Sunday, April 12, 2009

Bark Canoe Sealant Dilemma

While up North for a short vacation (aka canoe time), I had to make another (regretable) decision regarding the sealant for the canoe. I had collected and purified plenty of spruce & pine gum last summer which had been stored in my city freezer all winter for this moment. Well I forgot to bring this vital item up and needed to seal the interior of the canoe while I had the time.

As a compromise and so as not to delay the build even further, I communicated with a few other builder who mentioned that they've used polyurethane sealants with much success in their bark canoes. It has many "advantages" over the natural sealants since it is apparently more flexible and isn't prone to running or cracking with temperature fluctations. It can also be applied in cooler temperatures when tree gum may set too quickly...another reason why it appealed to me at this time. Gidmark's books talk about Algonquin builder Jim Jerome and others using roofing tar as opposed to tree gum as well. Given that the bark quality isn't the best, I figured as much sealant assistance the better to keep this sucker waterproof. Still it pains me to use these synthetic elements in a boat made from natural, harvested materials - so as a compromise, I'll be gumming the exterior with my collected gum but decided to seal the interior with a synthetic agent.

The gooey tar was worked into the lap stitch seams as well as any other weak spots in the hull. In particular, the centre panel had many pin sized holes that I identified by shining a spot light on the underside of the hull and marking the locations where the light seeped through. These were sealed with single globs of sealant. The whole thing has made the interior pretty ugly, but of course it will be covered with beautiful cedar sheathing soon enough...

Interior "gummed" with synthetic sealant

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