[log in to unmask] wrote:
> ...they don't efforesce?      Christopher

Chrif,
The brick doesn't effloresce, the mortar does. And any mortar that has 
water behind it, such as from leaks at parapet walls, lintels, etc, will 
effloresce, in my understanding, as the water moves down and from high 
pressure to out and low pressure (open air) through the mortar.

I also saw concrete work in the Harbor in Baltimore (overhead walkway, 
staircase, etc) which was efflorescing from cracks, and the concrete 
wasn't more than 5 or 6 years old. Water wasn't draining properly and 
was soaking into the concrete, or was draining through the cracks, and 
producing white flowery crystal formations on the undersides of the 
concrete structures.

You can also get efflorescence from rising damp as the water is sucked 
up into the masonry and then makes its way out to the lower pressure of 
open air, usually in a basement interior.

Some cave formations are a type of efflorescence - water falling from 
the sky picks up a little CO2 and become weak carbonic acid, which soaks 
into the ground, picks up minerals, and then dumps them on the interior 
surface of the cave as the water evaporates/loses ability to carry them 
in solution.

The water always wants to move to a lower pressure space and dissolves 
and carries the cement from the mortar or concrete, eventually, leaving 
just the sand or aggregate behind. At least that's my understanding - I 
bet someone on here can give us the exact vocabulary, hydro equations, 
and chemical interactions, if we are interested. More than likely, Steve 
S and Mike E.

Judith can probably tell us about inferior mortars to avoid?
~deb

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