After more than a century of use, Philadelphia City Hall was overdue for a cosmetic facelift that included restoring exterior cast iron with a protective coating system from Tnemec to retain the integrity of this National Historic Landmark. “We had to go through a pretty extensive process for the off-white color to be approved,” according to Tnemec coating consultant Pat Murphy. “This is the most recognizable historic building in Philadelphia, so maintaining its architectural significance was a paramount consideration.”
The overall project was completed in phases over a three-year period, Murphy noted. “This is the busiest street in Philadelphia, so we had to scaffold the building and enclose the area that was being coated,” Murphy recalled. “The exterior cast iron was rusted, so it was cleaned by abrasive blasting. Whenever you’re abrasive blasting, you obviously can’t expose the public to dust, sand and paint.”
The architect specified a coating system that would provide long-lasting corrosion protection, acknowledged Tnemec coating consultant Ed Enoch. The specification called for a prime coat of Series 530 Omnithane, a moisture-cured aromatic polyurethane, followed by an intermediate coat of Series 66 Hi-Build Epoxoline, a polyamide epoxy, and a finish coat of Series 1075 Endura-Shield II, an aliphatic acrylic polyurethane. Enoch estimated more than 200 gallons of each coating were required for the overall project. “The applicator was very impressed with the extremely strong bond between the primer and the cast iron substrate,” Enoch reported. “The coating system covered extremely well.”
“Whenever we recommend high-performance coating systems for metal structures in Philadelphia, this building is mentioned because everyone in the city knows this familiar landmark,” Murphy added.
Built from 1871 to 1901, Philadelphia City Hall houses three branches of government, the Executive Branch, the Legislative Branch and the Judicial Branch’s Civil Courts. Many people come to see City Hall because of its history and architectural significance, but it is still a fully functioning municipal building. A National Historic Landmark, the building was also named a National Historic Civil Engineering Landmark by the American Society of Civil Engineers in 2006.