Efflorescence
White crystalline deposits that appear on masonry as moisture brings salts to the surface and they crystallise there.
Efflorescence is a symptom, not a cause. It tells you moisture is moving through the masonry and bringing salts with it. The salts crystallise as the water evaporates at the surface.
Common locations: lower brick courses, around windows, on internal walls where DPC has failed, on chimneys.
Brushing efflorescence off doesn't solve the underlying moisture problem. The salts will keep returning until the moisture source is addressed.
Salt damp
Salt-laden moisture wicking up from the ground into masonry walls. Visible as white crystalline efflorescence on lower courses, blown render, or paint flaking on internal walls.
Rising damp
Moisture rising vertically through masonry walls from the ground, in the absence of a working damp-proof course.