South Extension - House of Representatives Wing

U.S. Capitol, Washington, D.C.
The cornerstone of the original House of Representatives was laid by President George Washington on September 18, 1793. Since then, the building has been greatly expanded over the past more than two centuries. Marble mined from Lee, MA, and Cockeysville, MD was used during the mid-19th century for several expansion initiatives.
During the restoration of the U.S. Capitol South Extension, which took place from 2018-2020, EverGreene’s conservators performed laser cleaning and chemical consolidation on the carved marble cornice, columns, pilaster capitals, and the window and door surrounds during a major exterior restoration of the Senate wing. After general cleaning, two 100-watt and two 500-watt, Q-switched lasers operating at 1064 nm were used to ablate the remaining black sulfate crusts and soiling without damaging the weathered stone substrate. The laser cleaning treatment effectively reduced buildup and staining on the marble, leaving a substantially brightened surface, free of harmful pollution residues. Chemical consolidation treatments of friable stone followed to help slow the deterioration of the historical carved marble details.