A.Rot is a common problem on exterior window trim, especially brick molding. Not only is the trim exposed to rain and snow, but moisture from the interior often escapes between the window and the rough opening. This moisture condenses on the molding and rots it from the back. Brick molding should be back-primed before installation. Seal the ends of jambs and window casing with paint or varnish before installation. You could also set the ends into a bead of long-lasting caulk to keep the joint from trapping moisture.
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