Chalky White Substance
Concrete is made up of limestone, clay and mortar, and aggregate (stone). That white outline or spot you see is the calcium in the block leaching out. It’s an indication of water, excessive moisture, and is something you should pay attention to. It’s called efflorescence.
 Heavy White Chalking |
 High humidity will cause condesation. This leads to the white, chalking walls you see here |
Efflorescence is a sign that water or moisture was absorbed into the masonry, cement or concrete at one time. The moisture in the masonry walls and floor, has dissolved some of the water-soluble ingredients like lime and calcium. When these minerals dry out, crystals form, leaving the chalky efflorescence.
There can be a number of causes for this type problem
High Humidity – If high humidity is the cause of your problem, the white residue will usually be uniform over a large broad area. Often times, you can see staining up to a certain height on the wall and it occurs at a generally consistent height. Condensation causes beads of moisture to form on the cool surfaces and is absorbed into the porous cement.
Wall Cracks and/or Failed parging – Once you get a crack in your masonry walls, the parging that keeps out water, fails. Because the masonry is porous, it will wick in water or moisture. When the moisture dries out, the minerals and other water soluble ingredients that leached out, begin to crystallize.
