THIS TALE BEGINS in April, when I noticed blistering and peeling paint on the corner column in front of the sanctuary. Along with the other columns, it had been painted less than a year earlier! Meanwhile, the other columns looked fine.
The painter and I guessed that water was somehow getting through the roof and running down the inside of this column. Then the primer was unable to adhere to the moist plaster.
So I tried to get to the bottom of the situation — literally.…
In an effort to confirm that moisture was involved, I went underneath the portico, to find that moisture is indeed showing up there, below the column. Apparently this process has been going on for a while, given that the rebar is rusty and showing through, and all the efflorescence (white mineral deposits). According to my rough measurements, the visible crossed rebar is right under the center of the column.
Water is dripping from there onto the ceiling below — not enough to penetrate, but enough to feed some black mildew or mold on the surface of the plaster board.
In early May, I consulted the roofing contractor with whom we have a service contract. He was unable to find any plausible leak source on the roof. He opined instead that maybe water was wicking up from below, pointing to a gaping hole in the bottom of the column, where the plasterers who formed it (apparently in place) were blocked by the parapet wall from being able to reach in and seal off the column.
Maybe water was getting in there — said the roofer — and wetting the lath’s paper backing and spreading to the whole column. However, I can see bubbling paint way up high, near the very top of the column. It seems unlikely to me that moisture would wick from the bottom all the way up, enough to unseat primer.
Meanwhile, though, it does seem plausible that the moisture underneath the portico could be from rainwater that collects at the base of the column on the outside, before soaking through the pavement surface. It seems to me that such water has nowhere else to go!
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| Detritus in the neglected gap between the column and the parapet wall’s corner |
In late May, I consulted a general contractor who has experience in dealing with water intrusion. He noticed a correlation between where the primer failed to adhere and places where the painter had used a patching compound to smooth out the plaster before painting over it. Apparently that compound was absorbing moisture more readily than the plaster itself.
The painter then told me that he had used DAP Presto Patch, so I chatted online with a product specialist at DAP. I was told that dampness from behind would predictably lead to an adhesion problem. At least that now explained the unevenness of the primer’s adhesion.
So I wondered whether we could find a patching compound whose ability to hold primer wouldn’t be affected by dampness. However, I did not proceed, because I still didn’t know where the water itself was coming from.
Happily, today another water intrusion expert (Bryant Figgins of Absolute Maintenance & Consulting) may well have solved the mystery, just by looking at our façade photo on Google Maps! The problem, he insisted, involves the stucco that covers the front of the overhang above the column.
That makes sense to me. Here’s the scenario: The 14-year-old paint on the surface probably doesn’t provide much outer protection anymore against water. Stucco readily admits moisture. Assuming that the interior moisture barrier (designed to last for 50 years or so) has deteriorated, rainwater that strikes the overhang’s surface may well be finding its way into the plaster of the column below.
Hmm. But why does only that one column seem to be affected? Is it perhaps because its cap is exposed on two sides? Or am I just not looking closely enough at the other columns!?
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