PROSOCO Sure Klean® 766 Limestone & Masonry Prewash is a strong, alkaline-based cleaning compound formulated for use with Sure Klean Restoration Cleaner, Limestone & Masonry Afterwash or Limestone Restorer. When used properly, the prewash dissolves and assists in removing heavy carbon encrustations from brick, terra cotta, sandstone, limestone and most other masonry. Cleans the dirtiest masonry surfaces without sandblasting or extensive labor. Ideal for spot treating heavily stained areas, such as horizontal surfaces, under window sills, eaves, etc., where carbon and mildew stains are most severe. Does not damage or alter masonry surface. Easy to apply with brush or roller. Will not damage glass.