Mould or mildew is the formation of black, grey or brown spots or areas on the surface of paint or caulk.

• Warm, moist, humid conditions (bathrooms, kitchens, laundry rooms)
• Poor ventilation for example bathroom walls not drying after the shower is used.
• Low quality water-based paint
• Failure to prime bare wood before painting
• Painting over a surface from which mildew has not been completely removed.

• First test for mildew by applying a few drops of bleach to the area; if it can be bleached away, it is probably mildew.
• Remove all mildew from the surface by scrubbing with a household bleach solution (1 part bleach, 3 parts water). Be sure to observe safety precautions - wear rubber gloves and eye protection. Rinse thoroughly.
• To protect against further mildew, use an ultra premium quality acrylic paint. These paints tend to have more mildewcide than do lower quality paints and will resist the formation of mildew.
• Clean the surface in future as needed with a bleach or detergent solution. Consider installing exhaust fans or improve ventilation in high moisture areas.