Mortar is a paste for binding bricks and other construction blocks together, and for filling in gaps and spaces. Mortar becomes hard, like cement, once it sets. Mortar sets quickly, and once set, it's hard to clean off using regular supplies. You can use muriatic acid to clean mortar off bricks and other surfaces. However, make sure to handle muriatic acid with extreme care, as it can damage almost anything it touches.
Things You'll Need
1 gallon water
1 cup muriatic acid
Still bristled masonry brush
Use a plastic drop cloth to cover surrounding items and surfaces to protect them from the acid.
Pour 1 gallon of water into a plastic bucket, then add 1 cup of muriatic acid. Be sure to add the water first and then the acid to ensure that the acid does not burn through the bucket.
Apply water to the mortar that needs to be cleaned using a damp rag; you want to make sure the mortar is damp before applying the mixture. If the area you're cleaning is large, you may also pour the mixture into a plastic spray bottle and spray the area; however, after a few applications, the acid will burn through the plastic, so have extra spray bottles nearby.
Saturate the rag with the mixture and apply the mixture to the mortar liberally. Allow the mixture to soak on the mortar for about two to three minutes.
Use a stiff bristled masonry brush to scrub off the mixture while rinsing with a garden hose. Continue to rinse the area thoroughly and scrub until the mortar is cleaned.
Wear heavy duty work gloves, long sleeves and protective eyewear when working with muriatic acid.