Prepare bare concrete for coating or staining with Rust-Oleum EPOXYSHIELD Concrete Etch. This citric-acid-based formula is easy and safe to use indoors or out and will open up tiny pores within the concrete to allow for maximum penetration and adhesion. Best solution for water-borne coatings. Environmentally friendly, citric-based formula. Prevents dangerous acids or fumes; will not harm grass or plants. Apply with a plastic watering can and a push broom.