What causes seal failure between dual pane glass?
There are basically two causes of seal failure. One is constant soaking of water that is trapped under the glass unit, which breaks down the sealant between the glass. The second cause, which I believe is the most common reason for seal failure in aluminum windows, and especially in wooden windows, is that moisture is allowed to penetrate through the sash and is trapped under the thermal pane unit, at the bottom. Those few nights that we get in the winter when it freezes, the moisture under the unit freezes and expands, subsequently popping the seal between the two panes of glass. On aluminum windows, not much can be done to prevent that problem. But on wooden windows, a top quality semi-glass latex enamel paint should be applied to the sash, with 1/6 inch minimum paint onto the glass. Getting the paint on the glass will seal the sash to the glass and not allow moisture to penetrate into the unit.
