Polyurethane on Windows

Old 06-17-08, 02:29 PM
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Polyurethane on Windows

Hi all!

Our casement windows are in need of a coat of a finish on the inside bottom rail. The moisture from the last (very cold) winter we had left the old finish peeling (polyurethane).
The windows were originally finished with laquer. I was going to try Spar Varnish but was afraid it would react with the lacquer.
Some of the rails are down to bare wood. Can I just go over this with the polyurethane or does it need to be sealed first?
I have used the poly over the lacquer before without any problem...


Old 06-17-08, 03:26 PM
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Be sure to clean off all the old loose finish. Anything that is loose will come off later, with the new finish. Poly should not affect lacquer.
Old 06-17-08, 06:12 PM
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And by clean off the old finish, he means lightly sand the trim with something like a fine Sandblaster sanding sponge, or maybe some 220 grit sandpaper. If you get down to bare wood, apply some stain to the wood, then allow 24 hours dry time. You can use almost any finish over lacquer provided the surface is lightly sanded and clean- so yes, you could use polyurethane if you want, but you are right- that spar varnish might last longer.

Whatever you decide to go with, apply at least 3 THIN coats, sanding lightly between each coat of finish.
Old 06-17-08, 07:11 PM
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choice of coating UV???

A major issue on interior window finish is whether the moisture caused the problem or the sun. UV can be really tough on finished wood causing the finish to peel and crack before it's time.

If your windows have UV protection (LOW-E) this isn't a problem. If you windows are just insulated glass, they ask the paint store for a finish product that will hold up to UV rays. This will extend the time before you have to finish them again.

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