Removing Stains From Precast Concrete SurfacesDownload this information in a PDF file.
Note: It is recommended that trained professionals be used to perform the required procedures. Appropriate public protection should be maintained at all times.
Lubricating or petroleum oils readily penetrate into concrete surfaces. Remove free oil promptly by soaking it up with paper towels or clean cloths. Cover the spot with dry powdered cement absorbent for a day. Remove and repeat if necessary. If the oil has penetrated the concrete, scrub the area with strong soap, scouring powder, trisodium phosphate or proprietary detergents specially made for removing oil from concrete.
Molten bitumen can be satisfactorily removed because it does not penetrate the concrete. Cool the bitumen with ordinary ice until it is brittle and chip off with a chisel. Scrub the surface with scouring powder to remove the residue and rinse with clear water.
Soak up freshly spilled paint with paper towels or clean cloths. Scrub the stained area with scouring powder and water until no further improvement is noted. Wait 3 days for the paint to harden before removing further. Scrape off any hardened paint. Apply a poultice impregnated with commercial paint remover. Let stand for ½ hour. Scrub the stain gently and wash off with water. Scrub off any remaining residue with scouring powder.
Colour that has penetrated the surface can be washed out with dilute hydrochloric or phosphoric acid.
Commercially available products are available for removing spray paint, felt-tip markings, crayon, chalk and lipstick from concrete surfaces. Follow manufacturer's directions and repeat if necessary - try using other products.
A single product may not remove all substances. Effective cleaning can also be accomplished with waterblasting and sandblasting.
After the graffiti is removed or before a structure is in service, an anti-graffiti sealer coating can be applied to prevent graffiti from entering the pores of the concrete (to facilitate any future removal).
Carefully apply a trichloroethylene poultice after making sure the area is well ventilated. Brush off when dry and repeat if necessary. Then scrub thoroughly with clear water.
Alternately, scour the surface with pumice to remove surface deposits and wash with clear water. Follow this with a poultice of commercial sodium or potassium hypochlorite solution (Janola). Hold poultice firmly against the stain. Resaturate the poultice as necessary.
Some dirt can be removed by scrubbing with detergent and water or with 1 part hydrochloric acid in 20 parts water. Proprietary cleaners can remove dirt with minimal attack of the concrete. Do not use acid on white surfaces.
Steam cleaning, light sandblasting and waterblasting are also effective.