A lost art
Once the tallest structure in New York City's midtown area, the 1912 Candler Building is 24 stories of highly ornamented windows, balustrades and cornices, adorned with white terra-cotta tiles. The freestanding tower also boasts what, at the time, was a cutting-edge, smoke-free egress design that allowed the tower to forego the traditional, if unsightly, open metal fire escape.
Despite its innovation, rich ornamentation and unique history (see "The Candler Building: A short history," page 46), by the early 1990s the Candler Building stood vacant and deteriorating, literally crumbling piece by piece at the center of a Times Square riddled with filth and despair. Lost in a sea of mammoth billboards, neon pop-art advertisements and a giant smoke-ring-blowing head, the old tower was structurally sound-but in danger of losing its skin.
By 1993, when Massachusetts Mutual Life Insurance Co. took ownership of the building, the Candler was one of the last remaining white terra-cotta skyscrapers left in Manhattan. The insurer resolved to restore the landmark that stood at the epicenter of a timely, state-funded effort to revitalize Times Square. Swanke Hayden Connell Architects (SHC), New York City, with consultant Theodore Prudon-a professor of Historic Preservation at Columbia University who had prior experience with the city's landmark terra-cotta towers-were retained to evaluate the structural condition.
What the team discovered was a building on the verge of literally blowing its skin right off. Green clay roof tiles were falling to the street below, and more than 75 percent of the terra-cotta and granite joint mortar had failed. Water had infiltrated the structure's walls through mortar joint failures and through the leaking high-slope roof.
The first task was to replace the clay tiles with a historically hued, adhered system, with standing-seam metal battens that replicated the green clay ornamentation. Once water could no longer enter the structure from above, attention was turned to the terra-cotta skin.
The structural cladding was then carefully cleaned, which restored the original appearance of the cream-colored glazed terra-cotta exterior. However, it also revealed significant problems in the façade materials, according to Joseph Soehgan, principal of Diamond Waterproofing, Bethpage, N.Y., a subcontractor specializing in the cleaning and resealing of building exteriors.
"We literally went up on the scaffolding and tapped and stress-tested the anchorage of each terra-cotta biscuit," says John Jappen, SHC senior associate and the project's exterior project manager. Failures in most of the terra-cotta mortar joints-and in more than 50 percent of the brick mortar-had significantly damaged the integrity of the building's outer skin. The majority of the terra-cotta panels had some kind of damage, Jappen notes.
"Most high-rise terra-cotta buildings experience an initial expansion problem in the first two or three years after the building is completed," says Prudon. Also, by 1913, terra-cotta was often only glazed on the visible side, and was kiln-fired only once, thereby allowing the clay tablets to "rehydrate" when exposed to moisture (see below). "The pressure on the mortar joints becomes highly stressed," he says, "and some of the biscuits experienced external vertical cracking as a result of 500 to 5,000 psi [pounds per square inch] of internal hydraulic pressures."
To compound matters, 1913 construction methods typically called for black iron for almost all metalwork. While the structural skeleton was painted for fire and deterioration protection, angles and fasteners usually were not. Thus, the same moisture that was rehydrating, expanding and damaging the terra-cotta panels was also rusting and deteriorating the strap anchors that held the terra-cotta in place.
Clearly, restoring the outer skin of the Candler Building was going to be no small task. Further complicating restoration efforts was its location at the heart of bustling Times Square, not to mention the height of the scaffolding required to inspect and repair the terra-cotta elements. "Sometimes the wind would blow while we were up there," Prudon recalls, "and you'd look down and you were out over the street."
400,000-sq.-ft. jigsaw puzzle
Where the metal anchors had failed but the terra-cotta panel was repairable, SHC called for the panels to be pin-drilled and injected with epoxy. "Once the epoxy set," Jappen explains, "the pins were removed and the panels were secure." This method was utilized where the original materials could remain as part of the exterior finish.
More complicated was replacing the exterior cladding where it was beyond repair. "We employed a two-part replacement methodology," notes Prudon. "Irreparable terra-cotta members were replaced with cast-stone panels that were coated to resemble the original materials." Limited manufacturing options-and budget and schedule-helped dictate the use of an alternative material. But so did other factors.
While all terra-cotta finishes reveal a naturally occurring patina by virtue of the artisan's hand, the clay's chemical composition, the varied thickness of glazing materials and a modern, uniform approach to mass reproduction might give the building a blotchy appearance. "Besides," says Soehgan, "matching a 100-year-old fired glaze would be next to impossible." In this case, that was a good thing.
The reason is that the Candler Building is listed on the National Register of Historic Places and, as such, is subject to Section 106 of the Secretary of the Interior's Standards for Rehabilitation. The standards require that when restoring masonry to such a structure, the new material must match the original in appearance, yet must also be visibly different as to be identifiable as not the original material during subsequent renovation efforts. While this "similar but different" mandate often proves a challenge for renovation architects, in this case it was a benefit.
"There are only two full-scale manufacturing operations that produce architectural terra-cotta in the United States," says Prudon, "and the type of detail required for a renovation like this would have been financially and schedule prohibitive. We couldn't wait five or six months."
Instead, the building team came up with a two-part replacement philosophy. Cast-stone panels were created on site under the direction of general contractor Lehrer McGovern Bovis-now Bovis Lend Lease-of New York City, allowing for exacting fits, replicating the handmade appearance of the original. The concrete replacement material was then sprayed with a coating material to match the glazed appearance of the original biscuits. By fastening a concrete skin to the structural skeleton, these elements essentially became part of the structure.
On the other hand, decorative details, window lintels and ornamentation were treated differently. The building was erected before the advent of the shelf angle, so two strap anchors held the elements in place, with backing brick worked to meet the skin material. For that reason, the building team chose to recast elements in glass-fiber-reinforced concrete (GFRC), which gave the needed impact strength at up to 50 percent less weight than the original materials. The decorative elements were also coated to match the remaining original ornamentation.
According to Arman Azak, project manager and engineer with New York City-based structural engineer Severud Associates, the restoration of the building's exterior surface did not add to the load placed on the structural skeleton.
With the tile cladding secure, the building team then replaced the windows that had been added in an earlier renovation with three-part aluminum windows that replicated the original window appearance, and replaced the metal curtain-wall panels in the center bays. The interior was completely stripped to the structural subfloor, and new elevators, fire stairs, restrooms and office space were constructed.
Under advice from SHC, the team chose not to restore the decorative terra-cotta S-curve balustrades and finials that graced the four corner balconies of the original design. "We needed to hold a line on costs," Jappen recalls, and the remaining original details were removed and photographically recorded for future restoration. The balustrades sat upon a solid, 4-ft.-tall parapet, so the railing was not code mandated.
"The tower is open on all four sides," says Jappen, "so the office spaces in this building are afforded terrific natural light for a skyscraper." The Candler Building, restored to its bright terra-cotta brilliance, sits between a Disney company store and the new Madame Tussauds wax museum-in a revived Times Square.