What is Expansive Clay Soil?

What is Expansive Clay Soil? How Does It Affect My Home’s Foundation?

You have heard people talk about clay, clay soil, or expansive clay soil but you don’t know what it is or why it’s important. You’re like, “Who cares what kind of soil we have? It’s all just dirt, isn’t it?”

As a curious and conscientious homeowner, you probably should care a little bit about the soil when it comes to your home’s foundation. In the US, expansive clay soils result in greater costs to property than all other natural disasters combined. 

That means that tornadoes, hurricanes, floods, and earthquakes together cause less financial damage for homeowners annually than expansive soils. Plus, typical foundation issues are not always covered by insurance.

Expansive clay soils affect all types of foundations in our Central Texas area, and not in a good way. Knowing more about this soil type will help in your understanding of foundation health, foundation settlement, foundation problems, and foundation repair. 

Anchor Foundation Repair

You might say that understanding how clay soils can impact homes is the *foundation* of foundations. I know . . . that’s a lot of foundations, but foundation “dad jokes” are basically required at this point.

At Anchor Foundation Repair, we care about expansive clay soils because they impact the work that we do repairing Brazos Valley foundations each year and for the past 35 years. Although we are not official soil experts or geotechnical engineers, we do understand how our soil properties can cause movement in your home’s foundation.

This article will review some soil basics, properties of expansive clay soils, how these soils affect home foundations, and what you can do about it. Let’s get started!

General Soil Facts

All soils (or dirt as most people like to call it) are made up of varying amounts of sand, silt, and clay. There are sandy loams, gravelly fine sandy loams, silty clays, loamy fine sand, clayey soils, and the list goes on . . . it’s almost comical to see all ways used to describe our dirt. 

Solutions for Brazos Valley Foundation Repair
Sandy Loam topsoil

You can find the soil description of any area of the United States on the Web Soil Survey maps provided by the USDA. It’s a pretty deep dive into details though so not everyone will want to go that granular (yes, the puns keep coming).

To save you the trouble of figuring out what we have here in Central Texas, it’s a lot of clay. Texas is dominated by the highest percentages of clay present in US soils as shown on this expansive soil map from Geology.com

How is Expansive Clay Soil Different from Other Soils?

Most ingredients in any soil do not react to moisture, except some clay minerals present in clay soils. Any clay mineral that reacts to water is considered to be “expansive.” A fairly common clay mineral present around these parts is called smectite and it is one of the expansive ones. 

To most people, knowing the names of all the clay minerals that expand is not super important (not even to us!). But what is important is understanding how expansive clay molecules behave in the presence and absence of moisture.

Expansive clay molecules are like a sponge that swells up when wet and gets smaller when dry. The wetter it gets, the bigger the molecules can expand. The drier and drier the clay soil gets the more it can contract and shrink. Clay can expand as much as 10% in size when exposed to prolonged moisture.

Bryan College Station Foundation Repair

Does Clay Soil Cause Foundation Problems?

Yes, clay soil can cause foundations to have problems. But before you have problems, you just have movement, also called foundation settlement. Clay that has a ten percent expansion rate can cause a lot of movement. Expanding soil under your home can have great effects on your foundation.

Imagine this, let’s say your home is built on top of many towers of ten bricks each (this is not a real home but work with me here on this hypothetical example). One side of your house gets really wet and the clay molecules expand under that part of your home the most, but not as much around the rest. 

Foundation Problems

Ten percent clay expansion is like shoving an 11th brick underneath part of your house. Now imagine that happening each year, every time it rains a lot.

But then what happens when it’s dry and there is no rain? Good question. The expansive clay will shrink. The drier it gets, the more it can shrink. It can even shrink further than when your home was originally built. 

So things dry out under your hypothetical home and that 11th brick is “removed” and you are back to the home’s original elevation. But let’s say it keeps getting drier and drier and we are in a drought. Then it’s almost like another brick (or part of one) getting taken away from under the house and you are down to 9 bricks.

This is a simple way to explain what is happening to a home built on expansive clay soils. The movement caused by clay expanding and contracting each year through our rainy and dry seasons can cause problems for your foundation. This is especially true in an area like Texas where sometimes it rains a lot, and then it gets super dry later on.

The slab-on-grade foundations and pier and beam foundations commonly found in our area would begin to show telltale signs of foundation settlement that could lead to problems that need to be repaired. This is a slow process that happens over many years, so you might see it coming but it is very gradual, not sudden.

Can I Avoid the Effects of Expansive Clay Soil on My Foundation?

There are three ways to avoid the effects of expansive clay soil on your foundation: 

  1. Move Out of Texas
  2. Try Prevention Techniques
  3. Add Foundation Underpinning

It’s more about minimizing and overcoming the effects than avoiding them, but let’s explore these minimization ideas real quick . . . 

1. Move Out of Texas and Go to Another State

Avoiding Expansive Clay Soils
You could always move . . . just kidding!

I’m just being silly here and am not actually suggesting that you move away. What I am really saying is that expansive clay is difficult to avoid where we live. So if it bothers you that much, you could certainly move but that might not be too practical for many reasons. 

Just remember that other areas have various issues you might have to deal with too, like those other natural disasters I mentioned earlier? Hurricanes, floods, tornadoes, earthquakes . . . and did we mention volcanoes before? Everywhere you go might have some kind of problem. Now expansive soil doesn’t sound so bad, does it?

2. Try Some Prevention Techniques

home foundation repair

You can always try to ward off the effects of expansive clay soils on your foundation. It may or may not work, there are no guarantees here. But if you want to check out our thoughts on this topic, we have this article for you, “Can I Prevent Foundation Problems in My Home? 3 Ways to Try.”

3. Add Foundation Underpinning aka Foundation Repair

Underpinning is an engineer’s way of saying, “adding support.” Foundation repair is the way to add that support. 

People don’t just automatically add underpinning support to their homes in expansive clay soil areas when a home is built or they first move in. Homeowners wait until there is an actual foundation problem with their homes, like doors that don’t close properly or big cracks that are embarrassing or letting in moisture.

Expansive Clay Soil is Not a Guaranteed Problem

Expansive Clay Soil causes foundation problems sometimes

A home built on expansive clay does not guarantee that you will have a problem, it’s just a problem that could come up that you might have to handle. Foundation repair is the way to minimize and control the effects of expansive clay soils as much as possible if they become an issue for you.

At Anchor Foundation Repair, we know *a thing or two* about foundation repair as well as foundation problems. It’s pretty much in our name. We have inspected and repaired thousands of Bryan, College Station, and Brazos Valley homes through two generations in the business. We have a lot more to tell you about foundation repair if you are interested. 

The next article you might want to check out is this deeper look into “Foundation Problems: Causes, Prevention, and the Decision to Repair.” Dig in and see what it’s all about starting from the ground up . . . just had to get in a couple more puns before I let you go . . . take care.