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The Copper and Slate Puzzle

At Mount Vernon, the Architecture and Archaeology teams often work together to solve puzzles.

While excavating the North Grove (in preparation for the Mansion Revitalization Project), archaeologists found a significant number of copper sheets and slate fragments. The slate fragment pictured above has a nail hole, which is characteristic of roofing slates. However, George Washington used wood shingles, not slate, on his buildings.

Washington purchased hundreds of thousands of wood shingles for Mount Vernon during his lifetime, most of them split from cypress trees cut in the Dismal Swamp of southern Virginia. (MVLA)
Washington purchased hundreds of thousands of wood shingles for Mount Vernon during his lifetime, most of them split from cypress trees cut in the Dismal Swamp of southern Virginia. (MVLA)

Washington purchased hundreds of thousands of wood shingles for Mount Vernon during his lifetime, most of them split from cypress trees cut in the Dismal Swamp of southern Virginia. (MVLA)

Learn More About Washington's Roof

 

Together, the teams determined that these copper and slate fragments are likely remnants of the termite proofing installed in the Mansion and outbuildings in the 1930s, which include copper termite shields and flat layers of slate.

Termite Proofing?

By the late 19th century, moisture and termites had damaged a number of framing elements at the first-floor level of the Mansion. Mount Vernon staff undertook localized repairs involving replacing wooden framing elements with brick and slate added to the top of the foundations. Sheet copper was inserted between the brick and slate and the remaining wood framing to act as shields preventing termites from reaching the wood.

Such repairs resolved the immediate problems but inadvertently impacted the integrity of the original structural system.

View of the 1932 installation of a copper termite shield above the Mansion foundation, with framing visible above the copper. Over the years, localized repairs, such as termite shields, resolved immediate problems but inadvertently impacted the integrity of the original structural system. (MVLA)

So, the copper and slate fragments discovered by the Archaeology team are part of a larger Mount Vernon story—a story that continues to unfold at this very moment. 

During the Mansion Revitalization Project, Preservation carpenters are addressing areas of the framing that were impacted by the installation of termite shields. They will replace non-original floor joists and sills and reconstitute the joinery between elements, enabling the structure to again function as intended by 18th-century carpenters.

Mansion Revitalization Blog

Follow along as we post updates and discoveries from the landmark Mansion Revitalization Project.

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