How does efflorescence occur?
Water is necessary to make the concrete. Rain, moisture from dew or even water from your sprinkler system reacts with the free lime in the cement forming calcium hydroxide. As the concrete product dries out, the water migrates to the surface through the pores in the concrete product carrying with it the calcium hydroxide. When the calcium hydroxide comes in contact with the carbon dioxide in the air, a hard white substance, which sticks to the surface of the concrete after the moisture evaporates forms. This is the frost or efflorescence that you see. It will continue to form so long as the concrete is curing and the calcium hydroxide is free to move to the surface. The efflorescence phenomenon will stop when no more calcium hydroxide forms.
