Throw a cup or small bucket of water in several spots on the concrete that will be etched and stained. Observe whether the concrete absorbs the water or repels it. If it repels water, a sealer or curing agent was used on the concrete; it will need to be removed during the cleaning process in order for the concrete to accept any type of stain, even after etching.
Deep Cleaning Concrete
Remove small stains and spots from concrete by scrubbing it with a stiff brush dipped in water and a strong cleaning detergent. For greasy spots on porous concrete, apply a commercial degreaser -- such as concentrated alkaline soap -- directly to the stain and scrub it. For old or stubborn grease stains, create a poultice to draw the grease or oil out of the concrete. Mix a strong solvent, such as lacquer thinner or acetone, with an absorbent material -- sawdust or kitty litter -- and cover the stain with the mixture. Place a layer of plastic over the poultice and allow it to sit on the concrete for one to two days to break down the stain.
Final Cleaning of Concrete
After removing any deep stains, the concrete will need to have any additional blemishes or agents removed. Depending on what has been previously applied to the concrete, this may involve sanding, scraping, grinding or applying a stripping solvent to remove unwanted layers down to the bare concrete. For deeper cleaning, use a stripping agent mixed with water. If sanding or grinding, take care to avoid scarring the concrete with additional marks that will be highlighted by the eventual staining process. Follow up with a power washing or brush scrubbing with detergent and water; rinse thoroughly to remove all soap residue and concrete dust.
Neutralizing concrete is the final step before applying the etching acid. In a large bucket, mix 5 gallons of water with 1 quart of household ammonia -- the non-sudsing variety. Use a clean mop to apply this to the entire concrete floor. The mop does not need to be wrung out; puddles will dry with no adverse effects. Rinse the concrete with clean water at least twice. The object of this last step is to create a pH of between 7 and 13 on the floor surface; this allows for an optimal environment to receive the etching acid, which can prevent the need for a second etching before staining.