sunproof polyurethane?

Hi,
The front door of my house has valspar polyurethane with UV protectant over stain and every year the sun flakes it off. Is there something better so I don't have to waste all this time dinking with it?
Thanks
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A different brand of spar/marine varnish may last longer but, given enough time and/or exposure, UV is going to break down anything you put on.
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Mike G.
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I should add that if you have been doing it every year part of the problem may be insufficient surface preparation prior to adding a new coat.
Putting a finish over a failing finish with out good preparation can weaken the new coat's ability to adhere. It will only be as good as the grip the coat underneath it has on the wood.
Further varnish doesn't stick well to already cured varnish. Some sanding of the whole surface has to be done to provide some tooth to the under coat so a good mechanical bond can be made.
Just some further thoughts
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Mike G.
snipped-for-privacy@heirloom-woods.net
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I have used Bristol Finish on a dark southern door with good results.\

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Even the best varnishes need to be "redone" every 2 or 3 years. Can you shade the door from direct sunlight in any way? Maybe an awning?
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Try Hydrocote Exterior. It's a water based poly. Excellent stuff. Highland hardware carries it. I've had it on for about 2 years on some fir exterior doors and they still look like the day it was put on. Until now, it was my best kept secret. SH

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Sorry, polyurethane (the chemical) is broken down by UV. It's a one way decomposition. The manufacturer can add chemicals to the urethane to delay the decomposition, but they won't stop it. The UV inhibitors work by sacrificially absorbing the UV. Once all the inhibitor has been broken down, the UV will start to work on the polymer.
Recoating works by laying down a new layer of inhibitor. You definitely need to sand before recoating, both to give the old varnish some scratches for physical bonding and to remove the surface oxidized polymer.
If you want a true outdoor finish, use marine spar varnish without polyurethane. It'll yellow (heck, it starts reddish!) like crazy and will still need recoating, but it should last longer than any PU. So-called outdoor polyurethanes are not good. Most, if not all, water based PU are actually emulsions of polymer in water. The solvent is different but the polymer is essentially the same. If it's PU, it's UV sensitive!
Philip
On 24 May 2004 15:25:57 -0700, snipped-for-privacy@rock.com (topdog) wrote:

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