Wood around windows, even the interior, easily gets damp due to insufficient caulking, heavy humidity and rain or condensation that forms naturally on glass. Frequent dampness can cause black mildew. If you notice the mildew stain quickly, it will be easier to remove. Sometimes, however, stains go unnoticed because the window is covered by a curtain. By the time you see it, the stain has had time to settle. No matter if it is a new stain or an old stain, you can remove the black mildew and return the wood to its natural beauty.
Rub a dry, mildly abrasive sponge over the mildewed area. This will loosen some of the black mildew. Wipe it off into a paper towel and discard in an outside trash barrel.
Slip on your rubber gloves. Mix 1 cup of household bleach with 1 to 2 gal. of water in a bucket.
Dip a soft sponge in this solution. Squeeze excess fluid out of the sponge before using it on the wood.
Wipe down the mildew-stained wood and then scrub heavily stained areas. Rinse out the sponge frequently or use a new one. Allow the solution to sit on the stain for a few minutes to kill the mildew.
Wipe the area well with paper towels to dry the wood as much as possible. Direct a fan towards the window to aid drying.