Thomas Jefferson Memorial

Washington, DC

Details: Laser & steam cleaning; Masonry stabilization & new roofing system; Accessibility upgrades; Exhibits

Owner: National Park Service, National Mall & Memorial Parks

Services: Cost Estimating, Full Design Services, Construction Administration, Building Information Modeling

After a 10-year period during which a dark biofilm grew on the dome of the Thomas Jefferson Memorial, the exterior has now been returned to its original gleaming white appearance through a series of restorations and repairs. In addition, the structure has a new, watertight roofing system and stabilized masonry. With a widely varied set of existing conditions to address, the design team developed full construction documents to replace more than 10,000 square feet of non-historic roofing at the flat roofs; remove, clean, and reinstall the marble portico roof tiles over new waterproofing; stabilize, repair, and clean over 30,000 square feet of marble elements including the dome, parapets, and entablature; clean and stabilize the limestone at the portico and colonnade ceilings; and install new drainage systems at roofs to prevent future water damage.

Conservation techniques specified included laser cleaning for the removal of biofilm, microabrasion for staining at the marble, blind pin repairs to stabilize cracked masonry, and replication of historic limestone ceiling elements where compromised units were removed at the portico. General construction activities included removal of tar waterproofing over the concrete substrate at the portico roof, installation of liquid-applied roofing membrane, installation of a membrane roof over tapered insulation at the flat roofs, repair of existing drains, installation of new drains, repair of the lightning protection system, and installation of new security features.

Laser cleaning is a new and highly specialized process that requires extreme safety measures (certification of each laser operator, fully enclosed, non-visually permeable enclosure, special goggles for the operator, and temperature monitoring). If it is not done properly, it can etch or burn the marble. Other types of staining/soiling required additional specialized conservation techniques like microabrasion.

Steam cleaning was used to enhance and improve the efficiency of laser ablation. Multiple tests were performed to determine the appropriate calibrations for the steam cleaning equipment to ensure effectiveness without causing damage to the marble. Ultimately steam cleaning was incorporated into the process prior to laser ablation as well as post laser ablation.

Subsequent phases of work include removing all barriers to access and improving the visitor experience at the memorial by following universal design principles to advance both physical and programmatic accessibility throughout the site while considering implications to the historic cultural landscape. On the exterior, two new sloped walkways east and west of the front steps will shorten the accessible route from the front of the memorial to the chamber level. Additionally, replacing the existing elevator will provide more reliable access from the ground level to the chamber. Inside, a full renovation of the memorial’s lower level will transform the visitor experience with improved circulation, an expanded gift shop, and enhanced visitor support spaces. New and expanded barrier-free, fully accessible exhibits within the lower level will provide additional perspectives on Thomas Jefferson’s multi-faceted story. New exhibits at the chamber level will share information about the history of the memorial itself with visitors.