THE CORNER COLUMN keeps getting soaked from the inside, upon rainfall, as does the portico slab beneath it. Somehow. And even after we have eliminated several suspected pathways for water intrusion.
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| Rainwater is causing discoloration, bubbling, and cracking of the paint— only on this column, and only on one side. Where is it coming from? |
Last week, the general contractor Yosi Arbib speculated about a possibility that I had not previously considered: whenever rain soaks the planter that is next to the base of the column, moisture is being drawn, via wicking, both up into the column, and down below the column.
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| Yosi’s hypothesis |
It seemed to me that Yosi’s hypothesis would be fairly easy to test. Basically the test would consist of pouring water into the planter, and then seeing whether the column gets damp.
Below the jump, this post documents the experiment that I carried out.…
Summary
Evidence of water intrusion via this channel was not apparent.
Preparing the test
The testing site
The planter was built atop the same slanted slab upon which the stairs were laid. On the 1948 dedication day for the sanctuary building, the planter was still under construction. As this photo shows, the planter is thus rather shallow. We do not think that it is lined with any waterproofing, although it does have drain pipes at the bottom front.
This is the view from the other direction—underneath the corner column and the planter, looking south from under the portico. (The wall shown is at the southern edge of our property. The front steps are to the right.)
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| Looking upward at the SW corner of the portico. (Corroded rebar is a sign of longstanding water intrusion.) |
Test set-up and control measurements
The most recent precipitation was on May 3, a mere 0.03". Previous to that, April 26, about 0.3". Ruben had not watered the planter in recent months. So our column and the concrete was under dry conditions.
Moisture-meter testing on Friday, May 23, registered in the green (=dry) range, roughly 15%. (Because the concrete surface is very rough, the readings are imprecise, maybe ±5%.) The meter passed the calibration test as recommended by the manufacturer. It reads at 5% even when the probes are in the open air.
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| Under the planter |
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| Under the column |
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| CONTROL SPOT: Under the front steps, several feet from the corner |
As a parallel method of checking for moisture, I adapted the methodology spelled out in ASTM D4263, which is a standard and straightforward way to test for moisture in a concrete slab, before proceeding to apply a surface coating.
- Use duct tape to apply an 18” square of plastic sheeting (non-breathable membrane) over the concrete surface.
- Come back in 16+ hrs and look for condensation on the sheeting—which would indicate the presence of capillary moisture in the concrete.
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| Friday, May 23 |
The test
First I secured Ruben’s agreement to keep other water away from the testing site. Then poured about 2 gallons of water into the planter next to the column, within the space of about a minute. It got a dousing.
I watched in surprise as water emerged immediately from the side of the planter. It was quite porous.
Most of the water went immediately onto the steps, heading downhill.
Still, some water did head toward the column (perhaps internally, as well).
Would that be enough to soak the column and the concrete slab underneath it?
No water came out the front drains during the next few minutes. (Not shown.)
Results
I came back 24 hours later. It appeared that some of the water had made its way out the front drains, from which it meandered along the flagstone. That would explain the presence of the small puddles.
Underneath, there was no sign of condensation on the plastic sheeting.
Similarly, after I peeled up the plastic sheeting, the moisture-meter readings did not show an appreciable difference from the pre-test measurements.
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| CONTROL SPOT: Under the front steps, several feet from the corner |
Discussion
I did not find clear evidence that water from the planter migrated into the adjacent concrete underneath the corner column.
An apparent slight elevation in measured moisture at the underside of the slab was not significant; it was within the margin of error of the measuring device.
One variable that may have affected the outcome was the length of time between the introduction of water (in the planter) and the measurement of moisture (in the adjacent concrete). ASTM said to allow 16 hours for condensation to form above a moist concrete slab. In our case, damage in the column was usually evident several days after a rainfall. So I do not have reason to think that 24 hours would yield a misleading result.
Perhaps I should conduct the test again—this time introducing the water slowly, more like rainfall, so that it has a better opportunity to sink into the soil.
Yet the fact that some water did emerge later from the bottom drain suggests that the soil in the planter did get wet to excess.
A future test could also apply the moisture meter to the column itself, at the cracks in the painted surface.
Conclusion
I do not believe that we have found the culprit.
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