NPS Uses Laser Technology to Clean Exterior Marble Surfaces at the Thomas Jefferson Memorial Using Great American Outdoo

Architectural conservators apply steam to the terrace wall of the Jefferson Memorial as part of the GAOA-funded cleaning of the memorial. NPS photo

The National Park Service used Great American Outdoors Act (GAOA) funding to clean exterior marble surfaces of the Thomas Jefferson Memorial, removing accumulated biofilm from the front steps; the steep, marble steps at the base of the memorial; and the terrace wall that encircles the memorial.

Situated on the Tidal Basin, the memorial is one of the most iconic structures in Washington, DC. The circular, open-air structure that honors Thomas Jefferson is constructed of white Imperial Danby marble from Vermont and features a signature dome supported by a circular colonnade.

Biofilm, a microbial community of algae, fungi and bacteria, was first noticed in areas of the memorial’s white marble in 2006 and became more pronounced in following years. In consultation with microbiologists, the National Park Service studied the growth starting in 2014 to determine the best treatment options.

The cleaning used a specialized process involving steam cleaning and lasers to remove the biofilm. Chemical cleaning could not be used due to the potential of runoff into the adjacent Tidal Basin. Laser ablation also ensured protection of the monument. By fine-tuning the laser settings to the specific stone and soiling types, it removed the biofilm without damaging the memorial’s historic marble.

The GAOA funding also allowed the park to make masonry repairs to weathered stone, repair cracks, and repoint or replace mortar joints. The project leveraged an existing construction project that replaced the memorial’s three roof systems and cleaned the biofilm from the dome.

What are the Benefits:

After years of deteriorating appearance caused by the spread of the biofilm, the GAOA-funded cleaning of the marble surfaces has restored the gleaming white appearance of the Jefferson Memorial that visitors to the National Mall expect, and that Thomase Jefferson deserves.

Where this belongs

• National Mall and Memorial Parks

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