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Foundation Issues with Your House

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Monday, September 16, 2019 - 7:00am

Announcer: Farm and Family is a production of the Mississippi State University Extension Service.

Amy Myers: Today we're talking about foundation issues with your house. Hello, I'm Amy Myers, and welcome to Farm and Family.

Today we're speaking with Dr. Larry Oldham, Mississippi State University Extension soil specialist.

Dr. Oldham, why do we have more foundation issues with some soils here in Mississippi rather than others?

Larry Oldham: Well, Amy, we're in Mississippi and our soils are highly variable, and they contain a lot of clays, and they contain a large percentage clays. I say a lot of clays saying that there are many different types of clay and we have a lot of house foundation issues in this state because of the clay content.

Clays can absorb many times their original size in water because of their makeup and their chemistry. Not all clays are equal in their ability to absorb water. Some soils which are more weathered, maybe a little bit older, are going to be predominated by one-to-one clays, which is a result of the fact that they are older, but it refers to the layered structure that they are. If you look at a clay microscopically, it's just layers of molecules, layers of atoms stacked on top of each other. And there's a one-to-one relationship in these one-to-one clays of the different type of layers.

On the other hand, many clays that we have in the state of Mississippi are two-to-one and these clays have a phenomenal ability to absorb water. These clays can absorb up to 200 times their own size in water. Some of the clay we have in this state, our famous Yazoo clay, actually can absorb much more water than 200 times. I've seen reports up to 600 times its own size in water.

Well, it absorbs the water. What happens then? Because the water takes up space, it fills up with water. The water fills up the space. The soil swells. Then, because we're in Mississippi, our climate changes. We get less rainfall and the soil starts to dry out. What happens then? Again, this is a three dimensional unit on a landscape. The water evaporates, drains away, the soil contracts. And every one of us has seen this on a small scale, because what happens when it gets dry? The soil cracks.

On a large scale, when we have something like a house or a highway, a factory building, anything built upon these soils, there can be a powerful force that moves that foundation. So all this goes back to the water and clay relationship.

Amy Myers: Okay, so not all clay is bad.

Larry Oldham: Yeah, not all clay is bad. It's just that we have to deal with what we've got. And I'm going to say that if you want to avoid foundation troubles, let's start at the beginning. Before you build a structure, before you do any sort of construction, learn about soil that you have on the location that you're dealing with.

You can start with a general look-over by using what's called the web soil survey on the internet. It's available through the Natural Resource Conservation Service, a unit of the United States Department of Agriculture. With the web soil survey, you can go to your specific location, and you can look at the soil properties and get some indications of what the management may require based upon those properties.

Amy Myers: Okay. So the best thing to do is first make sure that our house is built on a good type of clay. Is there a good type of clay?

Larry Oldham: Well, you're going to have to deal with what you have. So you get a first cut of what you're dealing with by looking at the soil survey. But then if it's going to be a significant investment, I encourage you or your builder to employ a soil technical engineering firm to do borings and see what you're actually dealing with on location. They might be able to go down to depths that they didn't evaluate with soil survey to see where the problem may be.

I know in many locations, particularly in the central part of the state where we have large deposit of the Yazoo clay or other of these super swelling clays, they do a lot of excavation before they build and then you replace it with a good clay, with a non-expansive type of clay.

Amy Myers: Okay. So a soil technical engineer is who we need to talk to if we have questions.

Larry Oldham: Yes. To find ones that are working in your area, you can start by checking with your local extension office or local office of the Natural Resource Conservation Service in the USDA Service Centers.

Amy Myers: So that's Mississippi State University Extension, right?

Larry Oldham: Yes.

Amy Myers: Today we've been speaking with Dr. Larry Oldham, soil specialist. I'm Amy Myers, and this has been Farm and Family. Have a great day.

Announcer: Farm and Family is a production of the Mississippi State University Extension Service.

Department: Plant and Soil Sciences

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