North Extension - Senate Wing

U.S. Capitol, Washington, D.C.

The United States Capitol houses the two branches of Congress, the House of Representatives on the South side of the building and the Senate on the North. On September 18, 1793, President George Washington laid the cornerstone for the original Capitol building, which has expanded tremendously over the last two plus centuries. Marbles from Cockeysville, MD and Lee, MA were used in the mid-19th century addition of the Senate Extension.

The scope for restoration of the North Extension of the U.S. Capitol exterior stonework was identical to that of the South Extension. Our conservators performed chemical consolidation and laser cleaning 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 one 500-watt, Q-switched lasers operating at 1064 nm to ablate 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 deterioration of the carved details. This work was completed from 2015–2017.