WE NOW HAVE a plan for how to repair the three deteriorated pilaster bases on the exterior of our historic sanctuary’s south wall. (These bases’ condition is described and shown HERE and HERE.)
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| Detail from structural engineer’s drawing: view from above. E = existing element. (As usual, click/tap on an image to enlarge it.) |
In January, the board approved a budget for this repair. Last week, our structural engineering consultant provided a plan, in the form of a drawing. I’m now asking vendors to bid on doing it according to that plan.
This post briefly describes our plan — as well as what went wrong that led to the need for this repair.
Why is this repair needed?
When these protruding bases were constructed 75 years ago, their internal rebar was located too close to the surface, and also the surface was not waterproofed. Over time and much rainfall, the rebar inside got too moist and rusted. Rusting iron expands, causing the surrounding concrete to crack and spall. Cracked concrete is neither strong enough to help the foundation wall, nor stable enough to hold stucco (and a planned new waterproof coating) on its surface.
What is the plan for repair?
The engineer’s guidance applies only to the two deteriorated bases that have wooden posts inside the pilaster (#1 and #2). Those posts play a major role in the building’s stability, so the engineer advises caution. Indeed, because the wooden post extends a bit outward beyond the concrete stem wall, it’s not 100% supported by that foundation. So the engineer cautions the repair crew: Avoid cutting into the wall more than 5/8”, so as not to undercut the post too much.
Furthermore, he adds that lateral shoring of the post ought to be set up in advance, as a precaution, in case a deeper cut might inadvertently be made during the process of repair. Fortunately for us (in terms of cost), vertical shoring is not deemed to be warranted.
After the damaged concrete and rebar are removed, new rebar is to be positioned, starting from 12" below grade. The rebar is then hooked into the stem wall via U-shaped metal ties that are placed into drilled holes and attached with epoxy cement. Then concrete is poured into a temporary frame around that metal armature.
As for the base to pilaster #3, it is merely cosmetic, because there’s no post inside that pilaster. (It marks the boundary inside between the foyer and the main hall. At that point, a transverse interior wall holds the wall in place, rather than the 5 post-and-tie-rod sets that support the roof in the main hall.) Therefore this base can be rebuilt without a particular structural concern and fancy ties.
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