The appearance of mildew depends on various conditions, which are:
Continuously high humidity. As the humidity increases, mildew growth becomes more rapid.
High average temperature. Optimum temperature for mildew growth is 20-30 degrees celcius
Poor ventilation. Still air increases mildew growth.
Composition of surface. Mildew will grow on any surface that provides a nutrient, even dirt.
Light colours of paint film. Colours that do not absorb the sun’s heat provide a surface for mildew growth. Dark colours become hot and discourage mildew growth.
Solution: Wash mildewed areas with a solution of one part household bleach and three parts water. This will destroy mildew and bleach stains caused by mildew growth. Apply solution by brush or a garden sprayer apparatus. Heavy mildew may require additional applications, and scrubbing may be required. Flush area with clean water to remove bleach solution. Allow to dry thoroughly.
Follow label cautions when using bleach solution.