Painted surfaces support mould growth. The combination of cool surfaces and excessive humidity causes a high near-surface relative humidity and condensation. The condensation on your painted walls or window frames provides the environment that mould and fungus spores need to grow. To get rid of mould on paint you need to kill the mould and fungus spores without damaging the paint and wall board. Then you can make corrections in your living environment that will stop a reoccurrence of mould.
Clean the areas where mould is growing by wiping it with a sponge dipped in a mild detergent and warm water.
Allow the walls to dry naturally. If the moisture is still visible after 30 to 45 minutes, use a hair dryer on its lowest setting to dry the area.
Wipe the newly dry area with a sponge dipped in white vinegar to kill mould and fungus spores. You will notice some darkening of the painted surface, but it will dry and return to a lighter colour. The stain will need to be painted over, though, once dry again. Using bleach will damage most paints.
If your walls do not dry after 30 minutes you need to investigate for a leak or increase air circulation. You can purchase a mould testing kit at a large hardware store and send a sample of the mould in to be tested. Stachybotrys chartarum (black mould) can cause serious health problems. If your drywall is wet and weak you will need to replace it. The mould can be growing on the wall board and between the studs. Take steps to reduce a reoccurrence of mould. Purchase a dehumidifier. Insulate your walls. Speak to a heating and cooling company about cleaning your duct work and improving overall temperature control. Wipe up any spills immediately. Repair leaks. Replace windows.
At the first sign of mould in your home take all necessary steps to remove it. Mold has been associated with hay fever, asthma, inflammation of lung tissue, allergic skin diseases and disruption of cellular function. People with compromised immune systems are more vulnerable to the effects of moulds in body. Stachybotrys mould can bring about serious pulmonary disorders. A medical professional and/or local government health authority should be contacted for guidance when there is a concern about health and life safety.