Removing red algae from outside walls

[henrylupton]

I live by the coast with a white plastered house. A red growth seems to be common in the area. While powerwashing seems to remove it I wondered if there is a less agressive way or eliminating this staining.

[KARL]

Since your question has remained unanswered for some time now, I will tell you of my experience which may not be completely relevant. I used a proprietary patio cleaner - these things have a fairly strong anti-algal property. B&Q sell the liquid in tins of several litres at a time (I think mine was 2 litres). Among the places I applied it was on a wall which was coated with masonry paint, but I also used it elsewhere, including on concrete surfaces - successfully throughout. Follow the instructions on the container, taking particular note of the requirement for scrubbing - a brush with short stiff bristles (nylon is perfectly OK) is very useful (the type of brush used in bathing is fine, if you have nothing else to go by). You use wry little volume by just going along in small patches at a time, then rinse off generously and the algae will hopefully disappear. Presumably pink algae will be removed just as easily as green ones, but I cannot make any promises about the effects on your surface - experiment on a small out-of-the-way patch. Good luck.