Things You'll Need
Liquid dish detergent
Concrete stain is used to color a surface so it resembles brick, stone or marble. While it is designed to last for years after the initial application, the concrete can be made white again with diligence and the proper materials. Bleach is commonly used to whiten concrete and is very effective at doing so if the initial stain is removed beforehand. Bleaching stained concrete white prepares it for any additional coloring treatments that you may wish to apply in the future.
Wash the concrete with warm water and several drops of liquid dish detergent to remove any debris. Pressure-wash the concrete for best results if the concrete is outside. Pressure washing is normally too messy to clean up on indoor surfaces. Allow the concrete to dry before continuing.
Apply stripper to the concrete with a mop and allow it to set for several minutes. Follow all instructions on the container for best results. Scrub the concrete with a scrub brush to further embed the stripper into the stain. Wear rubber gloves and long-sleeved clothing to protect against skin exposure because stripping compounds are corrosive.
Scrape at any stubborn stain left on the concrete with a scraper to get underneath it and assist the stripper with its removal. Bleach helps whiten the concrete, but is generally ineffective in removing the stain itself.
Clean up the stripper and paint combination with a mop and thoroughly rinse the concrete to remove any remaining chemicals. The concrete should be back to its normal color once it dries. Reapply more stripper and rinse again if the concrete is still colored.
Spray a mixture of hot water and oxygen bleach onto the concrete. Follow the mixing instructions on the oxygen bleach for best results. The oxygen bleach helps whiten the concrete and is not as toxic as chlorine bleach.
Run a scrubbing machine over the oxygen bleach solution after it sets into the concrete to further cleanse and whiten it. Once the concrete dries, it should be significantly whitened. Apply another layer of oxygen bleach and scrub it once more if necessary. Rinse the concrete once you are finished to remove any remaining bleach.
Wear safety gloves and goggles when working with bleach because it is corrosive to the skin.