How Do I Identify Wood Rot or Mold in My Old Windows?

Check where the paint is cracked and gently probe the area with a screwdriver. If it’s soft, that's a sign of rot. You'll need to assess how bad it is to decide what to do next. Don't forget to check what caused the damage initially, that’s super important!

It sounds like you’re dealing with mildew, which is quite common in old single-pane windows due to condensation. You should strip the paint down completely—using a drill attachment like this one can help make quick work of it. After that, think about applying Minwax Wood Hardener; it really helps solidify any soft wood. Then just sand, prime, and paint!

You won’t know for sure about the wood until you scrape off the paint. Grab a flat putty knife and try peeling some of it away to see what’s underneath. The fuzziness could be either mold or something else, but it's hard to tell just from the picture. Good luck!