Microscopic mold spores float in the air. Damp, poorly ventilated spaces with minimal or nonexistent light and greasy, dirty or grimy surfaces provide the perfect environment for mildew growth. A musty odor and a thin, white or bluish-green coating indicate mildew growth. If mildew grows on wallpaper, eventually it will discolor the surface and rot the paper. Cleaning mildew from wallpaper requires that the paper is waterproof or able to withstand contact with liquid.
Place a plastic drop cloth on the floor beneath the wallpaper you are going to clean to protect the floor. Pour 1 gallon of water into a bucket and add 1 cup of household bleach. Pour 1/2 gallon of water in another bucket and set aside for later. Open any windows or doors for ventilation.
Put on a pair of rubber gloves to protect your skin from the bleach and put on a protective face mask to keep from breathing the contaminants as you are cleaning. Dip the scrubbing sponge into the bleach and water solution and squeeze out some of the excess water so the sponge is saturated but not dripping.
Scrub the areas of the wallpaper affected with mildew. Work in sections if you are covering a large area. After you scrub a 2-by-2 area, dip a clean scrubbing sponge into the bucket with plain water, squeeze out excess water so the sponge is damp but not dripping and wipe the sponge over the bleach-cleaned areas to rinse.
Blot the cleaned and rinsed area of the wallpaper with a towel. Place a space heater in the area to aid with the drying process if the area is poorly ventilated.
Repeat Steps 2 to 4 as many times as needed to clean the entire surface that is contaminated with mildew.