http://www.concretenetwork.com Good surface preparation is key before application of decorative concrete stains. Smiths Green Clean makes the process easier and safer. The bio-degradable gelled acid is noncorrosive so it wont harm vegetation yet is strong enough to clean and lightly texture the concrete to improve stain penetration. Simply apply the gel with a roller to uncoated concrete surfaces, and then allow it to sit for 20 minutes before rinsing with water.