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Post by buckeye59 on Mar 23, 2005 11:03:13 GMT -5
Can anyone out there tell me why whenever finishing is discussed in my books only varnish is mentioned and not polyurethane? Is there a reason poly is not as good or were the books just written before polyurethane was on the market?  |
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Bannock
Wilderness Traveler
Posts: 56
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Post by Bannock on Mar 23, 2005 14:44:07 GMT -5
I've built a few canoes. I can't tell you answer for sure off the top of my head but here are a couple thoughts.
1) It could be a compatibility issue with the epoxy, and/or; 2) UV protection.
As of several years ago, I'm certain there was a concern with the compatibility of epoxy and polyurathane, that is, it didn't stick well. The poly would simply peel off in sheets. However, there has been so many advances in both poly and epoxy I don't know if that is still an issue.
The main reason, of course, that you want a layer of varnish over the epoxy is for UV protection so that the epoxy doesn't degrade. Spar varnish was made for this. I don't know if poly is. Certainly you'd have to look for an exterior poly that provides UV protection. I wouldn't use it unless it specifically states that it offers protection against ultra violet light.
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Post by Dan L on Jul 19, 2005 12:57:21 GMT -5
Again this is old but,
Bannack is right, you must use something that provides UV resistance to protect the epoxy.
As for traditinal varnish or poly, I believe most good marine varnish manfacturers offer both. Don't waste time on home center finishes.
As for one or the other, this comes from an Interlux rep, (Interlux is one of the 2-3 biggest names in marine finishes).
Traditional varnish wears out from the outside surface, as it gives up it's UV resistance. When it needs to be recoated, all it needs is to be sanded to provide a "tooth" and it can be recoated.
Poly varnishes wearout/deterate by cracking through the layer, and when they need to be refinished, to do a good job, all the old finish should be removed, making recoats a very large job.
Other then that, the polys are much harder and take more effort to sand between layers then traditional varnishes. On my 1st stripper, I figure using poly added about 1-2 months to the job.
On the current project, I'll use poly on the hull and traditional varnish on the trim.
Dan
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