Removing Stains from Concrete Floors

Concrete surfaces are easily stained because of their porous nature. While most stains can be removed easily, some stains may leave traces even after cleaning. As on any other surface, spills on concrete should be cleaned up immediately. Removing stains as soon as possible can prevent them from setting deeper into concrete's porous surface.

The first step to eliminating a stain is to identify the stain and choose the appropriate chemicals to clean it. If the stain is unidentifiable, test your cleaning agents in an inconspicuous area to see if they work. Start off with plain water, then test oxidizing bleaches, reducing bleaches, and, finally, acids.

• Rust Stains. If the stain is light, mop the concrete surface with a solution of oxalic acid and water. Wait for a few hours, and scrub the surface with a stiff (non-metal) brush and rinse with clear water. If the stain is heavy, use a poultice of sodium citrate (available in hardware stores) and lukewarm water. Add a little glycerol to make a hard paste with talc. Spread this over the stain and leave for a couple of days.
• Oil Stains. If the oil is freshly spilled, soak it up—do not wipe it—with absorbent paper. Cover the stain with a dry powdered material like hydrated lime or cornmeal. Wait twenty-four hours and sweep it up. Scrub any remaining stain with scouring powder or a strong soap solution. For older stains, cover with flannel soaked in a solution of acetone and amyl acetate and apply a light weight on the flannel to press it down. Rinse the concrete when the cleaning process is complete.
• Grease Stains. First, scrape the grease off of the concrete. Then, scrub the stain with scouring powder, strong soap, or detergent. If the stain remains, make a stiff poultice with a chlorinated solvent and rinse the residue.
• Dirt Stains. Dirt stains are perhaps the easiest to remove from concrete. Most dirt stains can be removed by spraying with plain water or by scrubbing with a soft brush and a weak soap solution. If soap and water don't work, use a combination of water and hydrochloric acid. Also, steam cleaning is generally effective for removing dirt stains. If the dirt is clay, scrape off the hardened bits and scrub the stain with hot water containing sodium orthophosphate.
• Mildew Stains. Mix powdered detergent, sodium orthophosphate, a little commercial sodium hypochlorite solution, and water to make a hard paste. Be careful with the sodium hypochlorite solution because it bleaches colored clothing and may corrode metal. Apply the mixture, wait for a few days, and then scrub the area with a stiff brush. After scrubbing, rinse the concrete with clear water and the job's done.
• Graffiti Stains. There are various cleaners on the market for removing graffiti stains from concrete. Apply a cleaner that contains an alkali, a solvent, and a detergent. After scrubbing the graffiti with a brush, leave the cleaner in place for the time indicated on the manufacturer's label. Rinse thoroughly and avoid skin contact with the cleaner.
• Asphalt Stains. Since this is typically a summertime problem, you can chill the molten asphalt with ice. Then, scrape or chip it off while it is still brittle. Next, scrub the area with abrasive powder and rinse it thoroughly with water. Do not apply solvents to molten asphalt: they will simply help the asphalt penetrate deeper into the concrete.
• Chewing Gum Stains. As with asphalt stains, first freeze the chewing gum with ice or commercial aerosol freezing agents and chip or scrape off as much as possible. Apply carbon disulfide or chloroform alone or in a paste. Steam cleaning is also effective in removing chewing gum that has been pressed into the surface of the concrete.

As you can see, removing stains from concrete is not the tough job it appears to be. These stains can be removed in several minutes with a little effort or within days by soaking.

If you determine that your concrete floor is almost too stained to salvage, it might be time to think about covering the concrete with some other type of flooring. All sorts of ideas can be entertained, but you may want to talk to a flooring professional for some advice on what would work best in your circumstances.