The Oyster Shell

by Jonathan BrisendineField Archaeologist

As part of the ongoing project of the Old Colchester Park and Preserve, the CART team has located several foundations to historic buildings of various types of construction material. These foundations range from crafted brick to dry laid plain slate stones. Now you may ask what does this have to do with oysters. While most people think of the oyster as an aphrodisiac, most will be surprised that in the past its shell was also used as a key ingredient in mortar. This type of mortar is called Tabby which is made by burning the oyster shell to create lime. Lime at the time was expensive and hard to acquire. The burnt shell was then combined with water, sand, ash, and other broken oyster shell fragments. Seen here is an example of this type of mortar holding a brick foundation together.


Oysters serve a dual purpose. While needed as a key ingredient to make mortar they also served as a cheap and readily available source of nutrition, found locally in the Occoquan and Potomac Rivers. Because of this it was highly popular to use tabby in the majority of buildings as just like in todays’ society the working class made up the majority of the population. Massive oyster beds can be found throughout the coastal region. It’s thanks to this wonderful creature that many of the remnants of the long forgotten structures that we find survive the test of time intact.

So here is to the oyster, not only are you delicious but you also help preserve the past for future generations to enjoy as well as acting as a natural filter to help keep our waterways clean.


To see a close up example of shell in mortar go to



About cartarchaeology

We are the County Archaeological Research Team, part of the Archaeology and Collections Branch, Resource Management Division, Fairfax County Park Authority. We are tasked with understanding and managing the cultural resources on Park land throughout Fairfax County.
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