Remove any furniture or other items. The area you want to stain must be clean and free of loose paint, dirt and dust, or any other debris. You need access to the entire surface. Use a wire brush and a solution of trisodium phosphate (TSP) and water to scrub the surface clean and remove any foreign matter on the concrete.
Always wear protective clothing when working with TSP. Follow manufacturer’s instructions carefully.
In regions where phosphate use is restricted, use phosphate-free trisodium phosphate (TSP-PF).
If the concrete surface is painted or sealed, you will need to strip off the finish by scraping, sanding or using a chemical stripping agent. Most chemical strippers need to be mixed with water, so check the manufacturer's directions before applying. Using a clean rag, apply the solution evenly over the surface. Let it soak in for 20 to 30 minutes then use a plastic paint scraper, rag or sponge to wipe off the old finish. Once you've removed the old finish from the surface, use a clean rag to wipe it down so that the surface is completely bare. Let it dry. Afterwards, spray the concrete with a pressure washer or hard spray from a hose, and then mop. Allow the concrete to dry, and then thoroughly sweep the entire surface with a broom for good measure.
Remove any oil or grease on the concrete with a degreaser. Apply the degreaser and scrub the stain with a stiff-bristle brush, and then wipe with clean rags. Once you’ve finished cleaning, make any needed repairs to the floor. Fix any cracks or holes in the concrete with a concrete patch or a hydraulic cement. Follow the manufacturer’s directions when applying the concrete patch or hydraulic cement.