With all the new products out there, it is hard to find a finish that is best for new wood windows. The windows are nice, fiberglass outside and clear pine inside. What should I use to stain and seal the windows interior? Taking into account window condensation and UV protection. I have used stain and urethane in the past, and after a few years have had dark streaks near where the wood meets the glass, from possible condensation soaking into the wood, I have also had some flaking of the urethane due to UV most likely. I just would like to know the best practice these days…..
The stain can be an oil based wiping stain. For a deeper color use a penetrating or gel stain. For the finish I like <a href="//www.painters-toys.com/clear-wood-finishes/oil-base-varnish.html" target="_blank">McCloskey Man O'War Spar Marine Varnish</a>. I think it is still the best.
The dark streaks is from water getting into the wood behind the finish. This can be prevented by applying a small bead of paintable clear caulking where the wood and glass meet. The same water can also cause some or most of the flaking.
All clear finishes break down eventually from water and UV light. Maintenance of the finish is needed every few years. I think the marine spar varnish is easier to maintain.