Abbot Restores Historic 8-Story
Back Bay Building
Abbot recently performed a comprehensive restoration project at 12 Commonwealth Avenue in the heart of Boston's Back Bay district. The historic eight-story building consists of 4-1/2 floors of brick situated between pre-cast concrete upper and lower floors.
Recognizing that the building was in need of restoration, the owner hired Commercial Construction Consulting (Boston, MA) to investigate the problems, develop the plans and specifications, and bid out the job to a select group of bidders. Importantly, the specifications had to be reviewed by the Back Bay Architectural Commission to assure that all restoration was consistent with their regulations. Abbot was the low bidder and was selected as the masonry contractor.
The project was performed in two phases -- Phase 1, where the majority of the work took place, consisted of the front of the building, while Phase 2 involved the rear of the building including the courtyards.
Phase 1: July-December 2010
The front of the building consists of fabricated ornamental pre-cast concrete and slate mansards on the upper two floors, brick in the middle floors, and pre-cast concrete on the lower two floors. Significantly, the front entrance is adorned with an elegant canopy supported by two ornamental steel linked chains.
The problems identified in the front of the building included:
- Severe deterioration of the ornamental pre-cast concrete at the top of the building
- Deterioration of the slate in the mansard as well as deterioration of the steel lintels over the windows in the brick section
- Minor deterioration of the pre-cast concrete at the bottom of the building
Replacement of the ornamental pre-cast concrete at top of building required Abbot to fabricate a 6' x 5' decorative pre-cast concrete pattern to replace the original pattern. Significantly, Abbot needed to match the pattern that was still in tact on the opposite side of the building.
Abbot also replaced several pre-cast arched surrounds around the top floor windows, as well as several pre-cast cornice stones in the top floor area.
In the brick section of the building, Abbot replaced the steel lintels, and repointed the entire area using mortar whose color was chosen by the Back Bay Architectural Commission.
At the same time, Abbot also performed roofing repairs, including replacement of the slate on the mansard, and replacing both of the barrel roofs on the seventh floor.
Upon completion of all of the repairs, Abbot sealed all of the pre-cast concrete with a protective elastomeric coating whose color was also chosen by the Back Bay Architectural Commission.
As part of the restoration project, the building owner agreed to restore the ornamental steel canopy, situated over the front stairway, that had deteriorated and become fragile over the life of the building to its original appearance. According to the regulations of the Back Bay Architectural Commission, Abbot carefully removed the canopy, chains, and chandeliers, and stripped all of the paint. Then Abbot structurally reinforced the canopy, restored all of the ornamental rosettes and flowers to their original detail, and repainted, reglazed, and reinstalled the canopy.
Abbot also re-engineered the drainage system including installation of PVC downspouts to prevent future water damage to the canopy.
During the restoration, Abbot removed the steel front doors from the building entrance, and created a temporary passageway for security during construction. Upon completion of the project, Abbot restored and reinstalled the doors and ornamental grills.
Phase 2: April-May 2011
In the rear of the building, Abbot replaced the most severely deteriorated pre-cast concrete headers and sills, and repointed the brick walls that had deteriorated over the years. In the courtyard, Abbot removed and rebuilt portions of the brick walls.
To reduce the potential for mortar bridging, a 2-inch cavity is recommended. However, investigations of masonry structures have shown that unless a deliberate effort is made to eliminate mortar droppings, even a 2-inch cavity can be bridged. The simple solution to this problem is to assure that mortar spread as a bed joint is beveled or sloped away from the cavity (Fig 1). This practice requires little effort and is an effective means of keeping mortar out of 
Just a single mortar dropping covering a weephole can prevent that weephole from working properly. To reduce the odds of that occurring, the designer may specify that a porous drainage material such as pea gravel cover the flashing at the bottom few inches of a cavity (Fig. 2). Alternatively, manufactured drainage fabrics are available for this purpose. However, these measures are not a substitute for a concerted effort to keep the cavity clean.