U.S. Capitol Stone and Metal Preservation, North Extension
Washington, D.C.
Award of Merit

Owner: Architect of the Capitol
Lead Design Firm: Mary Oehrlein and Associates
General Contractor/Construction Manager: Grunley Construction Co.
Subcontractors: Robinson Iron Corp. (Metals Restoration); Conservation Solutions Inc. (Bronze and Metal Conservation; Laser Cleaning (Pediment Sculpture and Stone Conservation); Lorton Stone (Facade Cleaning and Restoration); Aeon Preservation Services; Crenshaw Lighting (Light Fixture Restoration)

The project team says that preserving the U.S. Capitol’s ornate facade involved “firsts” in the nation for the successful execution of large-scale laser ablation cleaning and stone consolidation to conserve a marble exterior.

A preservation task that Congress funds only once every 60 years, the $15.5-million project required preserving historic stone masonry and metal elements using high-tech processes rarely performed under a tight construction schedule, the team says.

The nearly 36-month project included: delicate laser ablation cleaning and consolidating of 50 portico Corinthian columns and capitals; restoration of all 98 terrace lamp posts; 25 bronze hanging pendant lights; and six large lampposts on the Capitol’s east facade. Off site, 28 handrails and guardrails also were restored and reinstalled.

Laser ablation helped remove gypsum crusts from the marble exterior before the team implemented a masonry technique called consolidation, which binds microscopic loose marble grains back together and restrengthens it. That work has served as a proving ground for future preservation efforts, the team says.

Scheduling, accessing work areas and security were complicated by the presence of the millions of guests who visit the Capitol each year. That required the team to remain flexible, including complying with frequent changes to security protocol, often without advance notice, while staying on schedule.

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