Water based polyurethane for exterior finish
 

I've been building a backyard gazebo for a client part time for a couple of years. He's a bit eccentric, the thing is way over built, or over designed anyway, but I'd like to finish it and have the pictures for my scrapbook.

He spent way too much money on mahogany doors and windows (it's enclosed) and the oil based polyurethane degrades in the sun way too quickly for my liking. Re-coating the thing every year is just not preferable.

The fellow at the local hardwood supply outlet swears that water based polyurethane lasts 4 or 5 years under UV before needing re-coating. I used it for some mahogany on a shower seat and floor grate in a bathroom that has no curb or curtain, the entire floor is the shower bottom and drain. Again, this was on his advice for longevity. That stuff has been in for a few months so I don't know yet about long term performance.

Anybody experienced with this stuff? It's sure nice to use.

Water based varnishes don't add character to wood the same as oil or even polyurethane, something to consider with mahogany. Try a test piece before you coat the whole door. A varnish for marine use might work better.

That's what I would have thought but the mahogany I used it on for the bathroom job came out looking all right.

I don't know about finishes for wood, but I think water-based paints tend to be more durable in exterior applications. I think it's bcause they have better elasticity than oil-based paints. The latter get brittle after awhile and begin to fail.

Could be. I know this spar type varnish is not lasting in the sun worth a damn. Brittle and chipping.

If you really want to know call up these guys:

http://www.fpl.fs.fed.us/

The government pays them to figure these things out. I don't think they get a lot of calls so will be happy to talk to you. I called them once about one of their reports and they connected me to the guy who wrote the report.

Mike