Talking about expansive soils is a dirty job, but somebody's got to do it. It's important to learn about expansive soil because it affects house structure in areas that are high in this type of soil content.

Regions that were once primarily flooded plains or places with lakes that long ago dried up contain high amounts of expansive soils. Much of the soil content in these areas contains finely grained clay or clay minerals, which sucks up any water that's nearby like a monster sponge. Of course, there are many other areas besides drained lakes that contain these soil mixtures. Hillsides are also guilty of holding on to this type of dirt.

Expansive soil experiences huge changes in volume depending on moisture content at a given time. A small mound of this clay-dirt can double in size from just a very little addition of water. Then it dries up and shrinks back down.

You can look for visible signs of expansive soil, but you can't just judge by what you see on the ground. Sometimes it's covered by layers of topsoil and the area's natural vegetation. And when it dries out and the volume decreases, cracks occur.

Some soils have a popcorn-like appearance. You also have to look for excessive surface cracks. Both of these characteristics occur because the soil gets wet and then dries, and this repeats over and over again. You can also tell because soil that contains high amounts of clay minerals is usually pretty sticky when wet.

If you're looking for a home, be aware of these warning signs, visible in constructed areas:

Many cracks along a foundation.
Multiple cracks running through a driveway.
Undulating waves on the street surface.
Cracks that run up the side of a building.
Window panes that bulge or don't seem to fit correctly.


You should ask your real estate agent if property that you're considering is in an area known to have expansive soils. In some parts of the country, the government mandates testing. You can also look in your local phone book in the government directory pages-these are often called the blue pages-for your State Geological Survey or Geological Department. Someone in that office can tell you if there is high expansive soil content in your area.

Many beautiful places are covered with these soils. Parts of North and South Dakota, California, Montana, Texas, Arizona, and Colorado-just to name a few-are affected. There are measures you can take to protect your property:


Whenever rain falls, clear your property of any pooled water as soon as possible.
Keep rainspouts and gutters at peak functioning. Be certain they discharge water onto concrete walkways and not into the ground near your house's foundation.
Consider hiring a contractor to grade your property for better natural drainage.
Avoid planting trees near your house, because the roots attract water.
Maintain your lawn's moisture at a uniform level all year long, but don't over-water it.
Do keep the lawn and the area around the house slightly damp so that the characteristic drying and cracking does not occur.
Consult a soil engineer before you install a patio or garden wall, because they can trap waters and keep them from draining.