Re: Pressure Washer - Proper Procedure
The leaves and tree debris probably had a of of tannic acid in them (most likely the cause of the dark stain) which in time will dissolve the limestone in the concrete. The stain probably just was hiding the aggregate or it was deteriorated anyway, so the pressure washer at worst just sped up the removal of the softened surface. An alkaline cleaner would possibly neutralize the acid some, but not enough to save the softened concrete. Another cause of staining is iron and sulfur in the water, common in a lot of wells. If you water the lawn from a well that has a lot of iron in it, it will also result in staining. This was a bad problem when I lived in FL, and the only solution I saw while there to prevent the deterioration was sealing the concrete with a waterproof sealer. Bleach helped removing black mildew stains, but did little for the iron/acid staining. Possibly one of the construction pros that work with masonry can give better advice.
Originally Posted by Phil3
Practicing at practical wood working