What is not considered a cause of efflorescence?

Efflorescence is a common phenomenon in masonry where soluble salts within the material migrate to the surface and crystallize, typically due to moisture. High humidity and excess water during curing can indeed contribute to the movement of these salts, as they provide the moisture necessary for the salts to dissolve and rise to the surface. Poor drainage also plays a significant role, as improper drainage can lead to increased moisture retention in masonry materials, promoting efflorescence.

On the other hand, extreme temperature shifts do not directly cause efflorescence. While temperature can affect the rate of evaporation and potentially influence moisture levels, it does not facilitate the process that brings salts to the surface in the same way that the other conditions do. Therefore, extreme temperature shifts are not considered a primary cause of efflorescence compared to the other options listed. This distinction helps clarify why this choice is considered the correct answer.