Q&A for How to Acid Wash Concrete

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My new home concrete driveway was poured in early spring, in maybe 45 degree weather. Why is it black and blotchy?

Community Answer

It is still in the curing phase. Usually, when it’s cold like that, the curing process takes longer.

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I have a concrete floor decorated with a colored stain. An animal peed on it and I can't find a cleaner that removes the stain. Is there a cleaner that will bring out the color and shine again?

Community Answer

It is difficult to remove a urine mark once it has soaked in deep, but you can try an enzymatic cleaner made for pet urine. Apply until the concrete is thoroughly soaked, then cover with a tarp until it dries. Once the odor is gone and the urine mark is as light as it's going to get, seal the floor to protect against future spills.

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How long do I need to let the concrete cure before acid washing?

Community Answer

Wait until the concrete is fully cured, or 28 days for most mixes.

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Will acid washing cement reduce the smoothness of the flooring and make it a rougher finish?

Community Answer

Yes. The degree of roughness depending on the acid's strength and how long you leave it on. Use a mild solution and wash if off quickly if you don't want the concrete to get too rough. That said, the concrete does need to be a little rough if you plan to add a sealer.

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Question

I spilled turpentine on our acid washed floor after we had the shiny seal on it and it removed the finish. What can be done to repair it?

Community Answer

If you used a solvent-based sealer, you may be able to apply more over the damaged area, then agitate it with a broom to mix it into the first seal. An epoxy sealer requires sanding and the application of a second layer, and it may be more difficult to make the repaired patch match the rest of the floor.

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What if I want a color on my concrete? Do I add the color before or after the acid wash?

Community Answer

Skip the acid wash completely if you are using an acid-based color stain . If you have already acid washed your concrete, apply a water-based stain once the concrete is dry.

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Will hydrochloric acid damage PVC pipe during cleanup?

Community Answer

HCl will not damage PVC piping. However I would not dump it down a PVC drain to the sewer. Please mix it will sodium bicarbonate until the pH is neutral (around a 7) before discarding.

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Question

I've power washed my concrete patio, but there are still mold stains. Can I use an acid wash to help match the coloration?

Community Answer

A better bet is to soak the concrete with detergent and bleach, let sit for a few days, then rinse while scrubbing with a stiff brush. Try 1 ounce powdered laundry detergent, 1 quart 5% household bleach, and 3 quarts water. (Adding 1 ounce TSP increases effectiveness, but this chemical has serious safety and environmental risks.)

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Question

Will this technique work to sterilize a concrete floor? We had water damage and discovered musty roots growing through tiny cracks in our foundation. We would like to make sure they don't come back, then reseal the concrete.

Community Answer

1 part household bleach and 3 parts water is a more effective disinfectant. You may want to hire someone to check the foundation before you seal it. Even small cracks may need filling to keep out pests and water.

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Can I acid wash a 30 year old shop floor?

Community Answer

Yes, as long as you strip off any sealer first. Note that acid staining (a different process that adds color to your floor) is less likely to work on an old floor. Try a water-based stain instead.

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Question

Can I acid wash colored concrete?

Community Answer

Yes, but I can't predict the result. You can acid wash anything you like. It's just that some you may have some issues when applying it on some surfaces.

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