Surface mildew is quite easy to eradicate with full strength white vinegar. If your bathroom walls are full of mildew, wipe the mildewed spot with a vinegary rag, says an environment Residential Cleaning Service in Evanston, Il. You could also spray on the vinegar, let it sit for a few minutes, then wipe it dry. If the mildew has left a stain, try spraying hydrogen peroxide on the spot, waiting a few minutes, then rubbing the area dry with a clean cloth. Repeat as needed. Be careful, though, because hydrogen peroxide is a bleach, and it may change the color of the paint. Test the peroxide on an out of the way area first.
If you have very persistent patches of mildew, try this. Put some white vinegar in a glass jar and add an inch long section of copper wire. Let it sit for a few days, then pour the vinegar into a spray bottle, leaving the copper wire behind. Do not leave the copper in the vinegar longer than a couple of days, or too much copper will dissolve into the vinegar and you will end up with a solution that will dye your walls a bluish green.
Use the coppery vinegar to clean off the patches of mildew. Copper kills fungi, and the tiny bit of copper that has dissolved into the vinegar will help prevent the mildew from returning. Wipe the walls dry. Rinsing is unnecessary.
Long term patches of mildew can be scrubbed off a wall or out of grout with a scrub brush or an old toothbrush dipped in a paste of borax and water. If the mold has penetrated the wall, leave the borax paste on the wall for a couple of days before vacuuming it off, says an environmental Residential Cleaning Service in Evanston, Il. If you allow mildew to grow unchecked for a long time, it can penetrate the wall very deeply. If a coat of stain sealing paint cannot solve the problem, you may need to replace the wallboard.