One thing professional contractors learn is how the type of soil affects concrete installation. Depending on the type, it can make concrete installation easier, harder or even unfeasible. Soil can be sandy, clayey or loamy, and there are a surprising number of subtypes.
How you can tell what type of soil you have
If you want to know what type of soil you have, one way is to wet a handful of soil and squeeze it. Sandy soil crumbles apart, clay soil holds its shape, and loamy soil is somewhere in between. You can also check a soil map. These maps are easy to find online. Check with the Natural Resources Conservation Service (NRCS), your local county or the U.S. Department of Agriculture (USDA). Local builders are likely to know what type of soil is in your area and how it can affect concrete installation.
Loamy soil
Loamy soil, which is good for plants, is also a good base for concrete. It’s made of sand, clay and silt. This combination makes loamy soil firm yet well-draining.
Silty soil
This type of soil is fine and slippery, so it doesn’t hold together well. If you install concrete over silty soil, it might be unstable.
Sandy soil
Sandy soil drains beautifully, but it’s crumbly and won’t hold its shape. As with silty soil, concrete installed over sandy soil can become unstable over time.
Clay soil
Clay soil is famously heavy and not very good for concrete installation. It holds water for a long time and doesn’t allow it to drain. When it’s dry, it shrinks and cracks. This not only makes a concrete slab unstable but can also cause it to crack or spall.
Gravel soil
This type of soil is made up of bits and pieces of rocks. This allows it to drain effectively and remain stable. Gravel is often laid first before concrete is poured over it.
Chalk Soil
This soil is made from tiny particles of limestone. It’s basically what people use to write on blackboards. The problem with chalk is that it’s very alkaline, with a pH as high as 10. It drains well but can crumble when dry and grow unstable when it’s wet.
Peat soil
Peaty soil is the opposite of chalk soil in that it’s very acidic. It’s made of rotted plant matter and retains water. The organic material breaks down over time, forming black, tarry muck. The concrete laid over peaty soil eventually sinks.
The type of soil in your area impacts a construction project in surprising ways. If you want to learn more about this, check out our Marketplace, where you can find a licensed local professional to advise you. And be sure to visit our pages on Instagram and Facebook.
