Cleaning Cement off Masonry With Muriatic Acid

How to Clean Cement Spills Safely

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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 cleaning product called "muriatic acid." It will clean cement off stone without damaging the stone if used properly. It can clean cement off stone even after it has been dry for a long time, but the job will go more smoothly if you apply it shortly after the cement has dried.

Muriatic acid is also called "hydrochloric acid," "spirits of salt", and acidum salis. "Muriatic" derives from the Latin word for "brine," which is water with an extremely high salt content. Brine is used in the production of hydrochloric acid. You can buy muriatic acid in most home improvement stores.

But a word of caution is in order, first. Muriatic acid is a handy cleaning option, but it is also dangerous. It is important that you use muriatic acid in a safe manner

Wet the Stones Before Cleaning Mortar off Them

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When building a stone wall, it is almost impossible to avoid getting mortar on the stones where you don't want it. 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.

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 critical for safety: 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. Fill up about a quarter of the bucket. Then, carefully pour in the 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.

Never reverse the order of these steps. If you pour the water into the acid, it can cause a dangerous chemical reaction: The acid can bubble uncontrollably up out of the container and get onto your body, resulting in a burn. 

Let the Muriatic Acid Bubble

But a little bubbling is normal once you apply the mixture to the cement spill. In fact, you know the muriatic acid is working if you can see it bubble at this time: It 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 its thing before you move on to the next step.

Notes

  • 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.

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.

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.

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.

Rinse everything off and put the cap back on the muriatic acid and store it someplace safe.