We are gutting a basement bathroom that has had boards and drywall glued to the concrete foundation. We plan on redoing the walls with furring strips, insulation etc but on removing the old boards we are finding a brown powdery substance on the surface of the concrete, in some places in lines and clumps but not all over. It is kind of fibourous looking in nature when clumped together. Touched it with bleached with no reaction and also doesn't look like mold, also brushes off. But don't know what it could be. Maybe a silly question but could it be dirt leaching throught the concrete walls?
Done searches on mold and doesn't seem to apply to this stuff. The house is
38 years old and the old drywall could of been up for years.
Any ideas? Thanks Chris