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How to Prep a Concrete Basement Floor With Muriatic Acid Before Painting

Emrah Oruc
Protective gear is important when working with muriatic acid.

A finished basement adds utility and square footage to your home. Before you paint the concrete floor in that extra den or family room, however, you must make sure the floor is clean and free of moisture. Latex floor paints do an excellent job of sealing the surface of porous concrete to prevent ground moisture from bleeding through. However, the paint will not stick to the concrete unless the surface is perfectly clean and degreased. Muriatic acid is an excellent product for this application. It not only cleans the surface, it etches the concrete so the paint can adhere better.

Step 1

Scrub the floor clean with a degreasing product and a stiff-bristled brush. The recommended water dilution ratio will be marked on the bottle. As an alternative, a solution of liquid dish soap and water is a cheaper option.

Step 2

Mop the floor with plain water and allow the floor to dry.

Step 3

Open all windows in the basement. Wear protective goggles, rubber gloves and a respirator. Turn on the floor fan, pointing it at an open window.

Step 4

Mix 1 part muriatic acid to 4 parts water in a 5-gallon bucket. A 1-gallon jug of muriatic acid is enough to cover approximately 300 square feet of surface area.

Step 5

Apply the solution to the concrete floor and scrub it in with a stiff-bristled brush or broom. Wait several minutes to allow the acid to do its work. Even though you are wearing protective gear, be careful to not splash any in your eyes or on exposed skin. Definitely make sure no children are around.

Step 6

Mop the floor at least twice with plain water. Run the fan if necessary to help dry the floor. When the floor is completely dry, it is ready for paint.


Start in the corner farthest from the exit and work your way backward. This way, you minimize how much you step in the acid.


Never allow children into the room while the acid is being applied. Muriatic acid can burn skin in stronger concentrations. It also releases noxious fumes (it smells like rotten eggs) that should not be inhaled.