A number of years ago, I grouted a similar late 19th century cavity wall for a project in Boston's North End. This was a late 19th century multistory commercial building originally built as a candy factory, and repurposed over time. In the mid to late 19th century, this kind of wall assembly was common in New England, especially in multistory buildings, as a method to save weight and material.
In my project, the walls exhibited cracks and were not watertight. Because there were no weep holes, and no practical means of draining the cavities with new weep holes, I opted for grouting with a fine grout mixture inserted through multiple ports in minimal lifts. At this building, the wall did not have continuous cavities - like many examples of its era, the walls had multiple cavities that were discontinous. The grouting had to be monitored carefully to prevent seepage, and the quantity limited to prevent blow out. The project worked well. The grout mixture must be fine, with curing and viscosity carefully selected. This grout mixture was very different than the types used for grouting CMU. I used a mixture with polymers.
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Marsha Levy AIA
Boca Raton FL
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Original Message:
Sent: 02-21-2020 11:49
From: Jeffrey Heyne
Subject: 1876 brick cavity wall, Back Bay, Boston
Hi Historic Resources Committee,
We are renovating a 145 year old 5 story brick townhouse on Comm Ave in Boston's Back Bay. The shared party walls are solid 12" thick 3-wythe brick bearing walls. The rear facade facing the alley has a shallow brick curving bay from grade to the 4th story.
As an elective partial seismic upgrade, our structural engineer has designed 4' long steel angles bolted horizontally to the interior face of the brick bay just below the floor joists, with steel strap tie-backs bolted to a few of the floor joists--essentially tying the floor diaphragm system to the brick wall. The floor joists span party wall to party wall, so they run parallel to the rear curving bay wall.
Upon drilling and bolting the steel angles, we discovered the curving brick wall is a cavity wall--12" thick but the center wythe is missing. There are brick header ties bridging the inner and outer wythes at around 32" o.c. Our structural engineer assumed the wall was solid and drilling and bolting would find ample solid masonry to anchor into.
We are now considering injecting grout into the cavity in working from bottom up in shallow layers in order to mitigate blow-out the brick wythes from too much grout. Sounds good but we are worried about this.
We all assumed the curving brick bay wall was solid and functioned like any normal traditional masonry moisture reservoir wall system. But this cavity wall has us puzzled. It seems like it could function to retard liquid water drive through the outer wythe, but we see no evidence of weeps at the bottom. If we make the wall solid by injecting grout we may affect the way the wall handles water and could be deleterious. From our inspections it appears this wall seems to be handling rain/snow/ice/moisture in a satisfactory way. We see no mold in the cavity, but we are planning to repoint and rectify the flashing issues.
We endorse the partial seismic upgrade as a benefit, but are worried the grout injection could potentially create an unknown water intrusion problem. Has the Committee come across any similar cavity wall situations, and how were they dealt with? Any thoughts would be helpful.
Thanks,
Jeffrey Heyne AIA
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Jeffrey Heyne AIA
Boston MA
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