I was just cleaning the windows in my bedroom and my daughter when I noticed mold on the top of the bottom window, where the lock is, in that area across the whole length. Only on two of mine, I have three and on both of my daughters. These windows are anderson and only a few years old we replaced them ourselves.My husband says that it is from the airconditioners in the summer. These are the only windows that have this and we have replaced all the windows in the house They are wooden windows. Does any one have any ideas as to why this is happening or how to prevent it.

 

There could be several reasons why this is occuring, but basically it is because conditions in that location are right for condensation to occur. Commonly you have cold air falling off the upper glass, as it falls it meets warmer air. If you have forced air heat, the lower sash blocks air movement and the top of the sash near the meeting rail rarely gets any warm air moving over it. This can result in a confined area of condensation, and anywhere the humidity is higher than 60%, mold can grow.

This condition might be aggrivated if the windows are left unlocked, allowing warm/cold air to mix at the interlock. It might also be more noticable if draperies or blinds are left closed. Often it is more noticable on one side of the house due to a lack of sunlight to warm or dry the windows.

The solution to this would be to wipe the woodwork often, not allowing the mold to propegate. Tilex would be an appropriate cleaner that could be used sparingly on finished woodwork. Cleaning the mold before it becomes a larger problem would be important because if the mold begins to feed on the wood underneath the varnish, then you have a bigger problem that would require stripping and sanding to get rid of the mold stains. Keeping the drapes or blinds open would also help. Running fans in the room when condensation is a problem will also reduce the likelihood of mold growth, because moving air will warm the windows and circulate the conditioned air in your home. Keeping the windows locked when they are not in use will help reduce air infiltration. Hope some of these suggestions help you out.