely how you stretched the canvas and the filler.

    At this point you are sort of committed to the result. What you can do is to always try to paddle with the puckering side away from the sun or more realistically you might try to re-tack the canvas. There are and have been builders that re-stretch and re-tack after the filler is dried.
  3. Paul Scheuer

    Paul Scheuer LOVES Wooden Canoes

    I might have missed it, but I didn't see the "wash down with hot water to slightly shrink the canvas" part. Was it done ? (For the record, I've never re-canvased, but there is one in my future).
  4. Howie

    Howie Wooden Canoe Maniac

    For what it's worth... I had a wrinkle problem a while back that sounds a little like yours - except that mine showed up a few days after I mudded it. Only time I ever had a problem. I ended up ripping it off & doing it again. At first I could only think I got a batch of bad filler, or maybe the weather was too extreme (we went from 70 deg to 30 deg in a few days), but in retrospect that seems unlikely and I've always wondered what went wrong. I started to wonder if when I folded the canvas I didn't have the sides the same length. After thinking about it I changed my procedure a bit. Here's a few things I do now:

    1) DO NOT assume the ends of the canvas were cut at 90 degrees to the length. I now fold the canvas in half along where the keel would lie, line up the long sides together, then clamp both ends. This will cause both sides of the canvas to be the same length and thus stretch the same. But be careful not to cause a sharp crease when you fold otherwise you'll have trouble causing the crease to lie flat against the canoe when stretched.
    2) When you place the canoe in the folded canvas take pains to center the canoe as well as you can to the canvas. Again, you want both sides to be equal length so they stretch the same.
    3) I canvas with the canoe keel-side-down and the canvas tensioned with a come-along. I start with 40# weights at both ends of the canoe and just a little tension. I then use a canvas puller to get rid of side wrinkles. But I don't staple yet - I use clamps to hold the canvas in place.
    4) After that I place more weight at the ends to a total of 120# and increase the tension. The canvas should 'ring like a drum' when thrummed. I let it hang under tension for at least an hour.
    5) After it has hung for a bit I REDUCE THE TENSION a bit just enough so that I can pull the canvas at the tips and cause the canvas to lie flat to the canoe's sides in this area - on some canoes with nice compound curves at the tips you'll never get the canvas to lie against the canoe in this area if the tension is too tight.
    6) Then before I start tacking the canvas down I reduce the tension again. Add a few tacks/staples in the stem area right where the canvas stops conforming to the stem shape. This will help prevent the canvas from 'bouncing back' when the tension is removed.

    Anyway... just FYI I guess.
  5. OP

    NickD Recreational Sander

    Thanks for the replies! MGC, I do put weights in the canoe as well as use braces from the ceiling to keep the canoe seated in the canvas. Howie, thanks for your canvasing steps. Going to have to look into that the next time around. I'm beginning to think this is a case of not the right tension on the canvas and filler that may have wanted to cure longer. Sun definitely played a part since as of today, the side that got the sun is much worse than the other side. Either way, a good learning experience for the future when I recanvas... In the mean time, since it had smoothed itself once, I'm going to wet the inside of the canoe/canvas to see if any swelling/shrinking will temporarily solve the problem again. Maybe I have a rainy day - humid loving canoe!

    Plus, glass half full, since I know I have a redue in the future, time to go see for myself how durable canvas/filler/paint really is!

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