William Penn is due for a physical.

Not to mention a waxing and a buffing.

The City of Philadelphia plans to restore Penn's bronze statue atop City Hall in late August. The work will take three to four weeks, during which time the observation deck will be closed.

Penn's statue was last restored in 2007 with funds from the Preservation Alliance for Greater Philadelphia and the city. This time, a different mix is involved: $125,000 in private funds, a $25,000 National Endowment of the Arts (NEA) grant, and $100,000 of city money, said Margot Berg, the city's public art director.

"We think of this sculpture as sort of the iconic piece in the city," Berg said. "It's very symbolic for Philadelphia, and it's important for us to maintain so visitors and residents for generations to come are able to enjoy seeing the piece and visiting the observation deck and looking up at him."

The statue was created in 1892 by the sculptor Alexander Milne Calder, who studied at the Pennsylvania Academy of the Fine Arts and who spent nearly 20 years creating about 250 figures for City Hall.

Berg said the 124-year-old statue needs restoration about once a decade. The city didn't learn that lesson until the 1980s, when Penn - green from corrosion and acid rain - was first treated. He was treated again in 1996 and then in 2007, all three times by Moorland Studios of Stockton, N.J.

The conservators said environmental exposure had compromised the protective coating on his back and shoulders when they last examined him, in 2007. Corrosion had begun to make its way into his hat's brim and crown, as well as the tree stump sculpted at his side.

"It is impressive proof of 1892 craftsmanship that the 37-foot Penn statue, fitted together in 47 sections with 1,402 bolts, has withstood numerous direct lightning strikes, hurricane-force winds, and all the man-made chemistry of an urban environment," the conservators, Constance K. Bassett and David Cann, said in an email.

The statue is to be washed with detergent and scrubbed with brushes. After 10 years of dirt is removed, conservators will closely inspect the bronze - which after all this time is very porous, Berg explained. Making patch-ups where corrosion occurred, conservators will then apply a corrosion inhibitor and rub a wax coating all over. After a good buff, the work is done.

The task involves high-melting-point wax, conservation soap, more than 1,000 gallons of deionized water, and a crate of brushes - on scaffolding 500 feet up. Scaffolding and insurance are the big costs, Berg said.

The Office of Arts, Culture and the Creative Economy plans to share images and updates of the work via social media and a film and photo gallery in City Hall.

The NEA announced Tuesday that Philadelphia had won the $25,000 grant to put toward the restoration. More than a dozen arts groups in Philadelphia were awarded a combined $800,000 of $82 million the NEA distributed to projects across the country.

Kelly Lee, the city's chief cultural officer, noted that Philadelphia maintains 1,100 pieces of public art citywide. "But this," she said, "is our crème de la crème."