Efflorescence is a visible sign that indicates moisture penetration through a masonry foundation wall. This phenomenon occurs when water seeps through the masonry and dissolves soluble salts present in the materials. As the water evaporates from the surface, it leaves behind a white, powdery residue, which is these crystallized salts. This formation is not only a sign of moisture intrusion but can also indicate ongoing or chronic moisture issues, suggesting that the wall is not effectively managing water intrusion.
While mildew, spalling, and cracking can also be associated with moisture issues, they do not specifically highlight the salt deposits that define efflorescence. Mildew is more related to organic growth due to prolonged dampness but does not indicate the moisture's origin within the masonry. Spalling typically reflects the physical breakdown of the masonry from freeze-thaw cycles or corrosion, while cracking focuses on structural integrity rather than the chemical implications of moisture presence. Therefore, efflorescence stands out as a direct and unmistakable sign of moisture penetration in a masonry foundation wall.