Painting Concrete, Muriatic Acid Safety

7 Materials
4 Hours

This summer we began to make a concrete porch look like it's paved with green marble flag stones with brick trim. We are using concrete stains, watered down primers, and chalk paints marbelized together and it's looking pretty good so far!

Transforming old concrete is a lot of fun, but also a little bit scary. It's one thing to do a nice paint job, but also very important that your work doesn't fade or disappear from wear and tear. We wanted our colors to soak deeply into the concrete and be sealed so that they would last a long time.

Before. See the water spots on the left? This is what a corner of the porch looked like before we gave it a deep cleaning. This concrete is circa 1960 and not very porous. We poured water in a few places and timed how long it took to absorb to see how well it might accept stains.

So that all this design work would soak into the concrete, we decided to first wash the porch with diluted muriatic acid. We are safety nerds so we recommend hiring a professional for the acid step. We worked up a safety plan and did the acid wash ourselves.

We used a low-fume muriatic acid, but even this product has to be used with a lot of planning and caution. For instance, you will have to dispose of diluted acid in an area that will not destroy plants. We chose an area where we need to get rid of poison ivy.

Also, we gathered some long-handled brushes like this old mop and barbecue scraper. Long handles are key. Even if you wear chemical gloves, you don't want muriatic acid to get on your clothing.

We planned to use small batches of the acid and work on small sections of the porch each time. There is no water or hose at our job site. We had to truck the water in, in gallon jugs.

We prepared a plain water rinse bucket first, then a neutralizing rinse with baking soda and water. Then we put on a LOT of safety gear (we are not afraid to look like nerds). We've used masks to protect our lungs, a shield to protect our faces, gloves for our hands, and …

… rubber boots! Wearing fleeced lined boots in August is nerdy but safe.

We turned up the cuffs of our gloves to lessen the chance of drips reaching our arms. We poured the acid slowly, but even so, it splashed a little bit. With so many safety precautions, no harm was done.

Wow! The diluted acid fumes and fizzes as soon as it hits the concrete! And look at the dirt that accumulates in the pan after just a small area is scrubbed. By working in small batches, we could start fresh when we moved to another section of the porch.

The acid sat for about 5 minutes before we poured on the neutralizing mix made with baking soda and water.

Then came lots and lots of plain water and much more sweeping. If you have a water hose available, this part may be easier for you. We swept everything into a safe zone where no plants are growing. Do the same if you are blasting the rinse water with a hose.

We used an industrial fan to help dry the porch quickly, and just look how clean that concrete is now! We don't mind some marks and light stains as those will add realism to the faux marble and bricks.

After. Much cleaner, and when we did the water test again, it soaked in much faster. Do you have any tips to share for preparing and staining concrete? We'd like to see your tips below. Our blog post with more photos and steps is here.

Later this month, the fun begins! We'll be chalking in more designs using rulers and then use our stains to create coral bricks and green marble effects. The chalk lines will be washed away later. We'll be posting that progress soon! -- Stephie

Resources for this project:

Muriatic Acid, Low Fume - item number B002GD50HC
Safety Works SWX00320 Multi-Purpose Respirator Half-Mask Niosh Ov/AG/P
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Stephie McCarthy
Want more details about this and other DIY projects? Check out my blog post!

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4 of 6 comments
  • Nadja Stevens Nadja Stevens on May 25, 2020

    OMG Stephie where were these instructions 30 years ago???!!!

    I was told that muriatic acid would kill weeds and anthills on our patio

    made from paver stones...

    so an uncle, who worked in cement,

    gave me a 5 gallon pail of it and told me to pour it between the pavers.

    He didn't tell me that the acid would literally eat the concrete pavers

    or that it stunk to high heaven and killed the lungs!!

    No health and safety instructions, no rinsing it, no neutralizing it!!

    But I survived AND so did the weeds and the ants!!!


    • Stephie McCarthy Stephie McCarthy on May 25, 2020

      Oh gosh, what an experience! Well, now days I'm using white vinegar. I did a concrete floor inside in my green marble floor post and the vinegar worked great. Now I have to figure out what to do with the rest of the gallon of muriatic acid … I definitely won't try it on weeds. Vinegar is better there too! lol! -- Stephie.

  • Elizabeth Telles Elizabeth Telles on Jun 10, 2020

    Make sure that at no point in time the acid is mixed with the baking soda as it will explode! I used to work for a pool supplies place where a customer claimed he had done that.