Use Viper Renew when all other cleaners have failed. It works on the acid side of the pH scale removing soils and stains on grout, tile and stone that have been neglected for years. Viper Renew actually removes a very thin layer of grout, taking with it all hard water deposits, soap scum and efflorescence. The proprietary organic salt in Viper Renew is twice as effective as phosphoric acid at dissolving calcium carbonate, and without the unpleasant fumes. Keep a gallon of Viper Renew on your truck so you'll be prepared for even the most extreme tile and grout cleaning situation.