Wood Stain Algae
Staining
Cause
Organic growths as a result of the timber having been exposed to rain water with the moisture content in the wood remaining high. Most prevalent when shaded from direct sun light.
Remedy
Once the staining has occurred, thorough sanding down is needed to remove all the surface contaminates back to bare timber followed by washing down with a fungicidal solution and allowed to dry, followed by recoating with the selected wood finish in accordance with manufacturers instructions.
Note: If it has not been possible to remove all the discolouration then a darker shade of finishing colour will have to be considered.
Alternatively an opaque microporous coating could be considered.