U.S. Capitol North Extension Senate Wing

As part of the comprehensive exterior restoration of the U.S. Capitol’s North (Senate) Extension, EverGreene conservators performed specialized marble conservation treatments to preserve the building’s richly carved architectural stonework between 2015 and 2017.

The United States Capitol, whose cornerstone was laid by President George Washington in 1793, has evolved over more than two centuries into one of the nation’s most recognizable civic landmarks. The mid-19th-century expansion added the Senate and House wings, constructed with marble from Cockeysville, Maryland, and Lee, Massachusetts, and enriched with finely carved columns, capitals, cornices, pediments, and ornamental architectural details that define the Capitol’s monumental appearance.

Working as part of the Architect of the Capitol’s restoration campaign, EverGreene’s scope mirrored that of the South Extension, focusing on the conservation of the Senate Wing’s carved marble elements. Treatments included the cornices, columns, pilaster capitals, and the decorative surrounds of windows and doors, all of which had experienced decades of weathering and the accumulation of damaging black sulfate crusts.

Following the general cleaning campaign performed by others, EverGreene employed advanced laser cleaning technology to selectively remove deeply embedded black crusts and atmospheric soiling while preserving the fragile, weathered marble surface beneath. Conservators carefully revealed the original character and fine sculptural details without the abrasion associated with conventional cleaning methods.

Following laser treatment, areas of deteriorated marble were strengthened through the application of chemical consolidants to stabilize friable stone and help slow future deterioration.