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Florida Geological Survey - Florida Hazards: Problem Soils
cracking clays

Most clay minerals are hygroscopic, meaning they have a tendancy to absorb moisture. As the water table naturally fluctuates with local precipitation, the soil beneath a home or other building may shrink or swell depending on the amount of clay within it. If the soil contains a large amount of expansive clays, damage may occur to the stucture, especially in times of heavy rainfall or drought.

The most expansive clays (also referred to as "pipe clay") include the smectite group of clay minerals. Smectite is common throughout the Hawthorn Group, a geological layer that lies beneath much of Florida. The chemistry of the water that comes in contact with smectite may contribute to the shrinking or swelling effect. Contractors may recommend soil tests for various types of problem soils including pipe clay before foundation design is finalized.

Organic matter is extremely common in subsurface sediments of Florida. The organic matter is formed from the remains of wetland plants that were deposited over hundreds of years. These deposits can be covered by other types of soils so they can’t be seen at the surface. When organic matter is exposed to air it may become oxidized and slowly destroyed. It may also lose volume or shrink due to compaction. Slow sinking or subsidence results from these processes and it has the potential to cause foundation and structural damage.

Major signs of foundation damage and problem soils include cracking in walls or moldings, uneven floors, and sticky doors and windows. Damage such as cracking of foundations and other structural problems can also be caused by sinkholes and subsurface voids as well as problem soils. When this type of damage occurs, homeowners are advised to contact their insurance companies. Various tests can be performed to determine the cause of the damage.

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Last updated: November 10, 2014

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