What is Tabby, you ask?

Tabby is a type of concrete made by burning oyster shells to create lime, then mixing it with water, sand, ash and broken oyster shells. Early Spanish settlers in present-day North Carolina and Florida used the substance for building purposes. British colonists primarily in coastal South Carolina and Georgia used it as well.
Revivals in the use of tabby spread northward and continued into the early 19th century. A coating of plaster or stucco normally protects the material.
Tabby’s origin is uncertain.
Evidence exists that North African Moors brought a predecessor form of the material to Spain when they invaded that kingdom. Morocco uses a form of this substance to this day. Some tabby structures survive in Spain. In both instances the aggregate is granite, not oyster shells.
It is likely that 16th-century Spanish explorers first brought it (which appears as “tabee”, “tapis”, “tappy” and “tapia” in early documents) to the coast of Florida in the sixteenth century. Tapia is Spanish for “mud wall.” Arabic tabbi means a mixture of mortar and lime or African tabi. In fact, the mortar chinks the earliest cabins in this area. Arabic tabbi uses a mixture of mud and Spanish moss.
The oldest known example of Tabby concrete in North America is the Spanish Fort San Antón de Carlos. Fort San Antón de Carlos is located on Mound Key in Florida. St. Simons Island settlers used tabby for building such plantations as Canon’s Point Preserve.
Some researchers believe that English colonists developed their own process independently of the Spanish.
James Oglethorpe is credited with introducing “Oglethorpe tabby” into Georgia after seeing Spanish forts in Florida and encouraging its use, using it himself for his house near Fort Frederica. Later Thomas Spalding grew up in Oglethorpe’s house. He led a tabby revival in the second quarter of the 19th century sometimes referred to as “Spalding tabby”. Another revival occurred with the development of St. Simons Island and Jekyll Island in the 1880s.
Source: https://en.wikipedia.org/wiki/Tabby_concrete