Mold on Concrete Block Walls: Determining source of fuzzy white growth on basement walls

Our Answer

It may be mold but is more likely efflorescence, crystals of mineral deposits left behind when moisture migrates through a foundation wall, and then evaporates.
Efflorescence flakes will dissolve in vinegar or dry up into powder, which mold will not.
To reduce moisture on basement walls, improve your roof and surface drainage conditions outside the foundation wall area.