masonry, stone, brick, chimneys

Best Face Forward

Philadelphia City Hall is one of the finest examples of French Second Empire architecture in the country. Its vast marble and granite facades are adorned with more than 250 monumental marble and bronze sculptures; following a three-phase exterior restoration project by VITETTA in association with Kelly/Maiello, they are brighter than ever.

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By Lynne Lavelle

More than 260 monumental marble and bronze sculptures and motifs by Alexander Milne Calder adorn the façade of Philadelphia City Hall, which recently underwent a three-phase exterior restoration project by VITETTA. “Meditation” – a seated figure located on the upper level of the west center pavilion – was one of many statues directed to face prisoners using the entrance; Calder hoped that these allegories would encourage those headed to the courts to reflect on their lives. All photos: VITETTA

Though it lost the title of "tallest in the world" shortly after its construction, Philadelphia City Hall remains a building of many distinctions. At 548 ft., it is the tallest load-bearing masonry structure in the world, with foundation walls up to 24 ft. thick. Each of its principal seven floors contains nearly four acres of space, making it the largest operating city hall in the U.S. Almost 700 rooms house three branches of government – the mayor’s office, the city council and a number of First District courts. And, arguably, it is the finest example of French Second Empire architecture and sculptural ornamentation in the country; the tower, portal entries and vast marble and granite facades are adorned with more than 250 monumental marble and bronze sculptures and motifs by Alexander Milne Calder, depicting commerce, trades, agriculture, science, mechanics, industry, justice and more.

Philadelphia City Hall was designed by Scottish architect John McArthur Jr. and built between 1871 and 1901 at the center of the city grid at Market and Broad Streets. By the time of its completion, the building had been surpassed in height by the Washington Monument and the Eiffel Tower. However, it remained the tallest building in Philadelphia until 1987, when One Liberty Place broke the terms of a "gentleman’s agreement" that no structure would rise above the city hall’s statue of city founder William Penn. At 37 ft., this 27-ton bronze statue, atop a 50-story clock tower featuring 26-ft.-dia. clock faces on all four sides, remains the tallest to crown any building in the world.

As the scaffolding came down at City Hall – located at the center of the city grid at Broad and Market Streets – its white
marble exterior was slowly revealed. It was the first time the city had seen the building this way, as nearby coal-burning factories and furnaces and railroads had turned the exterior dark gray and black shortly after its construction.

"The materials were the finest – marble, granite, bronze, sandstone, glazed Minton tile and cast iron," says Michael Holleman, AIA, director of historic preservation and principal at VITETTA, a Philadelphia-based multidisciplinary historic preservation studio. "The quality of the construction was the best possible, there has been relatively little work completed on the building in over 100 years, the materials selected provided fireproof construction, and every office and assembly space had abundant ventilation and light. It was a state-of-the-art building when it was completed. If completed today, these aspects of daylighting, natural ventilation and individual controls for each occupant at Philadelphia City Hall would be considered ‘green design.’ "

While Philadelphia City Hall has always been commanding, Philadelphians until recently were not able to fully appreciate the beauty and craftsmanship of its white marble exterior. Owing to the three major railroad stations that were within a stone’s throw of the building and the coal-burning factories and furnaces that engulfed the city in soot day and night, portions of the building turned dark gray and even black shortly after construction. Subsequent cleaning attempts had not revived the brilliant whites and vivid veining of the marble, instead turning the stone a grey and dull putty color.

VITETTA’s lead restoration architect, Nan Gutterman, AIA, and principal Hyman Myers, FAIA – in association with local firms Kelly/Maiello and Marianna Thomas Architects – have been turning the clock back at City Hall since 1999 through a three-phase exterior project. The mammoth undertaking included replacing the building’s flat roofs; stripping, restoring and repainting the cast-iron crestings on the mansards; repairing and repainting the wood windows and restoring and cleaning the stone facades, which Gutterman describes as "one of the best examples of the combination of art, decorative arts and architecture in the United States."

At 548 ft. tall, with foundation walls up to 24 ft. thick, the building is the tallest load-bearing masonry structure in the world.

Philadelphia City Hall was very nearly torn down in the 1960s and '70s, when "visionary" architects proposed building a replacement and leaving only the iconic tower. However, the historic preservation movement helped create a backlash, educating the public about the building and highlighting cost issues.

Following award-winning restorations of its North Portal and Conversation Hall, VITETTA was contracted by the city in 1992 to develop a master plan for the building, documenting its history and condition and a plan for its modernization, restoration and upkeep. And in 1998, the firm carried out further investigations following numerous roof leaks. These revealed that the building’s four-acre roof system, roof flashings and membranes had been so compromised that they were beyond patching, and significant leaks were occurring at the building’s monumental slate and cast-iron mansard roofs.

The exterior envelope project addressed these and other concerns through a mix of infrastructure and restoration improvements. Central to the plan were a number of demonstration projects and major reports and studies, which enabled VITETTA to refine its designs and specifications and meet the city’s tight budget. "It is such a vast scale – we’d worked on other large buildings, but this was big even by those standards – that it made us focus very carefully on the preservation treatments that would be applied over such great areas," says Holleman. ""We recognized that any ‘wrong decisions’ could be a calamity and cause irreversible damage. We completed significantly more material testing prior to the start of the work and worked with specialty disciplines like materials conservators on that testing."

Previous attempts to clean the stone facades had turned the marble grey and dull, and there were signs that it was deteriorating at a microscopic level.

The marble and granite testing was particularly extensive. It determined the safest and most effective way to clean the stone and pinpointed reasons for the delamination of the granite surface at the base of the building. "This type of study and testing went into every aspect of our work," says Myers, "from replacing gutters and roofing, to treating the rusted cast iron, to determining the best way to install a new sprinkler system." Water wash, low-pressure power wash, water misting, steam, detergent followed by power wash, laser cleaning, alkali chemical-cleaning systems and small-particle low-pressure air abrasion were tested. Cores were taken of test areas of each cleaning sample and reviewed in a laboratory, where a combination of misting and low-pressure air abrasion methods proved to yield the best results with the least material loss.

"We had found that one significant way the marble deteriorated was by ‘sugaring,’ which means that at a microscopic level the surface becomes rough and then powdery, losing cohesion," says Gutterman. "Continued exposure to rainwater further accelerates this type of deterioration, so a key criterion of the final cleaning method was its ability to create a smooth surface at the microscopic scale, along with a clean surface visually."

Extensive testing determined that the best way to clean the stone was with a combination of misting and low-pressure air abrasion methods.

Dan Lepore & Sons Company, a masonry contracting company based in Conshohocken, PA, carried out the cleaning of the marble facades, cutting out and repointing of masonry joints, patching and retooling and handling the stabilization work. However, VITETTA also employed the services of art conservators and geologists, four prime contractors, a host of subcontractors and general contractor Daniel J. Keating of Narberth, PA. And, as the building remained occupied throughout the work, the project became logistically complex.

"Working on an occupied building was definitely a challenge," says Gutterman. "Coordination with tenants, protection, schedule impact. We worked closely with the owner’s representative, C.B. Development, and made sure to coordinate with everyone by responding in a timely manner to all phone calls and emails and staying on top of any issues that arose."

The last portions of the scaffolding finally came down in November 2008, revealing a whiter, brighter Philadelphia City Hall. "As the building is situated on the intersection of Broad and Market Streets at the very center of Philadelphia, the restored facades positively shine," says Holleman, "reminding us what a great building it is and inviting the public to appreciate and understand the iconography behind the façade’s 250 sculptures."

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