A mild organic acid cleaning compound, neutralises and brightens surfaces that have been prewashed with 766 Limestone and Masonry Prewash. When used properly, this two part cleaning system removes heavy carbon dirt and other atmospheric stains from porous limestone, concrete and most other porous masonry surfaces. 766 Limestone and Masonry Prewash and Limestone and Masonry Afterwash will not damage most masonry surfaces.