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by Alan Joch

Under the microscope

For high-tech diagnostics on a par with the forensic science seen in television dramas, Wiss, Janney, Elstner Associates (WJE) operates its own materials-testing lab at the company’s headquarters in Northbrook, Illinois. “If we suspect a problem with a particular material, we send it to the lab for analysis,” says Kyle C. Normandin, an architect with WJE’s New York office. “It makes our job that much more thorough.” His firm is using the lab on an ongoing restoration of New York’s Metropolitan Museum of Art’s facade on Fifth Avenue. Samples of its Indiana limestone went to the lab, where analysis revealed that problems around the mortar joints weren’t allowing water to escape off the facade quickly enough. Lab technicians determined that the cement-to-limestone ratio in the mortar contained too much of the former. Architects are now repointing the area with a more effective composition.

The Fifth Avenue facade of the Metropolitan Museum of Art, undergoing restoration by Wiss, Janney, Elstner Associates. Photography: © Leslie Schwartz Photography

Similar detective work is aiding Fallingwater. Pamela Jerome, senior associate for preservation at the architectural and engineering firm Wank Adams Slavin Associates (WASA) in New York, joined the sleuthing when WASA was hired to guide the Fallingwater restoration effort. Part of her work consisted of restoring the interior paint finishes. WASA collected paint samples and sent them for analysis to an outside testing lab, where technicians were able to determine the number of paint layers that had been applied to the interior, the chemistry of the paints, and their exact colors. “The lore of the house was that the exterior and the interior were painted the same color, and that appears to be true,” Jerome explains. But soon after Fallingwater’s completion, someone repainted the interior a much lighter shade. Jerome knows the house was repainted quickly because the analysis showed very little dirt trapped between the first and second paint layers. “We speculated that the family found the interior to be dark and decided to tone it up a few shades,” Jerome says. “Or it could have been Frank Lloyd Wright who made the decision. He fussed with the building long after it was built.”

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Silman Associates used a number of other diagnostic tools to assess Fallingwater’s structural integrity. Engineers relied on a structural analysis program from software maker SAP AG to model the building’s settling pattern. Motion monitors logged data on cracks in the concrete for a year and a half, and the staff then plotted seasonal fluctuations in the sizes of the cracks as well as overall movement trends. To bolster this data, a surveyor pinpointed elevations along the parapets, and these numbers were compared to those on the original drawings. Taken together, the data showed a slow, steady sagging of the terraces from their original positions.

Matteo says that while the data revealed stress points, technology couldn’t answer the question on everyone’s mind: How much longer would it be before Fallingwater’s terraces failed? Stories had surfaced during Fallingwater’s construction that the reinforcement of the concrete terraces specified by Wright was inadequate, and rumor had it that the builder doubled the number of reinforcing rods Wright had called for, but no one could verify this claim.

To answer this question, Silman hired GB Geotechnics (GBG), of Cambridge, England, to inspect the reinforced concrete using impulse radar. GBG used a transducer to send a radar wave into the concrete, which reflected the wave back to the surface when it detected reinforcing steel. The transducer sent readings to a data recorder, which then created a rough image of the underlying structure. Engineers compared these readings to the original drawings. The result: “The builder did double the reinforcing,” Matteo says. “This was important to know so we could define the building’s existing capacity.”

Pragmatic preservation

Graham believes that nondestructive diagnostics will become even more important in the years ahead. They allow preservationists to surgically find and fix hidden problems without causing excessive damage. “Because we’re more educated about how to evaluate existing buildings, it costs the same or less to fix one that’s already standing than to build a new building,” he says.