How to Acid Wash a Concrete Floor

Clear everything off the surface you are going to acid wash. This includes any debris, it's a good idea vacuum the concrete off if possible, at the very least take a stiff broom to it.

Decide how you are going to contain the water. If you are acid etching an interior floor, you may wish to create damns around the entrances. For a garage, usually just washing it out the entrance works well.

Protect the surroundings. Water can seep up into walls, so if you have drywall all the way to the floor you'll need to be extra cautious. If the concrete you are acid washing is adjacent to asphalt or tarmac, you'll need to make sure no active acid hits that or it will discolor the surface.

Make sure you have all the appropriate safety equipment. At the very least you will need large rubber boots so you can walk across the floor once it has acid on it and acid-proof rubber gloves, preferably ones that come up to your elbows. If you are sensitive to smells I would highly recommend using a face mask with an organic filter. This is particularly important for interior work.

Mix the acid into the water, right in the two gallon plastic watering can, starting with a ratio of one part muriatic acid to 4 parts water. You can increase the strength if you need to up to one in two. A typical strength for acid etching is one to three. No matter what your ratio remember to always pour the acid into the water, NEVER the other way around.

Wet the entire surface to be acid etched. There should be no standing pools of water, but the whole surface should be damp. This insures an even etch.

Use the watering can to spread the water and acid mixture evenly over the surface. It should bubble up yellow at this time, if no bubbles appear, it's likely that the surface you are working on is sealed. That will need to be removed by a mechanical means (grinding, shot-blasting, etc) before the avid wash will be successful.

Scrub the surface throughly. For a small surface you can use a rough sponge, for larger surfaces a floor machine works best. You can also use a stiff-bristled broom to move the acid around and make sure it gets everywhere.

Once the bubbles have stopped (this takes anywhere from 2 to 15 minutes) now it's time to neutralize. I like just dumping several gallon jugs of ammonia over the floor, but you can also mix up baking soda and water.

Rinse the whole surface off. Make sure no debris is left behind.

Wait for the floor to dry before applying any coating to it. Depending on the climate and weather, this could take anywhere from hours to days. Going over it with a blowtorch or leaf blower will speed the process up.