3f2c04aa_ick___Cleaning___Stain_Removal__Description
[Stain] Timber stains [Cause] Timber stains usually arise from water spreading tannin or resin stains on the wall, particularly from hardwoods. [Removal] Normally timber stains will be removed by scrubbing with a solution of 20-40 grams oxalic acid per litre of hot water. Neutralise the wall after this treatment. [Description] 
The stains are usually brown or grey and are present on both bricks and mortar.
Brick | Cleaning | Stain Removal
Description