How to Clean an Older Concrete Slab Before Applying Acid Stain

I want to acid stain an existing, older concrete slab. What’s the best way to clean the concrete so the stain will take? -David

Hi David,

Cleaning an old concrete slab so it will take an acid stain can be very difficult, but it is possible. The main thing is to NOT use any kind of acid wash or etching solution (including muriatic acid) to clean the slab. The stain will not take at all if you use acid as a cleaner.

A solution of TSP (trisodium phosphate) and a lot of elbow grease with a scrub brush would be your best bet. Using a scrub brush with a long handle makes cleaning much easier. Another option would be to use a pressure washer to clean the concrete slab. For grease stains on concrete, try scrubbing the stain with lacquer thinner or mineral spirits.

Even with your best efforts, you may wind up with patches on a concrete slab that simply won’t take an acid stain due to low lime content in the concrete (lime is what causes a chemical reaction with the acid stain). In those cases, you may have to resort to applying a faux finish to the spots to try and match the acid stain in the surrounding areas.

Good luck with your project,

Danny

Further Information

3 COMMENTS

  1. Thank you Danny so much for all the excellent advice and know how you offer to all of us. I am 60years old and my daughter is 30 and we are trying to redo all of the floors in our home. We recently purchased this home, and there is severe animal stains and odors we have to get rid of. We are on a very tight budget, and have removed almost all of the carpeting in the home. We have 2 stories, and bottom floor is cement slab, extremely uneven, cracked and a mess. We really want to stain the downstairs cement floors, but are doubtful we have strength or capability to complete. Please any other advice would be extremely greatful. Help us please. Thank you; Zellann and Courtney.

  2. This answer was just what I was looking for as we’re trying to figure out why our 20-year old concrete patio won’t take the acid stain in some areas. This explains it–we used an acid cleaner from the start. So now my question is,now that we see we made a mistake during prep, how do/can we correct it? Is there maybe a way to add lime back to the old concrete, so that the stain will take?

    Thanks!

    Windy

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