Superior Pro Grout Epoxy has an exceptionally high resistance to many acids, alkalis, solvents and household stains. It can be used with a mortar as thin as 1/16" to 1/8" after tiles have been properly set. This grout adhesive is also nonflammable, easy to work with and is able to be cleaned with water before it is set. Pro Grout Epoxy and Adhesive Part C in Charcoal is not affected by prolonged contact with water, but it does not form a waterproof surface. If a waterproof membrane is desired, use Merkrete Hydro Guard 1 or Hydro Guard 2000.