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  • In Detail> Shepard Hall

    Elemental gives George B. Post's Gothic City College landmark a long-in-coming restoration, gargoyles and all
    The Gothic revival Shepard Hall in Hamilton Heights, built in 1907, has new glass fiber-reinforced concrete decorative trim in place of original terra cotta.
    Courtesy Elemental
    Designed by George B. Post and completed in 1907, City College’s Shepard Hall is in all probability the most faithful specimen of English Perpendicular Gothic revival architecture in the United States. The first structure to inhabit the institution’s Hamilton Heights campus, it was modeled on a cathedral plan, its main entrance within a bell tower on St. Nicolas Terrace that connects two flanking academic wings and a central great hall for assemblies. Like many of its Gothic predecessors, unfortunately, the building also featured certain flaws that, over time, led to severe deterioration in the building’s fabric and the threat of catastrophic structural collapse.
    the team replaced some 70.000 pieces of deteriorated terra cotta (left) with the gfrc product (right), which could be used to mass-produce repetitive decorative elements. 
    Post constructed the hall primarily from local schist—stone quarried during the excavation of the site—and terra cotta, which makes up the decorative elements. He used the terra cotta, however, structurally, as if it were just another piece of masonry. While terra cotta is very strong under compression, it has almost no tensile properties. As a result, when water infiltrated the walls and as the building swelled and contracted with the changing seasons (it was built without expansion joints), the terra cotta could not handle the stresses as well as the schist, and so it began to crack, break up, and come loose. By 1986, when architecture firm Elemental (then The Stein Partnership) answered an RFP to restore and reconstruct Shepard Hall’s envelope, pieces of terra cotta the size of grapefruits had been falling off the building with regularity for some ten years. Only one third of the original material remained. The rest had been filled in with bricks and stucco. From the outset, the architects decided that in replacing the terra cotta, they would employ a rain screen system with a light, thin-shell material fulfilling the decorative aspects and a separate material taking on the structural role. The material would also need to be mass-produced in order to meet the reconstruction schedule. Some 70,000 pieces of terra cotta needed replacing, 3,000 of which were completely unique sculptures—allegorical representations of academics, gargoyles and grotesques, and vegetative motifs. The team considered terra cotta, but the material was quickly ruled out since it would have taken decades to produce the needed pieces by the two manufacturers in the country who could do it at all. They settled on reinforced concrete (GFRC), basically a Portland cement with significant chemical variations. It uses only fine-grain aggregate, a small amount of polymer, glass, and carefully controlled sand.
    the thin-shell replicas were bolted back to a new masonry structure, with soft joints between the new masonry and original schist.  
    A sprayed product about 3/4-inch thick, the GFRC offered the possibility of speeding up the fabrication of all of the repetitive pieces and keeping cost down. The sculptural elements took a little more time. Those that remained more or less intact were removed from the building, touched up, and used to form rubber-lined production molds. Those that had vanished were recreated from old photographs or extrapolated from fragments. The GFRC system offered a much higher level of precision than did the original process. To be as faithful as possible to the original, Elemental took care to introduce the imperfections characteristic of terra cotta, including tooling marks, irregularities on flat planes, and slight variations in the “white” color from piece to piece. The team filled in the structural gaps left by the terra cotta with traditional masonry structure, and bolted each thin-film replica back to the new masonry. This allowed the creation of soft joints between each piece and the existing schist. When taken across an entire elevation, these small, soft joints comprise a de facto expansion-joint system capable of accommodating significant building movement. In the course of replacing the terra cotta, the architects uncovered a number of other issues that needed attention. The bell tower was discovered to be in a state of structural failure. Steel supports in the existing masonry had corroded to the point of no longer being there. All that was holding it up was the terra cotta, some rubble stone, and a chicken-wire wrapper placed there to keep the gargoyles from falling onto students below. It was completely rebuilt, the cladding removed, a new precast, post-tensioned concrete structure inserted, and then the new thin-film elements attached. Elemental divided the project into ten contract packages, ordered according to severity of need, and tackled them when the budget became available. The firm is now finishing the ninth package. Although not among the gargoyles, the spirit of George B. Post might well sit smiling, twirling his Edwardian whiskers in hearty approval.
    Aaron Seward

  • The Cathedral Stone Newsletter

    Historic Brick Wall Scheduled for Demolition Saved by Jahn M30 The Cathedral Stone Newsletter, July 2006

    The condominium complex at 241 Eldridge Street was constructed in 1904 in the Lower East Side of Manhattan. Architect Scott Henson was hired by the condominium board to perform a full exterior analysis of the building. The analysis revealed a number of necessary repairs, including brick, window, and terra cotta replacement and repairs, mortar joint cutting and re pointing, as well as the replacement of the roof membrane and cornice. During removal of the parapet walls, the internal conditions of the brickwork and mortar were found to be severely deficient. The back-up masonry was loose laid in many areas with no mortar.

    The failures of this building were directly attributed to the mortar. The mortar used in the original construction of this building consisted of a high-lime content resulting in little or no binding between the mortar and the bricks. The mortar within the walls was loose and powdery. Adverse weather conditions and poor maintenance over the life of the building accelerated the deterioration of the mortar. Several structural engineers were invited to the building to inspect conditions and provide recommendations. The consensus was that the walls required complete reconstruction from the ground up. This solution was prohibitively expensive for the building owners; therefore and extensive search was undertaken for an alternative solution to repair the internal condition of the walls. After the research and testing of many masonry techniques and products, including mechanical pinning, brick repair products and soil consolidation products, Cathedral Stone Products' Jahn M30 Micro Injection Grout was found. When injected, Jahn M30 will travel into the substrate and continue until it flows freely from this port and other ports at the same level. The ports are then sealed using non-staining clay, sealant, or caulk. A series of injection ports must be drilled on the face of the substrate to create a "drill frame." Ports should be drilled in a downward direction. Cathedral Stone Products, Inc. supplied Jahn M30 Injection Grout for a test area. Cathedral Stone Products representatives, including Dan Perakes, conducted the initial testing on the building. A second and larger test was performed to confirm initial results. This test involved injecting the Jahn M30 into specific areas in the walls to determine whether or not the repair process was going to work. Jahn M30 again proved successful. Extensive testing was performed until the correct installation procedures and amounts of grout required were determined to consolidate the existing lose, powdery mortar, to fill the voids between the internal brickwork, and ultimately to provide a structurally stable building. It was originally thought that the cost to replace the exterior walls would be an estimated $1.8 million. The repairs would have to be completed section by section. Because of the success of Jahn M30 the entire project cost was $106,000 saving the owners over $1.6 million. Scott Henson Architects hired Viles Contracting Corporation to complete the repairs. From February 9th to April 22nd, 2005, they drilled 1,435 holes into the building and pumped in 1,280 gallons of the M30 Injection Grout. After 241 Eldridge Street was completed, the project was featured in the NY Times and drew interest from the engineers with the New York City Housing Authority (NYCHA). They wanted to look at the project to see if the repair method was a viable alternative for maintaining their buildings. They met with both Cathedral Stone Representatives as well as Scott Henson. In the summer of 2005, CSP successfully completed Jahn M30 Injection test of the New York City Housing Authority. They are currently monitoring the tests and are considering using the method of restoration for future projects.         Go to Cathedral Stone Newsletter