How to Remove Stains from Brick and Concrete
Efflorescence
Efflorescence is caused when moisture within the brick or concrete dissolves the salt in the mix. The efflorescence leaches out and causes a white stain on the outside of the masonry that can be removed with water and a brush. If some residue of the stain still remains, use a 1 to 10 muriatic solution to remove the efflorescence from dark brick or concrete. For light brick a weaker 1 to 15 solution should be used.
Brown Stain
A brown stain on brick is caused by manganese in the mix. Although manganese is purposely added to darken the brick color, it can be removed if it is overly staining the bricks surface. Many manufacturer’s make products to remove manganese, take a look at your local home and garden store.
Moss
Moss can be removed from brick and concrete by using ammonium sulfamate, which can be found at most home improvement and gardening stores. Just apply according to the manufacturer’s instructions to kill and remove any moss.
Smoke
To remove a smoke stain from concrete or brick, use a mildly abrasive bathroom or kitchen cleanser. Be sure to rinse thoroughly and do a spot check on concrete before applying.
Green Stain
Found in brick, a green stain is caused by vanadium salts in the mix. To remove first wash off as much residue as possible with clean water and a towel. Then use a 1 to 10 muriatic acid solution to remove the stain from dark brick or a weaker 1 to 15 muriatic acid solution for lighter brick. You should then apply a solution of 8 ounces of sodium hydroxide diluted into 1 gallon of water to the face of the brick. Allow the mixture to sit for a few days, and then remove it with water.
Oil, Grease, and Tar
Oil and grease can be removed from brick or concrete with a degreaser that can be found in automotive and home improvement stores. Spray degreasers are the easiest for walls; they only need to be applied for the proper length of time and then removed. You should also rinse the brick or concrete after using a degreaser with clean water.
Tar can be removed with a commercial emulsifier, which can be used similarly to a degreaser. If the emulsifier is not removing all of the tar stain, you can use kerosene to remove any of the remaining residue.
Paint
Paint can be very difficult to remove from brick and concrete. Always start with a commercial paint remover that’s made for masonry. Then scrape off as much paint as you can, using a paint scraper and a wire brush. Keep in mind that a rough surface may not allow you to completely remove all of the paint by hand. If that is the case, it’s best to call a professional who can sandblast any remaining paint off.
Rust
Rust can be removed from brick using a solution of oxalic acid and water. To do this, you need to mix a strong solution of 1 pound of oxalic acid to one gallon of water. Use a brush to apply the solution, then hose it off after you have finished applying.
On concrete, a different treatment for rust stains is required. Try a solution of six parts warm water and glycerine and one part sodium citrate to remove the rust stains from concrete masonry or walls. Like removing brick rust stains, you should use a brush to apply it to the concrete and be sure to rinse off the treatment after the rust stain is gone.
