How can I tell whether my house foundation problems are caused by a sinkhole or expansive clay soil?

Friday, August 30, 2019

Because the crack patterns can be similar, it often requires an engineering evaluation of the soil under the home to find out what is causing the structural distress in your walls. Soil boring samples and ground-penetrating radar are two tools used make a determination.

    But there is one generalization that might point you in the right direction. Sinkholes increase during times of extremely wet weather—such as after a hurricane or series of thunderstorms—because they are caused by water dissolving the karst rock layer beneath the soil overlay, but clay soil problems are the worst during periods of drought. 

    Clay soil expands when the moisture in the soil increases, and shrinks when it dries out; yet the problems tend to be more pronounced when the soil drops during a prolonged drought. During one drought in our area a little over a decade ago, wells went dry and soil subsidence induced by clay soil was at its worst. 


    Also, sinkhole problems tend to be an event that happens over a short period of time. The up-and-down movements of clay soil, although smaller, are cumulative and crack up the walls of a house gradually over time. So houses more than about 10 years old are very likely to show signs of movement of clay soil below, if it is there, but a sinkhole can appear at any time. 


    Many sinkholes are not the house-swallowing variety that make the news. The house is not at the bottom of a big hole, but walls are severely fractured, while sunken areas and pits in the ground around the home indicate the sinkhole activity. 

    Clay soil is easily recognized by the crack patterns in the surface that occurs when it dries out, like in the photo at the top of the page. Florida, unfortunately, has much of its clay soils buried in veins below the sandy soil on top. The Hawthorne Formation, a geologic layer which underlays some parts of the state, is one example.


 Clay Soil Damage Not Covered By Insurance

   Whether the structural damage to a home is caused by a sinkhole or clay soil is often a point of contention with insurance companies. Clay soil is considered an existing condition, and not covered, while a sinkhole is covered. And there can be differing options between engineering firms hired to assess the situation as to which one it is. 

    Also, see our blog post How can I avoid buying a house with clay soil heaving foundation problems?

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To learn more about exterior walls and structures, see these other blog posts:

 What is the average lifespan of a house foundation?

 What causes vertical cracks in fiber cement siding planks?

 • What causes raised white lines of residue on a block wall that are crusty and crumbling? 

 What is the difference between soil subsidence, heave, creep, and settlement? 

 How much ventilation is required for the under-floor crawl space of a home? 

 What causes stair-step cracks in a block or brick wall?

 What causes a horizontal crack in a block or brick wall? 

 How can I tell if a diagonal crack in drywall at the corner of a window or door indicates a structural problem?

 What causes the surface of old bricks to erode away into sandy powder? 

 What are the pros and cons of concrete block versus wood frame construction?

 Should I buy a house with a crawl space? 

 Why is my stucco cracking?

 There's cracks running along the home's concrete tie beam. What's wrong? 

 What would cause long horizontal lines of brick mortar to fall out?

 How do I recognize structural problems in a retaining wall? 

 What is engineered wood siding?

 Should I buy a house that has had foundation repair? 

 What is a "continuous load path”?

• Should I buy a house with sloping floors? 

 Should I buy a house with asbestos siding?   

 How can I tell if cracks in the garage floor are a problem or not? 

 What do you look for when inspecting vinyl siding?

 Why is housewrap installed on exterior walls under the siding? 

 How do I recognize serious structural problems in a house?

 Why did so many concrete block homes collapse in Mexico Beach during Hurricane Michael? 

 How can I tell if the concrete block walls of my house have vertical steel and concrete reinforcement?

 Should I buy a house with structural problems? 

 What are those powdery white areas on my brick walls?

 What causes cracks in the walls and floors of a house?

 How can I tell if the exterior walls of a house are concrete block (CBS) or wood or brick?

 What are the common problems of different types of house foundations? 

• What are the warning signs of a dangerous deck?

       Visit our EXTERIOR WALLS AND STRUCTURE page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles. 

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