Cleaning Cement off Masonry With Muriatic Acid

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  • 01 of 06

    Cleaning Patios, Stone Walls, Etc. With Muriatic Acid


    How to clean cement spills effectively is a problem that the DIYer often encounters. Cement products can be messy. Whether you are using concrete or mortar, building a stone wall, patio, or undertaking some other project, there is a good chance that you will make a mess.

    But do not worry, there are ways to clean stray cement off your masonry structure. In this article, we will zero in on one of them, using as an example how to clean dripped cement off a stone wall. You can apply these same techniques to most masonry projects involving cement products.

    To clean cement off a stone wall, we will be using a magical potion. Well, it will seem magical, anyway, to someone who has struggled for years with the messiness of cement. It is called muriatic acid. It will clean cement off stone without damaging the stone (if used properly), even after it has dried.

    But a word of caution is in order, first. Muriatic acid is a handy cleaning option, but it is also dangerous. Read my article on how to use muriatic acid safely. Now that I have frightened the bejeezus out of you regarding this product, let's do some cleaning with muriatic acid.

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  • 02 of 06

    Wet the Stones Before Cleaning Mortar off Them


    When building a stone wall, it is almost impossible to avoid getting mortar on the stones. If you try cleaning mortar off 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.

    The first step is to get the wall wet. Never apply muriatic acid to dry stones. If the stones are dry, the acid can stain them, turning them a yellowish-green color. Make sure the stones that you will be cleaning mortar off are completely soaked before you apply muriatic acid.

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  • 03 of 06

    Dilute Muriatic Acid With Water

    Dilute the muriatic acid with water to lessen its strength. You want to use only enough to remove the cement from the stones. Any more than that runs the risk of damaging them.

    This is important. The order in which you mix water and muriatic acid is important; these steps are not interchangeable. 

    Put some clean water in a five gallon bucket. I usually fill up about a quarter of a bucket. Then, carefully pour in muriatic acid. Start with a small amount of muriatic acid and move on to the next step. If you need more muriatic acid, carefully pour a little more into your bucket.

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  • 04 of 06

    Let the Muriatic Acid Bubble

    You know the muriatic acid is working if you can see it bubble, which means that it is eating the cement off the stones. Allow the muriatic acid to stay on the stones for a few moments and do their thing before you move on to the next step.


    • Make sure the stones are soaked with water before applying the muriatic acid.
    • Make sure the mortar between the stones is cured. If it 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. Make sure that the stones remain wet so that they do not become stained by the acid.
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  • 05 of 06

    Scrub the Stonework

    After the diluted muriatic acid has been allowed to sit, use a stiff bristled brush to scrub the areas of the stonework that are stained with mortar.

    Between the muriatic acid and the agitation by the scrub brush, the cement should come right off. If needed, you can apply more muriatic acid and continue using the brush until the entire surface is clean.

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  • 06 of 06

    Rinse off Muriatic Acid (Repeat If Necessary)

    As soon as you are done scrubbing, rinse off all of the muriatic acid. Don't let it stay on there any longer than is absolutely necessary. Muriatic acid can stain stones, giving them a greenish or yellowish tint if not rinsed off properly.

    There, your stone wall (or patio or outdoor steps or whatever you're building) should now be completely clean. If not, keep going through the process until it's clean.

    Now, rinse everything off and put the cap back on the muriatic acid and store it someplace safe.