Mould and Mildew

Common issues for interior surfaces

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.