Cleaning Cement off Masonry With Muriatic Acid

How to Clean Cement Spills Safely

By
Joe Norton
Joe Norton
Joe Norton is a hardscape expert who designs and builds walls, patios, and walkways. He has owned and run a hardscape business since 2002. His experience includes professionally working as a mason and tile setter in Maine and Hawaii.
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Updated on 07/03/22
Reviewed by
Kelly Bacon
Kelly Bacon
Reviewed by Kelly Bacon

Kelly Bacon is a licensed general contractor with over 40 years of experience in construction, home building and remodeling, and commercial building. He is a member of The Spruce Home Improvement Review Board.

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Fact checked by
Jessica Wrubel
Jessica Wrubel
Fact checked by Jessica Wrubel
Jessica Wrubel has an accomplished background as a writer and copy editor, working for various publications, newspapers and in public libraries assisting with reference, research and special projects. In addition to her journalism experience, she has been educating on health and wellness topics for over 15 years in and outside of the classroom.
Learn more about The Spruce's Editorial Process
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Project Overview
  • Total Time: 20 mins
  • Skill Level: Beginner
  • Estimated Cost: $10

​When building a stone wall or other stone projects, it is almost impossible to avoid getting mortar on the stones where you don't want it. If you try cleaning off the mortar while it is still wet, it just smears on the stones. An easy solution is to let the mortar dry and, at the end of the project, clean the mortar off the wall with muriatic acid. You can apply these same techniques to most masonry projects involving cement products.

Muriatic acid is also called hydrochloric acid, spirits of salt, or acidum salis. You can buy muriatic acid at hardware stores and home centers. The acid must be mixed with water to reduce its strength so it does not damage the stone or other materials. But even when diluted, an acid-water solution must be used very carefully to prevent damage to materials and potential injury. Always use muriatic acid in a safe manner. 

What You'll Need

Equipment / Tools

  • Garden hose
  • Safety goggles
  • Acid-resistant long rubber gloves
  • All-plastic bucket
  • Stiff-bristled plastic brush

Materials

  • Muriatic acid (standard concentration)
  • Household ammonia (as needed)

Instructions

  1. Wet the Stones

    Use a garden hose to fully saturate the stone. Be sure to get any stone that may come in contact with the acid solution. This is a critical step to prevent damage. Applying acid to dry stones can stain them a yellowish-green color.

  2. Dilute the Acid With Water

    Put on safety goggles and long rubber gloves. Fill a clean, all-plastic bucket with 1 gallon of water. Carefully pour 1 cup of muriatic acid into the water.

    Warning

    Always pour acid into water. Never pour water into acid, as this creates a dangerous chemical reaction that can cause the solution to bubble and splash out of the bucket.

  3. Apply the Acid Solution

    Brush the diluted acid solution onto the stone, using a stiff-bristled plastic brush. Allow the solution to sit for a few moments. You know the muriatic acid is working if you can see it bubble as it reacts with the cement.

  4. Scrub the Stones

    Use the brush to scrub the cement from the stone. Work quickly so that the acid does not remain on the stone for an extended period.

  5. Rinse the Stone

    Thoroughly rinse the stone with clean water to remove the acid solution. If there are surrounding materials that may be damaged by the acid, rinse the area with a solution of 1 cup of household ammonia and 1 gallon of water to neutralize the acid.

    If the first application of acid does not remove the cement, repeat the application with a slightly stronger acid solution, such as 1 part acid to 10 parts water.

1:35

Click Play for Muriatic Acid Safety Tips

Tips for Cleaning Stone With Muriatic Acid

It's best to clean the stone as soon as possible after the mortar or other cement-based material has sufficiently cured. Cement becomes more difficult to remove over time. However, make sure the mortar between the stones has cured before you clean the stones. If the mortar is too soft, the acid will eat into that, too.

Do not let the muriatic acid sit too long on the stones. Keep an eye on the cement that you want to keep, and make sure it is not deteriorating. Also, make sure that the stones remain wet so that they do not become stained by the acid.

Article Sources
The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

  1. Muriatic Acid Material Safety Data Sheet. Hasa Inc. 

  2. Chemical Segregation and Storage Table. National Institutes of Health.