Cause Algae are green chlorophyll-containing organisms that obtain their nutrition by photosynthesis. Like mildew, algae will flourish where there is an adequate source of moisture. It grows almost exclusively outdoors. Cement-based products are more prone than other substrates to support algae growth.
Solution
Provide drainage to rid immediate area of excess ground moisture. Locate and correct source of moisture that is saturating vertical surfaces. Remove algae growth with a soft brush and household bleach. Flush area with clean water and allow to dry thoroughly. Remove loose paint to a sound surface. Sand weathered wood to fresh wood.
