Acid Washing Concrete: How To & Other Things to Know

Acid Washing Concrete: How To & Other Things to Know

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If you need to prepare your concrete so that you can apply a sealer to it, then acid washing is one of the best methods at your disposal. This technique removes a variety of mineral deposits and other substances from the surface of the concrete, therefore getting it ready for a sealant to be applied. Acid washing is not the safest process in the world, so it does need to be done carefully.

Today we are going to teach you all about acid washing concrete, and how to do it, while also answering your most important questions.

How to Acid Wash Concrete

Let’s go through a quick step-by-step tutorial on exactly how to acid wash concrete. If you follow the steps listed below, you shouldn’t have any problems with this process.

Step 1: Prepare the Concrete

You must first prepare the concrete to receive the acid wash. If water is able to bead up on the surface of the concrete, then the acid wash is not going to work properly, and this problem is going to be solved by decreasing the surface. Therefore, you first want to brush and vacuum any and all physical substances from the concrete. If you have any oil stains or other types of grease on the concrete, then you will need to use some kind of concrete degreaser to remove any residue. Just don’t use any trisodium phosphate products, as this will interact with the acid that you apply afterward.

Step 2: Get Your Acid

The next step here is to actually get the acid that you will use to acid wash the concrete. If you are looking for the safest option, sulfamic acid is the number one choice. If you are a professional, working outdoors, and need the strongest possible acid, then you should choose muriatic acid. Just keep in mind that all these acids are fairly dangerous, so you do need to take great care, which brings us to our next point.

Step 3: Prepare Yourself – Safety First

Some of these acids are extremely dangerous and are corrosive, poisonous, and more. Therefore, you need to protect your lungs using a respirator that features an acid-grade filter and has fans that will help to improve ventilation. You will then want to protect your skin with clothing that fits really well, as well as rubber acid-resistant gloves, rubber boots, and goggles that are also vapor-proof. You do not want any of this acid being inhaled, getting in your eyes, or getting on your skin. This is an extremely dangerous process, so you do need to take great care.

Step 4: Mix the Acid

Now is the time when you will add water to the acid, in a plastic bucket or watering can. Keep in mind that plastic is resistant to acid damage, but metal is not, so don’t use a metal bucket. First, you are going to pour water into the bucket, and then slowly add the acid. Exactly how much acid to water you will require is going to depend on the type of acid being used. For instance, if you are using muriatic acid, you will mix one part acid with four parts water. These acids are generally not used in their concentrated forms and must be diluted.

Step 5: Hose Down the Concrete

Before you can start applying the acid, you do want to hose down the concrete so that it is damp, but not extremely wet. You also want to make sure that all surrounding objects, such as walls, brushes, trees, doors, and anything else are also a little wet. Keep in mind that the concrete has to stay wet the whole time while you are applying the acid wash, so you do want to keep wetting it as you go through this process. If you need to protect things like tarmac, drywall, and asphalt, using a plastic drop cloth is recommended.

Step 6: Apply the Acid, Brush, and Let It Sit

You now want to use something like a plastic watering can to apply the acid to the concrete surface, making sure to hold the water can very low to the ground as you pour it, so it doesn’t splash up on you. Always start with the test area just to make sure there are no adverse reactions, and always work in small sections.

If you are using plastic, especially cheap plastic, the acid may cause it to corrode, so you may need to use several watering cans. Keep in mind that in terms of quantity, if you are using muriatic acid, a single gallon of your mixture will treat about 45 square feet, whereas if you are using sulfamic acid, one gallon of your mixture is going to treat about 300 square feet.

You now want to use something like a push broom or a very long masonry brush to spread the acid out on the concrete in an even layer. Again, make sure that the ground and any surrounding objects around your work area do not dry out while you are applying the acid, so make sure to keep hosing them down. Once all of the acid has been applied, you need to allow it to sit so it can etch into the concrete, which is going to take about ten minutes.

Step 7: Rinse, Neutralize, and Rinse Again

Before the acid has a chance to dry, you want to use a long masonry brush or a push broom, along with plenty of water, to scrub the area and remove as much acid as possible. You do not want to leave the acid on the concrete for longer than 10 or 15 minutes at most, as it may cause damage.

However, simply washing acid away is not going to do it, so you do need to neutralize it. Therefore, you need to mix one gallon of water with one cup of baking soda or household ammonia, and then apply it to the acid on the concrete. You want to use your brush or broom to scrub this over the concrete and allow it to sit for at least 10 minutes so that all of the acid is neutralized.

Make sure that you pay close attention to any edges or low spots, as this is where some of the acid will probably pool up. If you see that the concrete is extremely smooth or still has mineral deposits, you will need to repeat this process.

Once you have neutralized the acid, you will then need to rinse the surface several times. You don’t want to leave any liquid on the surface, especially right after the neutralizing process, because you don’t want any mineral deposits left on your concrete.

Therefore, use a brush and water to thoroughly rinse the entirety of the concrete several times. You then want to use a shop vac to pick up any remaining water.

Mistakes to Avoid, Tips & Tricks

Let’s quickly go over some tips and tricks to help make this process as easy and successful as possible:

  • Do not use any kind of metal throughout this process, as the acid will quite literally melt it away.
  • Always make sure to use safety gear that is rated as being acid-proof or at least acid-resistant, because you do not want these substances getting on your skin.
  • When rinsing away the acid, use a hose, not a pressure washer, because high-pressure streams of water may actually push the acid deeper down into the concrete.
  • This is a job that you can do on a slightly rainy day, because the concrete needs to stay wet the whole time anyway, just as long as it’s not pouring.

Acid Washing Concrete: Frequently Asked Questions

Let’s quickly answer your most frequently asked questions about acid washing concrete.

What Is Concrete Acid Washing?

Concrete acid washing is when you use a variety of acids to wash your concrete. The point here is to make your concrete fairly rough and to remove any substances, such as mineral deposits or grease, so that you can then apply a sealant to the concrete, therefore keeping it protected for a long period of time. Those strong acids are going to wash away virtually any unwanted substance on the concrete.

Does Acid Washing Clean Concrete?

Yes, acid washing does clean concrete, and this is after all the whole point of it. The point of acid washing your concrete is to remove mineral deposits and other substances, therefore getting it ready to receive a sealant.

How Long After Pouring Can You Acid Wash Concrete?

Depending on the conditions, you should wait for around three to four weeks after pouring the concrete to acid wash it.

What Are the Pros and Cons of Acid Washing Concrete?

The biggest benefit of acid washing your concrete is that it prepares it to receive a sealant. Sealant is of course ideal for concrete because it helps protect it from moisture and physical damage for long periods of time.

However, if you do not first acid wash the concrete, the sealant won’t properly adhere to it and will cause bigger problems down the line. Acid washing concrete is also one of the only and best ways to remove those white mineral deposits from the surface.

However, a downside to acid washing concrete, besides it being expensive, is that it is also extremely dangerous, both for humans and animals, as well as for plants. Moreover, if you do not acid wash your concrete properly, mainly if you leave it on there for too long, it may damage your concrete and do more harm than good.

What Acid Should You Use When Acid Washing Concrete?

Sulfamic acid and muriatic acid are the two acids of choice for this process.

Are Acid Washing and Acid Staining the Same?

Acid washing is designed to clean the concrete and prepare it to receive a sealant, whereas acid staining is all about changing the appearance of the concrete to make it look better.


As you should be able to tell by now, acid washing concrete is by far the best way to clean your concrete and prepare it to receive a sealer. Never apply any kind of sealant to concrete without first acid washing it because it simply will not accept the sealant.

Also be sure to stay safe, because this process can be quite dangerous, as these acids are very corrosive.