Diagnose efflorescence versus subflorescence on a masonry wall and remediate by addressing the underlying moisture source

Steps

1. Visually distinguish the condition: efflorescence is a white, powdery salt deposit sitting on the masonry surface, while subflorescence is salt crystallization occurring within the pores below the surface, often signaled by spalling, powdering, or crumbling of the masonry face rather than a visible surface deposit alone
2. Identify the moisture pathway feeding the salts: rising damp from grade, roof or flashing leaks, condensation, or moisture trapped by a prior hard/impermeable mortar or coating
3. Do not simply brush or pressure-wash away surface efflorescence as a complete fix — treat it as a visible symptom prompting investigation of the moisture source
4. For active subflorescence causing spalling, assess the extent of unit damage and evaluate whether affected brick/stone units need dutchman replacement in addition to addressing the moisture source
5. Correct the moisture source (grading, flashing repair, downspout discharge, interior condensation control, or removal of an impermeable prior coating/hard mortar) before any cosmetic cleaning or repair, since salts will keep re-forming otherwise
6. Once the source is controlled, remove residual surface efflorescence using the gentlest effective method (dry brushing or light water washing) and allow the wall to dry out over a full season before finishing repairs