What causes efflorescence on concrete surfaces?

Efflorescence on concrete surfaces is primarily caused by moisture carrying soluble salts to the surface. This process occurs when water infiltrates the concrete and dissolves naturally occurring salts found within the material or in the soil beneath it. When the water evaporates from the surface, it leaves behind these salts, which appear as white, powdery deposits.

The formation of efflorescence is a common issue in concrete and masonry, especially in environments where there is a high level of moisture or where concrete may be in contact with water, such as in basements or exterior walls. Understanding this mechanism is crucial for coatings inspectors, as efflorescence can affect the adhesion of coatings applied to concrete surfaces and may indicate underlying moisture problems that need to be addressed prior to any painting or sealing work.

As for the other options, they do not directly cause efflorescence or address the chemical processes involved in it.