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Clay Soil

Clay is an expansive type of soil and is highly likely to cause your foundation to sink when it dries up.

Soil is a natural resource that can be categorized into different soil types. Each of these soil types has its characteristics, which determine its strength and stability. Knowing as much as you can about the soil on your property is critical in building a stable foundation. If you plan on building your home in an area with predominantly clay soil, here is everything you need to know. 

What Is Clay Soil? 

Clay is a type of soil with fine grains, less pore space, and minimal amounts of organic material. It remains wet and cold in winter and dry and light in summer. Due to its particle size, clay soil drains water slowly and takes longer to warm up in summer. Its slow drainage means that most of the foundations built on this soil become waterlogged. 

Soil Properties 

Clay soil is very sticky, highly compressible, and has low strength. Its other properties include: 

Fine Particles 

Clay has the smallest particle size of any soil type. Its particles are so small that they are invisible to the naked eye. 


Clay soil’s fine particles make its structure dense. The particles usually bond tightly together, leaving no gaps like soils with larger particles. This density is what makes clay soil heavier and thicker than other soil types. 

Less Permeable 

Clay may be porous but it’s the least permeable soil. Its low permeability means water will take a long time to percolate through, resulting in poor drainage and low infiltration rates. 


Clay soil expands when it encounters water and shrinks when it dries up. The expansion can cause an upheaval when it gets wet, while the shrinkage can cause gaps to form under your foundation. This shrink-swell cycle can lead to foundation settlement and cracks. 

Should I Build My Foundation on Top of Clay Soil? 

Clay soil has some undesirable properties such as being compressible, poor drainage, and low strength that can cause problems. 

  • As the soil expands, it puts pressure against your home’s foundation walls, potentially causing them to bow or crack. Cracks make your walls vulnerable to water seepage. 
  • As the soil contracts, it creates fissures between the foundation wall and the backfill, allowing water to run down and settle along the base of your foundation walls. 
  • Also, water that seeps through the soil can find its way into your slab, making your basement susceptible to damage from water, moisture, and mold. 

How to Improve Clay Soils 

The good news is that there are several measures you can take to improve the soils around and under your foundation. The following techniques work well to curb the shrink-swell cycle of clay soil responsible for foundation damage. 

Chemical Stabilization 

Adding stabilizers such as lime, fly ash, and cement to clay can help alter this soil’s shrink-swell properties. 

Clay Soil Replacement 

If the onsite soil has a high clay content – or is made of clay entirely – and is located at shallow depths, consider excavating a part of the soil and replacing it with compact structural fill material that doesn’t shrink or swell. 

Moisture Maintenance 

Clay soil’s moisture content changes with the seasons. If you can find a way to maintain a balance in the moisture content, you can alleviate the expansive characteristics of clay soil. Some ways to maintain moisture in the soil are installing foundation landscaping or watering the dirt using a soaker hose (porous tube) that weeps along its length. 

Foundation Support 

Some deep foundation solutions like push piers can transfer structural load through unstable or expansive clay soils to deeper and solid bedrock. 

Is Your Foundation Settling? 

A stable and secure foundation is vital to a successful construction project. Failure to account for the expansive features of clay soil can lead to catastrophic damages and expensive repairs. 

At Complete Basement Systems, we take the time to identify your settling foundation’s root cause and then recommend a lasting solution. Contact us today to schedule a free foundation inspection

Serving Greater Denver area, Colorado Springs, Eastern Colorado, and parts of Nebraska and Wyoming

Colorado Springs, CO

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Palmer Lake, CO 80133

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4686 Ivy St
Denver, CO 80216