Removes grout and mortar smears, mineral deposits and rust stains. This industrial strength concentrated acid based cleaner is specially formulated to etch grout to bond with Modern Stone's Stain Sealer. Use on acid-resistant tile, stone or masonry surfaces. Not for use on natural stone surfaces such as flagstone, marble, travertine, limestone or any other acid sensitive surface. A pre-test for resistance should be performed prior to use.