Use muriatic acid or another acid etching material such as Klean Strip Green Muriatic Acid, a safer muriatic acid or Hydro-Etch 1000 which is a modified phosphoric acid which is not as harmful as traditional muriatic acids. Muriactic acid is one of the most dangerous chemicals you can buy for home use and it can damage nearly everything it touches. We really like the Hydro-Etch 1000 product since in most cases it does just as good of a job as muriatic acid but with less danger. It is also an excellent choice when you are looking to remove efflorescence from concrete and masonry substrates.
Acid Etching Process:
Remove all furniture, equipment and objects from the concrete floor you are going to be etching, sweep up or shop vacuum any dust and dirt.
Remove all oils and greases prior to etching, this can be done by using a degreaser, laundry detergent or Dawn concentrated dish soap.
Hose down the entire area you are going to be etching. Spread the water and make sure it is not pooling or puddling, the concrete should remain this wet throughout the acid etching process.
The usual dilution ratio is 3 to 4 parts water to 1 part acid. Do not use a metal container to mix the acid and water. Important: Always pour acid into water, never pour water into acid since the acid can splash back into your face and lead to injury. During the mixing stage wear long sleeves, gloves, eye protection and a face mask to protect against fumes.
After the acid is mixed with water test in a small area to make sure the ratio is accurate, you will be able to tell since the concrete will begin to bubble and react. If you dont see bubbles when the acid first comes into contact with the concrete the mixture is not strong enough.
It is easiest to use a sprayer or watering can to apply the mixed acid to the floor. After spraying acid on the floor you can use a squeegee or floor machine to spread the acid mixture. Remember that the floor needs to stay wet throughout the entire acid etching process. Do not let the acid dry on the floor, if you notice that it is starting to dry you will need to hose down the areas.
After the acid has been applied wait about 2-15 minutes for the floor to stop bubbling. Throughout this process the acid is reacting with the floor, opening up the pores of the concrete preparing it to accept a sealer. If there are spots where the acid is not reacting with the concrete there could be residual oil or grease left on the floor and you may need to use a floor grinder to prepare the floor in these areas.
After the 2-15 minutes rinse off the acid from the floor. The next step is to neutralize the surface and reduce the pH of the concrete. You can neutralize the concrete using 1 cup baking soda dissolved in 1 cup water or 4 ounces of household ammonia mixed into 1 gallon of water. Let the neutralizing solution sit for a minimum of 10 minutes. You can then rinse off the neutralizing solution and drain it or shop vacuum it up.
The concrete should now have a cleaner, brighter appearance and it should have the texture of medium grit sandpaper. Rinse the concrete twice and suck up the excess with a shop vacuum. If the concrete is not rinsed enough a white powdery residue will be left on the floor when it dries. This can be removed by rinsing the concrete again.
Helpful Tips:
- Wear protective clothing such as safety googles, gloves, long sleeves and close toe shoes.
- Do not breathe fumes, and use a face mask respirator
- ALWAYS POUR ACID INTO WATER, NOT water into acid.
- Effective pH levels prior to applying a sealer or coating are 6.0-9.0. If the range is below 6.0 there may still be acid residue in the pores of the concrete.
- Use a plastic drop cloth to protect anything you don’t want to get splashed.
- Don’t acid etch in weather below 50 degrees F.
- After etching make sure the floor has dried out before applying a concrete sealer or coating.
The post is based on a very informative article on wikiHow.com titled, How to Acid Etch Concrete.