Zero Bull Concrete and Rust Remover is not only the most powerful cleaner of hardened concrete, rust, efflorescence, mold, & mineral stains on hard surfaces, it's also the safest. Stronger than traditional dangerous acids (muriatic, phosphoric, citric), and safe for people, plants, pets, and the planet, and on glass, plastic, rubber, and most metals (avoid aluminum and galvanized metals). Non-fuming, non-corrosive, non-flammable, color safe, and 100% biodegradable in 10 days. The active ingredient is the patented acid replacement technology, Syntech, which has the power of the strongest acids but without any of the dangers. Used by the biggest businesses and governments worldwide for over 17 years.