Lichen/ algae organic growth
There many Types of Lichen and can be present in different colours including grey, orange, red, black, yellow or green. Lichens normally form a crust like surface on the surface.
Algae is normally green in colour although can also be black, red, orange or yellow and forms a matt- like film on the surface or streaks down the surface.
Fungi colours can be black, orange, yellow, red or brown and form as a film or spots.
Cause
Generally occurs in conditions where the surface remains damp and to the northerly and westerly elevations.
Textured surfaces are more prone to holding moisture than smooth surfaces
When present on exterior surfaces, it is most likely to be associated with moisture in the substrate and lack of air flow; close proximity to trees can also be the cause.
Lichen on interior walls is due to heavy condensation and the lack of air flow
For exterior walls power wash to remove all mould / algae back to a clean surface. It may be necessary to pressure wash or light sand blasting.
Apply two coats of recommended fungicidal wash, allow 24 hours drying between coats and allow the surface to dry out.
Apply selected manufactures masonry finish in accordance with their recommended instructions.
For interior walls remove by heavy scrubbing and washing with a solution of bleach and or a proprietary fungicidal wash back to a clean surface. Once the surface has dried then apply the selected wall finish strictly in accordance with manufactures instructions.