Surfaces that constantly are damp provide the ideal growing conditions for black mildew. The condensation that naturally occurs on windows runs down the pane and lands on the wooden window sill. This makes the wooden sill damp and increases the chance of black mildew growth. The mildew can stain the wood window sill, spread to other areas of your home and fill the air with an unpleasant musty odor. Once you find black mildew growing on the window sill, remove it as soon as possible with a few household items.
Fill a spray bottle with white vinegar. Alternatively, mix 1-cup oxygen bleach with 1 gallon of water and pour in a clean spray bottle. Neither vinegar nor oxygen bleach will damage, discolor or harm surfaces.
Spray the mildewed window sill with the mixture and let sit for 10 minutes. Dampen a clean cloth in cool water and wipe the mildew with the cloth.
Fill a bucket with 1-gallon warm water. Add 1-cup borax to the water and mix thoroughly with a long-handled spoon. Saturate a clean cloth in the mixture and wring out the excess liquid. Scrub the windowsill clean with the damp cloth.
Examine the rubber seal along the window. Wipe any mildew or mold off the seal with the damp cloth.
Dampen a clean cloth with cool water and wipe the mixture residue off the windowsill before drying it with a towel.