Muriatic acid is a strong acid cleaner used on masonry surfaces to clean stains. With proper use, it removes stains when other cleaners fail. If the acid comes in contact with skin, wash it away with large amounts of water.
Wear proper protection
Muriatic acid is highly corrosive. It can burn your skin and cause choking, sinus irritation or frostbite, according to HowStuffWorks. Wear a respirator designed for use with hydrochloric acid, gloves, goggles or a face shield and a long-sleeved shirt with long pants or a chemical resistant suit.
Mix the solution
Dilute the acid with water at a 1 to 4 ratio. Always add the acid to the water to help prevent acid splashing out of the mixing container. Pour the acid into the water slowly. Mix well.
Apply the solution to the surface
Use a garden sprayer or paint brush to apply the solution to the stain. You should see a chemical reaction as soon as you apply the muriatic acid. The solution begins to bubble, and it lifts and removes the stain. Leave it in place for 20 minutes.
Rinse the surface
Use a garden hose and sprayer to rinse away the acid once the stain is gone. Use ample amounts of water to dilute the acid as it washes away.