Do not take the risk that overcoating will solve the stain problem. Treat the areas before the application of texture systems. Do not use hydrochloric acid to remove these stains, as it may turn them black and make them more difficult to remove. Try oxalic acid or hypochlorite type bleaching agents, caustic soda or a poultice of one of these agents for very bad staining. Oxalic acid is corrosive and poisonous.
Bleaches are poisonous and oxidising agents.
Avoid ingestion and contact with the skin or coloured or organic material. Wood Stains Certain types of wood, hardboard, or paper may produce brownish stains. The wood need not contact the surface, eg. if rain water drips from timber overheads. The information presented is offered as a result of the manufacturer's experience and as such is not to be taken as an offer and does not imply any warranty or guarantee as to the completeness or accuracy of the descriptions or statements contained herein.