Historic Concrete Is Made from Oyster ShellsEarly Atlantic coast settlers extracted lime from seashells to formulate concrete mix
These photos, submitted by Todd Rose of Todd Rose Concrete, Summerville, S.C., are of a chapel built in 1740 on St. Helena Island in South Carolina. The walls, still standing after more than two and a half centuries, are made of "tabby" concrete, an early form of concrete found almost exclusively on the southern Atlantic coast.
St. Helena Island is an historic site in Beaufort County and said to be one of the oldest settlements in the United States. The area also has the largest number of tabby structures in the country, built by early settlers in the coastal area using the abundant supply of oyster shells available to them.
"The process of making tabby concrete involves cooking oyster shells to create lime, which is then further processed to create a cementitious product," says Rose. "Also, there are no rocks in this part of South Carolina, so crushed oyster shells of various sizes are used as larger aggregate."
According to historical documents, tabby concrete was poured and tamped into wooden forms made of planks tied together. The boards were moved up as each layer of tabby concrete dried, until the desired wall height was reached. The imprint of the planks is often visible on tabby walls.
Today, an "artificial" type of tabby concrete is still made in the area and often used for driveways and walkways. "We often finish concrete in the coastal areas with an oyster-shell finish. It's like exposed aggregate, but we use the shells," says Rose.
For more information about the history of tabby concrete, see this reference from the Beaufort County Library.
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