St. Mary's Hall - Boston College
St. Mary’s Hall, opened in 1917 and is the second-oldest building on the Boston College campus, had a distinguished pedigree but was showing its age. The very ornate, Collegiate Gothic four-story building was constructed of Roxbury Pudding Stone with precast or cast-stone decorative elements throughout. But after nearly 100 years, these pieces—which were not well understood or engineered at the time—had begun to fail. To rejuvenate the hall, designers used precast concrete components to recreate the ornamental pieces.
“A key design challenge was faithfully replicating the appearance of the original cast-stone details while at the same time improving the long-term durability of the masonry construction,” explains Wendall C. Kalsow, principal and preservation architect on the project. But the project’s scope was daunting: There were more than 50 pieces of significant “museum quality” sculpture and more than 16,000 total precast units.
Each piece was surveyed, evaluated and given a unique number with specific dimensions before shipping it to the precaster. Damaged pieces were rebuilt by the precaster’s mold team, and new molds were constructed to fabricate new pieces. A high-density liquid resin was used to ensure precision and the proper textural finish. Each piece was molded, cured, unmolded, and treated with a light acid-etch to achieve its final appearance.
Two precast concrete mixes were used, one to produce a granite-like granolithic finish for the base of the building, with a second mix used to replicate limestone. Stainless-steel reinforcements and plastic manipulation anchors were used to add durability and long-term quality. The building was laser-scanned to digitally record benchmarks and provide backup information needed during the reconstruction.
“Very rarely is this quantity of artwork integrated into the architecture of a building,” says Kalsow. “To successfully replicate these elements in precast concrete not only shows the versatility of precast but also demonstrated the high level of skill of the artists, precaster, mason, and general contractor involved in the project.”
To save time and complexity, some of the smaller pieces were combined to create larger units with false joints. Most pieces featured a six cut-line finish executed in wet-cast, which produced a challenge at window traceries that required extreme precision and delicacy in the execution, he says. Each of the 28 tracery windows had 17 pieces of cast stone, which led to the tracery sections to be cast as one unit. It was constructed by assembling two precast sections in the fabricator’s shop, which allowed the inner and outer halves to be cast with the visible face down for the highest quality control. This approach reduced the number of tracery stones needed from 478 to 28.
The work represents the largest cast-stone restoration project undertaken for a historic building in North America. The cast-stone required a special concrete mixture to fit the owner’s expectations and their historic-preservation specialists while offering a guarantee for durability and quality.
“While precast concrete is often thought of as only a modern architectural material, it can also perform extremely well in significant historic-restoration projects replicating either cast or natural stone,” says Kalsow.
Precast Concrete Consultant:
Engineer of Record:
Architectural Precast Elements:
• Units weighed from 5 pounds to 4,150 pounds.