For Release September 19, 2000
Of Foundations, Drought and Soils
by Chuck Otte, Geary County Extension Agent
Droughts are responsible for many strange and interesting things. Plants respond strangely to the hot dry weather, as do insects and animals. As the dry weather continues and the ground dries out, even soils will do strange things, including shrinking away from building foundations leaving large gaping chasms. Weíll get back to those large cracks in a little bit, but letís talk about the soil first.
Soil is composed of three basic elements: sand, silt and clay. The proportion of each of these components, gives each soil its characteristic. There are loams, and silty clays and sandy loams and a dozen others. The most active, of the three soil components, is clay.
Clay, more than the other two for our soils, dictate fertility, plant growth, water infiltration rates and water holding capacity. Many of our soils are very high in clay. A little clay goes a long ways, and even moderate amounts of clay can cause a lot of unusual things to happen.
One of the physical characteristics of soil is called shrink-swell potential. To help you understand the basic shrink swell concept, think of a kitchen sponge. When it is dry it is shrunken down. When you get it wet, it is much plumper and slightly larger. Clay is like this. The physical reason is somewhat complex and has to do with clay particles being very small, and the space between the particls and electromagnetic charges, among other things. To make matters even more complex, there is more than one type of clay mineral. Some have very high shrink swell, some very low. The common clays, locally, have very high shrink swell potential.
Walk out into your yard, garden or any field right now, and you will probably see cracks in the soil. Lots of cracks and some of them are quite big. This soil is very dry and it has shrunken down a lot. Some of these cracks are also quite deep, easily extending down a foot or more. This periodic drying and cracking is important to help break up soil compaction, but thatís another story. Once it starts to rain again, these cracks will slowly close back up as the soil slowly soaks up the water and expands back to itís original size.
Keep in mind that we build houses on these soils. When we head into these dry spells, the soils around our houses dry out and shrink. As they do, the foundations will start to shift and settle a little bit. Doors and locks may slowly start to stick or become difficult to work. Cracks may show up in foundations, plaster walls or drywall joints. Often, after we return to normal rainfall, the sticking doors will fix themselves. These are usually temporary nuisances.
Another common problem is that the soil will pull away from the foundation as it dries and shrinks. After a couple months of limited rainfall, you can find that you have a gap over an inch wide between your foundation and the soil. For many homeowners, the natural inclination is to get some dirt and fill this in. Thatís a big mistake! Once it starts to rain, the soil would swell back to itís original size. The soil you filled the crack with would be trapped and the swelling soil would put pressure against your foundation causing it to crack.
A better approach would be to start slowly soaking the soil. It took a couple of months to get this dried out, it isnít going to become re-wetted in one day. Lay a hose at a slow trickle (or better yet, a black spongy soaker hose), out away from the foundation a foot or two. Make sure that no water will run down the crack by the house. This is a quick way to find every crack in your foundation. Run it for a few hours, then move it somewhere else. After a few days you can come back to the same spot and wet it again. The soil will slowly start to get soaked up and will swell back to itís original size. I would also make sure that you have extensions on all your down spouts, so when it does start to rain, you get that water away from your foundation.
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