If water beads up on the surface, the acid wash may not work correctly. [3] X Research source Degreasing should solve this problem. Trisodium phosphate (TSP) cleaners are not recommended. Any residue left behind can react violently with the acid to release dangerous gas. [4] X Research source
Sulfamic acid is the safest to handle, and recommended for non-professionals. Phosphoric acid creates less fumes. Use it in rooms that contain stainless steel or other acid-vulnerable metals. It’s also a good choice if you’re just cleaning off mineral deposits. Muriatic acid (hydrochloric acid) is the most dangerous option and produces strong fumes. Recommended only for professionals working outdoors.
Keep water nearby to wash spills from skin or clothing. Showers and an eye wash station are ideal. Keep baking soda or garden lime nearby to neutralize spills on the ground. [8] X Research source
Sulfamic acid: 1 pound powder or crystals per 1 gallon hot water (120 grams per 1 L water). [11] X Research source Phosphoric acid: dilute to 20–40%. [12] X Research source Muriatic acid: mix 3 to 4 parts water with 1 part acid, or follow label instructions for a 10% concentration (15% for hard, smooth concrete). These solutions are for etching the concrete. If you’re just removing mineral deposits (efflorescence), use a much weaker mix (10:1 or 16:1 for muriatic acid). [13] X Research source
The concrete must stay wet the whole time. Divide large areas into sections or hose periodically to prevent it drying out. Protect asphalt, drywall, and tarmac with a plastic drop cloth or other physical barrier. [15] X Research source
Sulfamic acid: 1 gallon treats 300 ft. 2 concrete (1 liter per 28 m2). [17] X Research source Phosphoric acid: 1 gallon treats 500–2500 ft. 2 (3. 8 L per 45–250 m2) when removing mineral deposits. [18] X Research source Muriatic acid: 1 gallon treats 45 ft. 2 (4. 5 L per 5 m2). [19] X Research source
Make sure the floor and surrounding objects don’t dry out while you’re applying acid. You may need to hose them down frequently.
At this point, etched concrete should have a uniform texture like medium-grit sandpaper. If the concrete is smoother than this, or if there are still white mineral deposits, apply the acid a second time.
Use a hose to rinse the acid rather than a pressure washer. These can drive acid deep into the concrete. [25] X Research source To be safe, test the final rinse water with a pH test strip. If it is below 6. 0, there is too much acid and the floor needs more rinsing. (Less commonly, a result above 9. 0 means you’ve added too much basic neutralizer. )[26] X Research source
If you do not have plans for the rest of the pure acid, you may want to dispose of it the same way. Acid left in storage can be a serious hazard due to corrosive fumes and the risk of spills.
