- Q.Some of the brickwork on a
house I built has developed a white stain that
resembles efflorescence but is limited to only two
areas: a mailbox and a window. The gutter above the
window overflows occasionally, but the water doesn't
appear to actually fall against the brick. What's
causing the stain, and how do I get rid of
it?
A.Mike DeBlasio, a masonry
contractor in Littleton, Mass., responds:
Efflorescence occurs when soluble salts in the
masonry are dissolved by moisture being driven
through the material via vapor transmission or
hydrostatic pressure. When the solution reaches the
surface and evaporates, a salt deposit —
efflorescence — is left behind.
However, with efflorescence you'd see more
widespread staining at grade and above. The problem
you describe is more likely caused by contact
between aluminum and the brick and mortar. Mortar
is highly alkaline; it will react with an aluminum
mailbox or window frame, breaking down the metal
and causing staining.
To prevent direct contact and reduce the
staining, you should cut the aluminum back, away
from the masonry, and install a proper sealant
joint. Unfortunately, I don't know of any stain
remover that will fix this problem. (Don't use
muriatic acid; it will attack and damage the
mortar.)