What does efflorescence appear as on masonry walls?

Efflorescence appears on masonry walls as a white powder or salt-like deposit. This phenomenon occurs when water from the masonry moves to the surface and evaporates, leaving behind soluble salts. As this moisture migrates through the wall, it carries these salts to the surface; when the water evaporates, the salts crystallize, giving the wall a distinctive white appearance. The presence of efflorescence is often an indication of moisture issues within the masonry, which can lead to further deterioration if not addressed.

The other choices do not accurately describe efflorescence. A blue tint would not be associated with this condition; instead, it might suggest other issues such as certain types of moisture ingress or specific chemical reactions. Reddish discoloration is typically indicative of rust or iron oxide coming from embedded metal components, while an oily stain could suggest the presence of oil or grease, which is unrelated to the process of efflorescence. Understanding the characteristics of efflorescence helps in diagnosing the moisture issues affecting masonry structures effectively.