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Acid etching the garage floor is sometimes the only viable alternative for many DIY home owners when prepping concrete correctly to accept a coating. It isn’t hard to do, but certain safety precautions and steps need to be taken to insure a successful and safe outcome. Potentially dangerous if not done correctly, it can not only damage your concrete, it can cause serious bodily harm as well. So please take the time to learn how to acid etch your garage floor or concrete safely before jumping into your project head first.
Muriatic acid, also known as hydrochloric acid, is the typical acid of choice when etching concrete. It is inexpensive and a dangerous chemical that can damage almost anything it comes in contact with. It will eat through clothes, metal, skin, and creates a noxious vapor that can cause surrounding metals to rust as well as burn the lining in your nose and lungs. You can purchase it from your local home improvement center for less than $10 a gallon at a strength of 31.45%.
Phosphoric acid which is a mineral acid works almost as well and isn’t as dangerous to work with, but it is harder to find and more expensive. It also works at emulsifying oils – something that muriatic acid will not do. Both will remove rust from your concrete.
If you don’t like the idea of working with acid, you can read about some safer alternatives to acid etching here.
Supplies and protective gear for acid etching
- Hose with adjustable spray nozzle
- 5 gallon plastic bucket
- Plastic 2 gallon watering can
- Acid
- Baking soda
- Stir stick – wood paint stick works fine
- Push broom or long handled scrub brush
- Rubber gloves
- Rubber boots
- Splash safety eye goggles
- Approved respirator for working with acid fumes
- pH paper test strips
Acid is generally mixed at a ratio of 3 parts water to 1 part acid for sufficient strength to etch properly. Ideally you want to test the strength needed first before doing the entire floor. You can do this by first mixing a small solution in your watering can starting at a 5:1 ratio. Apply it to a small area of wet concrete. It should begin bubbling and fizzing immediately. If not then you will want to increase the strength accordingly. Sometimes a ratio stronger than 3:1 may be needed for particularly dense concrete or a smooth power troweled floor.
Caution! Always add acid to water, not water to acid. If you pour water into acid it can cause an explosive reaction that can spray you with the mixture and burn your skin!
Before acid etching, make sure the garage floor is cleaned properly of all oil, contaminants, grease, and dirt. Contrary to what many people think, acid will not clean grease and oil spots. In fact, if these areas have not been cleaned and degreased properly, the acid solution will just sit on top and not react with the concrete.
1 – Dampen the concrete:
Use your hose to lightly spray down the concrete in your garage so that the concrete is wet but not puddling water. If you have a large garage floor, you may want to acid etch in sections. Do not let the concrete dry out before or during application of the acid solution.
2 – Apply the acid solution:
Use the 2 gallon plastic watering container to sprinkle the acid solution on the concrete. This will spread the solution evenly without much splashing. Do not just pour it on the concrete. This will create an inconsistent spread of the acid solution and will not provide for a uniform result. The 2 gallon container works well because you can mix 1.5 gallons of water to .5 gallons of acid for a 3:1 ratio. You can use any size you like, however, as long as you mix the ratio of acid to water correctly. 1 gallon of a 3:1 acid solution will cover approximately 50 – 70 square feet of garage floor.
3 – Scrub the acid solution:
Once the solution is applied, lightly scrub it into the concrete with a push broom or long handled scrub brush. This helps to create a uniform etch of the concrete. Let the solution sit for 10 – 15 minutes while it continues to fizz and bubble. Do not let the floor dry out during this process. Add more solution if necessary.
4 – Neutralize:
Mix 1 cup of baking soda to 1 gallon of water in your large 5 gallon bucket and pour it into the now empty watering container. Sprinkle your neutralizing solution over the part of garage floor that was acid etched and let it sit for a minimum of 10 minutes. When time is up, rinse the neutralized solution with your hose into a drain or out the garage (if local water codes allow it). Another method is to use a wet vac and then dispose of the solution according to your local codes.
Check the surface of the concrete at this time. It should feel similar to medium grit sand paper with a uniform texture. If not, you will need to repeat the process again.
5 – Final rinse:
Once the initial neutralizing solution is cleaned up, it is important to thoroughly flush and rinse the remaining solution out of the concrete multiple times. It can leave a white powdery residue (calcium carbonate) on your garage floor once dried if you do not do this. This is a fine white dust that will not allow your coating to adhere properly. Use a high pressure nozzle while thoroughly scrubbing the concrete with your scrub brush. You can introduce a mild solution of Simple Green at this point if you like. Just make sure it is thoroughly rinsed.
Using a pressure washer for this process well also. Do not use a pressure washer to rinse off the initial neutralizing solution however. It can drive any acid solution that had not been neutralized deeper into the concrete and cause problems later.
6 – pH test your rinse water:
After your final rinse, dab a pH test strip like these at Amazon onto the still wet garage floor to check the pH. Anything between 6.0 and 9.0 will work for most coatings with 7.0 (neutral) being ideal. If it’s below 6.0 then the water is indicating that acid residue is still in the pores of the concrete. Rinse some more and repeat the test until you get the results you want.
Further Tips for Acid Etching Concrete
It’s a good idea to cover anything in your garage that you don’t want to get splashed with a plastic drop cloth. Another recommendation is to mix some neutralizing solution up ahead of time and spread it out liberally on your driveway. That way any acid solution that is hosed out will not mildly etch or discolor your driveway. Don’t acid etch the concrete if the temps are below 50 degrees as the acid will not be as effective with the cooler temperatures.
Also, make sure your garage floor has dried thoroughly before applying epoxy coatings. Fans will help. Give it at least two days with warm weather and longer if it’s humid or cooler. Though the surface may be dry, the pores of the concrete can still contain moisture and escape through outgassing when the temperatures rise during the day. This will cause your coating to form bubbles. You can always do a quick moisture test with plastic if you are not sure.
Learning how to acid etch your garage floor isn’t hard, but it’s very important to follow the proper steps. When done correctly, the chances of having your coating fail due to improper preparation of the concrete is reduced significantly.
It seems using the grinder is the better option, if I Understand it right if I use the grinder then I dont need to do the etching is that correct?
Thanks,
Tony
Yes, that is correct.
I acid etched my floor. Used the baking soda to neutralize it, rinsed thoroughly and then power washed it. The next day floor is covered in white dust. What can I do to remove dust?
Hello Tim. The white dust is all the fine concrete that was deteriorated by the acid solution. It settles in the pores of the concrete when the solution is allowed to sit too long and begin to dry on the surface before and/or after being neutralized. It’s important to always keep the concrete very wet when etching. It will require some strong scrubbing and rinsing to get the white powder up. Sometimes re-etching with a milder solution will help to remove the white residue from the pores.
I’m getting ready to etch a garage floor again. The last time I did it, I had a hard time keeping the floor from drying while spraying the solution. The garage I’m about to do is significantly larger than the last one. Any tips on keeping it wet while etching?
Hi Aaron. Just do one half of the floor at a time. Also, you should not be using a sprayer. You do not want to possibly atomize an acid etch solution. Plus, it will not deposit enough solution on the floor. Make sure you wet the floor first and use the watering can method for dispersing the etch solution. That should be enough to keep a good section of the floor wet. If it looks like it’s even coming close to drying a bit, sprinkle some water on it.
Hello! I need to etch and coat a 4” line only. Do you have any suggestions of how to keep the etching with a sharp edge. Is there a tape that will hold up to the muratic acid mixture that I could use to line the edge of the 4” line?
Hi Dan. What is it you are going to apply that requires just a 4″ wide strip?
I need to paint a hatch area next to a handicap stall in a garage on concrete that is very smooth.
I see. Containing an acid etch within a small boundary like that is difficult. The etching solution can still migrate some under the tape. In addition, the tape will not hold the solution back unless you are taping down heavy plastic around the perimeter to prevent the solution from running over the tape. You would be better off using 40 or 60 grit diamond paper sanding block or sanding wheel. That should be able to scuff up the concrete enough for your application.
Hi,
Basement crawl space has no way of etching with lots of water use as there is no drainage, so I washed & scrubbed with pure white vinegar which dried relatively quickly and then I covered the floor with dry B Soda & left it for 2 days to absorb any smells. I then swept it up but now I need to seal the floor to stop future smell & mold. The B. Soda is virtually gone but there may be fine dust from it remaining. Can I paint it with Acrylic sealer now or should I do something prior to sealing?
Thank You
Derek
Hi Derek. We recommend that you use a shop vac to get all that dust up. It will impair how well the acrylic sealer will adhere. Once you do that you can apply the sealer.
I used a 1:4 solution of muriatic acid to etch a new pour of concrete . Three weeks old. Upon applying the solution to the concrete, the concrete turned brown. Can you tell me why and if I can remove the brown stain and how?
Hello Wes. You really should wait a minimum of 28 days before etching concrete. I’m assuming that that solution was 1 part acid to 4 parts water? What you left out was the process you used. Was the concrete damp or wet before the solution was applied? How long was it left on the concrete and did it dry out at all? Was it properly neutralized or was it just rinsed with water? Unfortunately, most stains caused by acid are permanent. Sometimes a mild acid etch (properly done) will bring some of the natural color back. Grinding is the usual method to remove the color change, providing it did not go too deep. What was your goal for etching the concrete to begin with?
I have an issue, we moved into our new home and found that laundry (10×10) attached to garage was a living quarters for cats, also leaks that led us to remove drywall and insulation.
We have tried distilled vinegar for about 1 week on concrete and one of the walls that seems to have no damage.
We have put the room back together with new insulation and drywall but there is still the smell that lingers. Now of the first smell plus the vinegar.
Picked up muriatic acid and I was going to get epoxy as well, after reading comments not sure if I should use acid since there are some copper pipes I can see and the pressure treated 2×4 exposed.
What should I do to get rid of smell. We do want to put tile on the floor.
Some contractors tell me to seal it with epoxy or even coat of killz on the floor.
Too many different directions, I am inclined to do the acid wash but do not want to hurt the existing pipes and structure.
Should I just seal it
Hello Marco. First, we highly recommend that you read our post on eliminating pet urine odors in concrete. Follow the steps and see what you have in terms of odor (if any) afterwards. After that, you can determine better what to do with the floor. Where are these copper pipes at in relation to the concrete floor?
I just got done painting my garage walls. I also pressure washed concrete and could not get off all the over spray paint. Will etching help dissolve a lot of that overspray paint?
Hi Scott. This is a common misconception with acid solutions. Acid etching works by reacting with the minerals in concrete. It will not do much with paint. You will need to scrape, sand, or grind the paint to remove it.
I have a garage floor that has 15 year old epoxy on it. It’s in decent shape but I want to put new epoxy (Rust-Oleum Rock Solid) on it to freshen it up. How should I prepare the floor to ensure good adhesion of new epoxy? Thanks!
Hi Steve. We have an article here that discusses how to recoat old epoxy.
Hi – I see that a minimum amount of time is needed between etching and painting/sealing a concrete garage floor so that it dries, but is there a maximum time? If I etch now and don’t paint/seal until potentially weeks or even a month+ later, is that a problem? It is old concrete. Trying to plan around potentially colder weather. If it makes a difference, am using an eco etch product instead of acid and sealing with a polyeruthane. Thank you!
Hi Sara. Once you etch it is permanent. The concrete does not change back to its original state. The only problem with waiting after etching is that the open pores in the concrete will easily collect dirt and debris and get dirty quickly. It will need to be properly cleaned and scrubbed first when the time comes to apply your coating.
Great, thank you!!
Do i need to degrease if i am using a concrete grinder?
Hi Maggie. Only if your floor is real dirty or greasy. If it’s fairly clean as is, then it’s not necessary.
We sanded the concrete floor to a medium grit sandpaper finish. Do we still need to Acid Etch? We also have pressure washed the floor but there is a tiny bit of fine concrete dust in places. Will this cause problems?
Hi Misha. Did you grind with a proper diamond impregnated concrete grinding tool or did you sand?
Yes we used the diamond impregnated grinder.
OK, good. No you don’t acid etch. Grinding is the preferred method and supersedes acid etching. Also, you should not introduce water to the concrete after dry grinding – especially a pressure washer. It drives water deep into the concrete through the freshly opened pores. Make sure to let the concrete dry for a few days at least before applying a coating or you will get bubbles from water vapor that is still trying to escape. A small bit of concrete dust is fine. We always recommend wiping the surface down with denatured alcohol on a microfiber mop pad if you are worried about dust after clean up.