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How to clean up mortar stains on brick

A handyman doing repairs left mortar smears on this brick wall. The stains are easy to clean using a common acid. (Beth Dunkleberger)
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My brick house was built in 1921. The bricks are a mixture of brown, various shades of red, beige and black. I had some deteriorating mortar replaced, and the handyman smeared the mortar on the brick. What do I have to do to clean up the mess without harming the brick? I’m worried about color fade and that the cleaning process will damage the brick. What would you do? Beth D., Enid, Okla.

I’ve got great news for you. You’re going to be able to clean the smeared mortar from the brick and make your home look like new. The amount of work it’s going to take will depend on how messy the handyman was. If you just have a light film of mortar haze on the brick, it will take minimal time. If there are clumps of mortar including sand on the brick, that’s going to take more time.

The photo you sent shows just a light haze of mortar, but it also tells me that your home was built using a very durable brick that’s quite hard. This is why your home, after resisting weather for nearly 100 years, still looks in great shape.

Let’s talk about your brick first so you know why the cleaning process I’ll recommend won’t hurt it. Your brick was made from clay that no doubt has high silica content. When this clay was formed into the brick and then put in the kiln, it was transformed into a very durable man-made rock.

The longer the clay is allowed to be in the kiln, and the hotter the temperature, the harder the brick becomes. Some brick becomes so hard it resembles granite cobblestones. A small portion of the main street in Athens, Ohio, is paved with brick and it’s still in remarkable shape after more than 100 years of harsh winter weather. Brick laid on the ground takes the worst beating from the weather, so the brick on your home could possibly last hundreds and hundreds of years as long as there’s always a good roof on your home.

To clean the smeared mortar off your brick, all you need to do is brush away the cobwebs from your high school chemistry class experiments. Brick mortar is an alkaline material. You can dissolve alkaline compounds with acid.

A simple example of this happens to be hard water spots. These white splotches on plumbing faucets and countertops can be quickly cleaned up with regular white vinegar you have in your home. The hard water spots are alkaline and white vinegar is a weak form of acetic acid. Try it and be amazed.

Vinegar is too weak to use on brick mortar. You’ll have to step it up and use hydrochloric acid. Muriatic acid is the common name of this acid when you look for it at a hardware store, building-supply store or home center. This is a toxic acid and quite dangerous straight out of the plastic jug. Be very careful with it and read all the safety instructions before you even think of taking off the cap.

The muriatic acid needs to be diluted before you use it or you can permanently damage the brick. It’s best to start with a 1:10 solution. This means you’ll mix one part acid to 10 parts clean water. Do this in a clean plastic bucket. Do not mix the acid in a metal container.

When you work with muriatic acid, wear your oldest clothes, as well as rubber gloves and goggles — not safety glasses. You do not want muriatic acid on your skin or in your eyes. It will cause serious burns. If you do make a mistake, flush your skin or eyes with water as fast as possible and get medical care right away.

My advice is always the same when you decide to put chemicals on a surface. Do a test first in an out-of-the-way location. You know the brick on your home is all the same, so go to the back or the least-viewed side of your home and test the solution on some brick you rarely see.

It’s always best to dampen the brick you’re going to clean with water before you apply the acid solution. If you just put the acid on dry brick, there is a chance you can burn or damage the brick. Always work in the shade, not the direct sun. Never allow the acid solution to touch glass, window trim, painted surfaces, aluminum windows, etc. Only apply the acid solution to the brick.

Once you’ve determined the solution will not harm the brick, do a second test on just one smeared brick. Spritz some water on this one brick and then carefully apply the acid solution to just the face of one brick using a small brush. You should see the acid start to foam and bubble on the smeared mortar. This is exactly what you want to see. You may have to look closely to see this chemical reaction.

Allow the acid solution to work for about five minutes. After the dwell period, scrub the brick with a stiff scrub brush and rinse with lots of water. Allow the brick to dry and behold the clean brick that looks like the rest. Once the brick is dry, you may still see mortar smears. If so, repeat the process allowing more dwell time.

You may discover you have to clean your entire house, as spot cleaning will remove any dirt, soot, algae, etc. The acid solution will also help make the new mortar look more like the original, as it will wash off the mortar paste from the individual grains of sand.

Tim Carter is a columnist for Tribune Media Services. Contact him through his Web site:

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