What is the primary cause of efflorescence in building materials?

Efflorescence is primarily caused by moisture migration within building materials. When water enters porous materials such as brick, concrete, or masonry, it can dissolve salts present in those materials. As the moisture migrates to the surface, typically through evaporation, it leaves these dissolved salts behind, resulting in a white, chalky residue known as efflorescence. This process is often exacerbated by water movement due to capillary action, leading to visible deposits on the surface.

The presence of moisture is crucial in this phenomenon, as without it, the dissolution of salts and subsequent deposition would not occur. While freezing temperatures, excessive heat, and air contamination may impact building materials or their integrity in various ways, they do not directly lead to the formation of efflorescence. Thus, understanding moisture dynamics is key to both the occurrence of efflorescence and the overall health of building structures.