The Commission of Fine Arts repeatedly urged the architects to use bronze for the scrim, as it created a "shimmering, lustrous effect under many lighting conditions" and "conveyed dignity, permanence and beauty". Duranar paint was the first substitute proposed by the architects, but the commission members rejected it, noting that it had a "putty-like appearance under overcast conditions" and visually fell "far short of the beautiful poetic intention promised by the concept design". A second finish, the sprayable metal LuminOre, was rejected by the commission because it was difficult to produce in the high quality needed, and was prone to flaking and discoloration. Electroless plating and anodized aluminum were rejected because they lacked durability. A physical vapor deposition process involving a nickel-chrome plating was dismissed for not achieving the right color, luster, or warmth. In early 2014, tests were made with polyvinyl difluoride (PVDF). This coating was approved by the Commission of Fine Arts on February 20, 2014, and by the National Capital Planning Commission in April 2014. Construction of the museum building The museum's groundbreaking ceremony took place on February 22, 2012. President Barack Obama and museum director Bunch were among the speakers at the ceremony. Actress Phylicia Rashād was the Master of Ceremonies for the event, which also featured poetry and music performed by Denyce Graves, Thomas Hampson, and the Heritage Signature Chorale. Clark Construction Group, Smoot Construction, and H.J. Russell & Company won the contract to build the museum. The architectural firm of McKissack & McKissack (which was the first African American-owned architectural firm in the United States) provided project management services on behalf of the Smithsonian, and acted as liaison between the Smithsonian and public utilities and D.C. government agencies. Guy Nordenson and Associates and Robert Silman Associates were the structural engineers for the project. The NMAAHC became the deepest museum on the National Mall. Excavators dug below grade to lay the foundations, although the building itself will be only deep. The museum is located at a low point on the Mall, and groundwater puts on the walls. To compensate, per minute of water were pumped out every day during construction of the foundation and below-grade walls, and a slurry of cement and sand injected into forms to stabilize the site. Lasers continually monitored the walls during construction for any signs of bulging or movement. The first concrete for the foundations was poured in November 2012.