Polyurethane varnishes

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Glenn Adams
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Joined: Mon Sep 29, 2008 9:30 pm

Polyurethane varnishes

Post by Glenn Adams »

I've read in a book where the author spoke of using polyurethane varnish on the hull and trim work. He didn't go into details or give any specifics. I used regular spar varnish on my first canoe and had good results. However the varnish had a very short shelf life and had a tendency to start hardening in the can after it was opened. Is there any advantages or disadvantages to using polyurethane varnish instead of using spar varnish? I'm in the middle of building my second canoe and am debating using polyurethane varnish.
Rick
Posts: 727
Joined: Thu May 27, 2004 9:23 am
Location: Bancroft, Ontario

Post by Rick »

Glenn, if the varnish is drying in the can, transfer it to a smaller glass jar with a tight-fitting metal screw top and it should keep longer if the jar doesn't have much air in it.

Polyurethane varnishes are supposed to be harder and more abrasion-resistant than the traditional urethane varnishes. The polyurethane I'm using right now on paddles is Defthane and it does dry harder, but it also forms thinner coats which means more coats are needed. Maybe this is a characterstic of Defthane only, since I've used urethanes in all my other finishes. Maybe somebody else could comment on other brands.

Defthane brushes on easily and doesn't tend to run or drip... it doesn't need to be thinned so it's convenient that way. I haven't used it on a canoe, I don't think there would be any problems with it.
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John Caldeira
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Joined: Wed Aug 11, 2004 8:40 pm
Location: Dallas, Texas
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Converted!

Post by John Caldeira »

I really like using 2-part polyurethane fiinishes. It's main advantage over varnish is that is doesn't show scratches as easily. It also goes on thicker than varnish, so it hides minor sanding scratches.

Thinning it a little makes it easier to apply. Just keep the wet edge like varnish.

John
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