What does white powder on my brick mean?

The salts that form efflorescence usually come from within the mortar or brick itself, sometimes from the soil or concrete nearby. Water dissolves them, wicks them to the surface through capillary action, and as the water evaporates, the salts crystallize and stay behind as that white, powdery film. It's a common, mostly harmless part of new mortar curing, and a lot of fresh masonry shows some efflorescence in its first year before it settles down as the mortar fully cures and stops giving up as much moisture.

The concern is when it doesn't settle down, or when it shows up heavily on older masonry that's been standing for years. That usually means there's a steady moisture source feeding it, and in the Blue Ridge foothills, repeated freeze-thaw cycles keep pushing water through masonry over and over, which can turn a cosmetic efflorescence problem into the beginning of spalling if the moisture source isn't found. Heavy efflorescence low on a wall, near grade, often points to a different source than efflorescence higher up near a roofline or chimney, so location matters as much as amount.

We brush or wash off the surface deposit, but the real work is tracing where the water is coming from: grading that slopes toward the wall, clogged or missing weep holes, damaged flashing, or ground moisture wicking up with no vapor barrier. Fixing the source stops the efflorescence from coming back and protects the brick underneath, and it's a lot cheaper to trace and fix that source now than to deal with spalled brick a few winters down the road.

• New mortar curing, which is normal for the first year or so
• Poor drainage or grading pushing water toward the wall
• Missing or clogged weep holes trapping moisture in the wall
• Damaged flashing letting water into the wall cavity
• Rising damp from ground moisture with no vapor barrier