What does the term “efflorescence” refer to in concrete finishes?

The term "efflorescence" specifically refers to the phenomenon where a white powdery residue forms on the surface of concrete due to the migration of soluble salts. These salts are typically present in the concrete mixture or may come from the surrounding materials or environment. When water evaporates from the surface, it leaves behind these salts, which crystallize as white deposits. This occurrence is often seen in new concrete or masonry and can impact the aesthetics of the surface, although it does not usually indicate structural issues.

Other choices do not accurately describe efflorescence. For instance, the formation of cracks due to excess water relates more to issues like shrinkage or settling rather than the crystallization of salts. Changes in color after curing might pertain to chemical reactions or environmental conditions but do not involve the deposition of salts. The presence of air bubbles in the surface area refers to air entrainment issues or inadequate mixing practices, which are unrelated to efflorescence. Understanding these aspects helps clarify why the first option is the correct interpretation of the term.