Identifying the Source of Stairwell Efflorescence

PUTTING OUR HEADS TOGETHER, the asbestos inspector and I came up with a new hypothesis for why efflorescence has for years been showing up on the walls of the stairwell that goes down to the Social Hall.

Years ago, someone (Sonia Cummings?) covered these walls’ lesions with butcher paper.
(As usual, click/tap on a photo to enlarge it.)

My new understanding fits the data pretty well. Below the jump, I will explain — and offer a prognosis.…

Executive Summary

This efflorescence is probably caused by the same defect in the original construction that has long plagued the sanctuary’s south wall in the same manner: a lack of exterior waterproofing of the above-grade portion of the concrete foundation. 

The problem can therefore be expected to persist until the outer wall is waterproofed. However, it could be reduced (but probably not eliminated) by caulking the outer surface’s cracks and repainting the exterior.

Background

On efflorescence, see my discussion of the south sanctuary wall HERE.

If I recall correctly, Brett told me that those stairwell walls were cleaned up and repainted back in 1997 (i.e., 25 years ago). And I seem to recall a more recent effort, as well. In short, the efflorescence keeps coming back nonetheless. 

Until recently, I had assumed that it was caused by water intrusion from the roof. Hence now that the roof is properly maintained, in theory it is safe to repair and repaint the stairwell. But now I have serious doubts.…

Key Facts

Let us note, first of all, how these walls appear to be constructed. They have a thicker portion at the bottom, and a thinner portion above. This suggests that the thicker portion is actually an extension of the concrete foundation, which here at Main Street protrudes several feet above grade because the ground slopes toward the bay between Hampton and Main.

The core of the thicker portion of this wall is probably concrete,
as on the south side.

The south face seems to have some cracks that arguably admit rainwater readily;
the rain that runs down the wall may also soak the lip of the foundation.

Let us also note the particular location of the efflorescence: It is showing up only on the lower part of the wall (which argues against a roof leak). And it is showing up at basically the same height above grade as the foundation wall. (See photo above the jump.)

In other words, the same problem exists here as along the south wall of the sanctuary, as discussed HERE. Namely, the original construction neglected to waterproof the outer surface of the above-grade portion of the foundation wall. Thus, whenever it rains, moisture crosses the stucco and soaks the concrete wall. The moisture evaporates upon reaching the inner wall, leaving salt deposits on that wall surface. 

Implications

Efflorescence will continue whenever the outer wall gets wet, until the outer wall is waterproofed. (Either by removing the stucco layer long enough to waterproof beneath it, or by coating the stucco with a waterproof membrane.)

Lingering Question

What is the role of the awning, and of the exterior half-pillar, in either admitting moisture into the wall or repelling it?