After much scrutiny it has been determined by AEON Preservation Consultants (AEON) and Federal Masonry Restoration (FMR) that the chimneys are essentially sound, and only minor repairs are necessary. Our concerns here were that they had been significantly “rocked” during the earthquake in 2011. Several of us were in the basement when we heard, felt and then saw the shock wave travel through the building on that day in August!
Our chimney story begins with photos from the early 20th c the first showing the building in its earliest photographed configuration. In the 1922 image, note that both chimneys are largely intact with corbelled and vaulted tops and appear to be unpainted. The brick on both chimneys is showing some signs of deterioration, as unevenness in the surface is apparent.
The next image taken in 1933 shows that the East chimney top has been rebuilt, but without the corbel and the vault is as a result a little smaller as well. By measurement the East chimney is shorter by the height of the corbel, and the quality of the vault is inferior to the original.They both remain unpainted and the deterioration does not appear to have gotten much worse.
The 1970’s images of the building show it in perhaps its worst state. Aside from cheap roll roofing and a lot of roofing tar applied to seal the chimney and dormer flashing areas, the chimneys have now both been stuccoed over. This is most evident as the corbel details on the West chimney have been smoothed out by the thick coating.
The “as-built”1980 restoration which we are working from in this project diverged somewhat from that proposed in the architects construction documents. Those drawings show restoration and repair of the existing brick work, but a decision was made to retain and repair the stucco over the brick work. Further, in an unusual detail, the stucco was extended over the chimney flashing as a counter flashing, making it impossible for us to replace the roof without disturbing the stucco at the intersection of the roof and both chimneys. This had already failed as cracks had telegraphed through the stucco at the point where it was no longer attached to the brick and simply floated on top of the flashing attached with a strip of galvanized metal lath.
So FMR’s first task was to remove loose stucco and chase cracks that had telegraphed through the stucco, and remove enough material at the base to free up the flashing, and look for signs of catastrophic structural weakness (system discontinuity from the quake and other lateral force events like hurricanes, micro bursts and Durrechos), and systemic weakness (general brick and mortar condition failure) if any.
Much to our surprise (and relief), we found very little of either! Almost all spot checks revealed that other than the changes described above, the masonry was in good, largely original (to 1742 or certainly that era) condition.
As with any building this old few areas of concern do have our attention though.
The chimney step flashing once revealed was found to be consistently very close to the roof level, less that 3″ in some cases. This was contributing to some mortar deterioration below the flashing and perhaps some of the moisture related blistering of plaster in the 2nd floor chambers as water seeped through the system and found it way out.
- The roof along the front and back of the West chimney was flashed to a dramatically sloping roof condition which appears to have been sagging since early in its life. Further investigation of the structural reasons will be included in another post.
- The middle of the brick vault atop the West chimney was sagging significantly and loose brick work was evident, though a very heavy portland cement parge coat remained intact above the brick. From initial visual inspect there was concern it was a sign that the entire vault was in a near state of collapse.
But looking at the 1980 restoration drawing and chimney brickwork below the roof line in the attic AEON and FMR determined that there was a clay flue liner repair apparently conducted at that time and the area of weakness was relegated to that repair only as they had to remove a portion of the vault to prepare chimney and slip the replacement clay liner into the the chimney mass.
So the good news is that the repairs will require less intensive measures that originally though might be required. FMR will finish chasing the cracks resetting the few bricks in the chimneys where loose, and pointing parging with with a natural hydralic lime in several lifts to ensure the integrity of the repairs and seal the surfaces. The surfaces will then be coated with a breathable masonry coating which will be determined once all repairs are complete.