What are the White Deposits on Cement After It Rains?

Description

• The white deposits that appear on cement after rain are salt deposits or efflorescence. These salt deposits in the cement mixture form near the surface and are most often visible during temperature changes or after rainfall. The white spots are generally more visible in dark-colored concrete.

Formation

• A number of factors determine whether efflorescence forms in cement. Salt deposits can form from the interaction between carbon dioxide and alkalies or soluble salts. The result is the formation of these salts: sodium and potassium carbonate and calcium carbonate. The rate at which water moves in and out of cement also can create the white salt deposits by increasing the permeability of the material. Increased permeability affects the amount of water that enters the cement; the water then rises to the surface during periods of high humidity. Additionally, the amount of salt inundated with water in the cement affects the formation of the white deposits on cement. Temperature is another factor: It determines how fast water evaporates from the cement.

Prevention

• You need to cure or hydrate newly poured concrete to make sure it solidifies properly. Treating the cement with a dual curing and sealing product helps prevent efflorescence. This product protects the cement by forming a waterproof film over the cement while sealing enough water in to aid in the hydration or curing of the material. Because cement needs water to harden properly, the trick is in controlling the amount of moisture you expose the cement to during this process. Shield the cement with sheets of plastic after you apply the waterproof solution for additional moisture protection.

Removal

• The white salt deposits are generally simple to remove, provided there is not an abnormality in the cement. One way to remove the deposits is to brush away the deposits and use a dry vacuum on the cement. Spray the cement with water in addition to the brushing process for complete removal. Particularly difficult or hard salt deposits might need a stronger removal method such as light sand blasting by mixing fine grit sand with water in a power-washing unit. Use caution with sand blasting; it can alter the texture and damage the surface of the cement with the application. Finally, diluted acid will remove stubborn salt deposits; however, this kind of caustic application typically changes the color of the cement.