Tabby

Tabby is a type of concrete, being a mixture of lime with crushed oyster shells, sand, gravel, or stones, and water, which when dry becomes hard. It was primarily made and used on the Sea Islands of coastal South Carolina, Georgia, and northern Florida in the Southern United States during the Colonial Period up until the early 1800s as a substitute for bricks in walling, which were rare and expensive because of the absence of local clay. The name comes from the Spanish word, tapia, which means "mud wall".

General

 * Origins and historical diffusion: North Africa, Canary Islands, North America (British, Spanish), and rammed earth construction.
 * Spatial distribution: Southeastern coast (South Carolina, Georgia, Florida), Texas, Caribbean, African; and technology transfer.
 * Local traditions: Eastern United States coast and Caribbean Africa; British and Spanish; Georgia, Florida, and South Carolina.
 * Building types: residential, military, outbuildings, commercial, industrial;
 * Construction methods: slip form; the mixture is placed between form boards, which are held together with wood form and wedges; the tabby mixture was rammed or tamped into place to fill the form properly, without voids; the construction of a wall proceeded upward in twelve-inch lifts in a fashion similar to a slip-formed, cast-in-place concrete wall.
 * Use: walls; structural components; tie system to roof, floor, and other components, foundations, floors and roofs, other (such as cisterns, benches, stairways).

Technical

 * Compressive strength: 250-1,000 psi
 * Absorption: 84.58
 * Specific gravity: 2.013
 * Formula: 1:3:1 lime:sand:shell with wood ash

Stabilization
The most appropriate stabilization for a tabby wall should be the same as any historic brick masonry wall suffering damage. Traditional repairs are the most direct, using similar technology to that available to the original builder. Walls function best when they are braced by floors and roofs. Protecting a tabby structure from moisture should be the primary goal.