South Extension - House of Representatives Wing

U.S. Capitol, Washington, D.C.
President George Washington laid the cornerstone for the original building on September 18, 1793, which has been greatly expanded over more than two centuries since. Marble mined from Lee, MA, and Cockeysville, MD were used in the mid-19th century expansion of the House South Extension.
EverGreene significantly contributed to the restoration of the South Extension of the US Capitol exterior stonework, which took place from 2018-2020. Our conservators performed laser cleaning and chemical consolidation on the carved marble cornice, columns, pilaster capitals, and window and door surrounds during a major exterior restoration of the Senate wing. After general cleaning (performed by others), we used two 100-watt and two 500-watt, Q-switched lasers operating at 1064 nm to ablate the remaining black sulfate crusts and soiling without damaging the weathered stone substrate. The laser effectively reduced black crusts and soiling on the marble, leaving a substantially cleaned surface. Chemical consolidation of friable stone followed to help slow the deterioration of the carved details.