Repairing Rotted Windows
Advice for rotting window sills.
Q: My family and I live in a 1930s-era home. There are a few windows that have rotting sills. We'd prefer not to have to replace the entire window. Are there epoxies that can be used to fill and reshape parts of old sills that have rotted?
A: Yes, you can use epoxy to repair a rotted sill of an old window, and that can actually be better than replacing the window. The great thing about using epoxy on a window is that you end up with something stronger than wood. Dig out the rotted wood and refill the cavity using products made specifically for this type of job. Go to a paint store and ask for a "restoration epoxy." Marine epoxies made for repairing boats are also effective.
If you do repair the sill, you'll want to figure out why it rotted in the first place and fix the problem. The No. 1 problem is neglect. If properly painted and maintained, a well-made wood sill can last 100 or 200 years. But if it's not maintained, water and weather will get inside the natural cracks in wood and cause it to rot. Another problem could be storm windows without weep holes, which are designed to move water away from the sill. And a third culprit could be an air-conditioner that sat on the sill and constantly dripped water on it. Without taking care of the underlying causes, you'll continue to have problems with rotting sills.