QUESTION:
We have a black discoloration occurring on the wood part of the windows in our house. Do you know what it is and how to get rid of it? The windows are double-hung and the house was built in 1995. I assumed it was mold and moisture-related because I noticed it first in the bathroom, but now I have found it in small patches on other windows. I have tried many cleaning solutions including TSP and a bleach-water mix, but none seem to work. It occurs both in winter and summer, with windows open or closed.
ANSWER:
If the stains are a dark discoloration that cannot be removed from the surface, you have water damage in the wood. If the TSP removes the stain it may be dirt or mold. Once the surface finish is damaged by water, the water will discolor the wood. If the finish is gone and you have a dark stain, you have water-damaged wood.
The fix is to refinish the wood by sanding, bleaching, and more sanding. Then stain and varnish back to the original finish. It’s not an easy job. Don’t get too worried about the “mold” word. Issues related to mold have been greatly exaggerated by many folks in recent years. Go to the State of Wisconsin or university websites for accurate information about mold in a home – not testers or contractors who make money on mold.
When installing carpet or floor covering on a concrete basement floor, always try to add some type of insulation. The concrete slab is in contact with the damp soil. This will make the floor covering cool and subject to condensation, resulting in a musty, mildew smell. A little insulation will make a huge difference.
Mildew or mold will always grow on exterior surfaces that don’t see much sun – at least in our Wisconsin climate. I would definitely wash with a 
