Things You'll Need
Proper safety gear
Often used to clean outdoor pavements, muriatic acid is extremely corrosive and highly caustic. Made of the same chemical elements as hydrochloric acid, muriatic acid must be used with great caution. But as dangerous as muriatic acid is, it also has its benefits. Concrete and other surfaces that do not accept paint readily can be cleaned with the acid.
Dress in proper clothing and safety gear for the job. Because muriatic acid is a caustic chemical, wear protective gear such as goggles, gloves, long-sleeved shirts, pants and closed-toe shoes. You want to keep as much of your skin protected as possible.
Measure one part muriatic acid to 20 parts water in a plastic bucket. This is the safest and most ideal strength for use in cleaning concrete and other outdoor surfaces. This is a general rule of thumb, so always read the package instructions for a varied mixing method.
Hose down the concrete completely with your garden hose. You want the area to be fully saturated before you begin cleaning. This will also free the concrete of any loose debris.
Apply the muriatic acid solution to the concrete with your scrub brush. Allow the muriatic acid to remain on the concrete for at least 10 minutes after a strong scrubbing. This will allow the chemical compounds to be released into the concrete, making painting or staining more acceptable.
Give the concrete another saturating spray with your hose and remove as much of the acid as possible. Repeat the process as necessary if the desired amount of cleaning has not been reached.
Remember that muriatic acid can be diluted to lesser strengths than the 20-to-1 ratio, which allows it to be used on other surfaces besides concrete and brick.
Never mix muriatic acid with any other chemical. This can result in a dangerous chemical reaction that can have severe consequences.
If using muriatic acid indoors, be sure to have proper ventilation.