The most effective way to clean dirt and stains from concrete without damaging its surface is power washing. Most power-washing equipment is simple to use and cleaning procedures are pretty straightforward. By using the right equipment, water temperature, and cleaning chemicals, contractors can clean virtually all dirt and stains from concrete.
A power washer with a pressure rating of at least 3000 psi and a flow rate of at least 4 gallons per minute provides the most effective cleaning. For faster cleaning of large flatwork areas, wheel-mounted power washers that resemble a lawn mower are available. Cold-water power washers are cheaper, lighter, and simpler to use than hot-water units, but hot water cleans faster than cold water and is better at removing oil and grease stains.
Although water alone can remove dirt from concrete, cleaning chemicals may be needed to remove specific stains, such as oil and grease, rust, and graffiti. Many contractors recommend spraying the stain with the recommended chemical and letting it sit for about 15 minutes before power washing the area.