Mold and mildew grow where there is moisture or high humidity. To reduce humidity in the home, use a dehumidifier or air conditioner, or ventilate with dry outdoor air. Increase air flow to problem areas. The source of the moisture must be stopped, or the mold will grow again.
Hard non-porous surfaces that have mold growing on them should be cleaned using a detergent and water solution such as borax and water. Minor mold infestations on painted porous materials such as gypsum wallboard can be cleaned using a detergent solution. Follow with clean water to remove any residue, and dry the surface. A chlorine bleach (sodium hypochlorite) can be used on the surface after cleaning. However, it may change the color of stained surfaces. Use a paint sealer to prevent the mold stain from bleeding through the new paint. Be sure to use safety precautions, and wear rubber or neoprene gloves and goggles. To protect from breathing in mold spores or fragments, use a minimum of a tightly fitted N-95 air filter mask available in hardware, lumber, or home stores.
Major mold infestations on painted surfaces may extend through the painted surface and into the gypsum wallboard or other porous material. The material needs to be replaced to adequately remove the mold. Applying chlorine bleach or other biocide does not neutralize the potential health effects of mold. Dead mold spores or mold fragments can still be allergenic. You want to remove the spores and mold fragments. A solution of 1/4 cup bleach to 1 gallon of water should be adequate for clean surfaces. The surface must remain wet for about 15 minutes to allow the solution to disinfect. Then dry the surfaces. Use fans and dehumidifiers or natural ventilation that exchanges inside air with outside air.