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Wet CMU foundation


Bob White
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I usually see poured foundations. Today, though, I looked at this house (basement, masonry (CMU) foundation).

All four sides of the foundation were wet. the moisture showed through along the mortar joints.

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Inside the basement, the previous owner (the house has been unoccupied since OCT 05) had "painted" three different areas of the basement with a product (DAMTITE?) to prevent leaks.

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Checks with a moisture meter (designed for wood) showed the dark areas (mortar) at 15% - 18% outside the structure.

Areas with the "paint" inside the basement read less than 6% (I didn't break through the sealant with the moisture probes.

Readings at the base of the basement walls (inside) were off the scale, greater than 23%.

Grading at the house was typical, meaning I saw nothing directing water toward the structure.

This place is in the Northwest Georgia Highlands area. Relative humidity outside and inside the basement was read 38% on my tem/humidity meter.

The house is twelve years old. I saw no evidence of heaving, settling or other anomalies that I could reasonably attribute to these abnormally wet foundation walls. I told my client that I would try to find out more about this phenomenon before making a recommendation.

Could I be looking at underground springs here?

After twelve years with no "damage", can I tell my client to expect no damage in the future?

Is that water deteriorating the foundation?

Those wet walls bother me, but I don't know what to recommend.

Hoping for expert advice from the foundation brain trust,

Bob White

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Bob,

It is pretty common to see the masonry joints telegraphing through parged blockwork. Usually when we applied two coat parging to the exterior of basements before backfill the joints would show through like this the next day. Concrete block, especially older ones, are very porous and water easily passes through them. I believe that the joints give up their moisture slower because the material is more dense (simply sand and cement) and struck (tooled to a smooth slick cementicious finish)which is done to create a good weather resistant surface to the mortar joint.

As far as the high readings at the bottom, the cores probably have water in them which is wicking up the block (if the cores aren't grouted).

Water won't damage the blockwork. Concrete products reach the majority of the curing process in the first 28 days and under ideal conditions that last percentage of cure should take decades. (In an ideal world the half life of concrete is about 100 years) Actually, in the old days, concrete footings were earth or water cured. That is, buried or submerged to insure that the curing process would be purely a chemical process and not rushed by evaporation. So, as funny as this sounds, that wall (structurally) is bound to be as strong as could be hoped for providing static pressure doesn't actually heave it.

Here's an article on the importance and methods of curing concrete products, which includes earth and water curing:

http://www.nrmca.org/aboutconcrete/cips/11p.pdf

I suspect that the exterior waterproofing was poorly done and/or no (or a poor) perimeter drain.

When our masons would put a good cove along the cleaned off footing and two good thick coats of parging properly cured, a thick coat of tar and a perimeter drain our basements were always dry as a bone! But, our two coat parging ended up being pretty thick! (1.5" +/-) Parging is something that masons are notorious for skimping on not realizing just how critical a good thick coat is.

I would not expect things to get any better or worse. What you see is what you get.

That's just my guess.

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Thanks for the quick reply and education.

I too think the builder skimped on the tar (very thin where visible) and probably never installed the foundation drain.

I've found since last night's post that there are many, many springs in the area, lots of water just popping up from the ground.

I guess, then, that as long as the treated sill stays dry, the homewoner can just live with the wet walls and mainain the sealer on the inside walls of the foundation.

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