You found a beautiful property on the Front Range. The house is stunning, the barn is perfect, and the views are incredible.
But what is hiding underneath the grass?
All major population centers in Colorado are partially located on expansive soils. In fact, these soils cause more financial loss nationwide than floods, hurricanes, tornadoes, and earthquakes combined. If you buy a home built on untreated bentonite clay without the proper foundation engineering, you could be facing a catastrophic repair bill.
Here is what you need to know about Colorado’s shifting ground and how to protect your investment.
Does the Soil Contain “Bentonite” (Expansive Clay) That Ruins Foundations?
Quick Summary: The Dirt That Breathes
- The swell and shrink cycle: Bentonite is a highly absorbent clay found throughout Colorado that expands dramatically when wet and shrinks when dry. This constant movement can destroy a home from the ground up.
- Massive pressure: Expanding clay can exert up to 30,000 pounds of force per square foot. This pressure can bow basement walls, snap slabs, and lift structures.
- Engineering is required: You cannot pour a standard slab directly on highly expansive soil. Homes in these zones need specialized foundations like deep drilled piers.
- Water is the enemy: The best defense is aggressive moisture control. Bad drainage, pooling water, and planting too close to the house trigger swelling.
You don’t have to fear bentonite. You have to respect it—and verify the engineering and drainage plan that keeps it from moving.
1. What Exactly Is Bentonite Clay?
Colorado soil is naturally dry and consists of varying mixtures of sand, silt, and clay. The danger lies in a specific clay called bentonite.
Bentonite is rich in montmorillonite, a mineral formed from weathered volcanic ash. Its fine particles absorb water like a sponge.
- During snowmelt or heavy rain, the clay expands in volume by 10% or more.
- During drought, it dries out and shrinks, leaving voids and fissures.
- This heave-and-drop cycle is what tears structures apart over time.
2. The Symptoms of Soil Damage
Expansive soil movement is rarely uniform. One side of the house can be wet (leaky gutter) while another stays dry—creating “differential heaving.”
Visual clues of foundation failure
- Sticking doors and windows: Frames fall out of square.
- Stair-step cracks: Jagged cracking in brick siding or cinderblock basement walls.
- Bowing walls: Basement walls can lean inward due to pressure.
- Heaving slabs: Garage floors, basement slabs, and driveways crack and lift unevenly.
Ask for the seller’s property disclosures and any prior foundation repair documentation before you waive inspections.
3. How Builders Defeat Bentonite
Because expansive soils are common along the Front Range and Eastern Plains, builders have engineered ways to build safely.
Common mitigation strategies
- Pier and beam foundations: Concrete piers are drilled down to stable layers, bypassing active clay. The home is supported on beams above the moving soil.
- Over-excavation: Expansive clay is removed to around 10 feet below the foundation. Stable fill is brought in, compacted, and built on.
- Chemical treatment: In some cases, chemicals are injected to reduce swelling potential.
The original soils (geotechnical) report. It is the blueprint for how the home was engineered to survive the clay.
4. Protecting Your Home as a Buyer
Your first line of defense is disclosure. Colorado sellers must disclose known material defects, including expansive soils and mitigation steps taken.
What to request
- Soils report (if available)
- Foundation engineering plans or pier specifications
- Any prior repair invoices or structural engineer letters
Moisture management is the ongoing job
- Keep water directed away from the foundation.
- Do not allow sprinklers to spray within five feet of the house.
- Plant large trees at least fifteen feet away to avoid moisture disruption and root impact.
Let Us Verify Your Foundation Security Together
Managing a rural property is complex enough without worrying if your house is slowly shifting. When we work together, we take the guesswork out.
We help you review disclosures, look for signs of foundation stress, and connect you with trusted structural inspectors so you can move forward with confidence.
Contact Us Today to simplify your home search before you buy.
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Frequently Asked Questions (FAQ) About Bentonite Clay
Can I fix a foundation that is already damaged by bentonite?
Yes, but it is expensive. Foundation repair companies can install helical piers deep into bedrock to lift and stabilize the home permanently. This often costs tens of thousands of dollars.
Does bentonite affect horse barns and arenas?
Absolutely. Even without a basement, concrete barn aisles and tack room slabs poured over untreated bentonite can crack and heave. Heavy structures need proper excavation, grading, and engineered bases.
Is bentonite clay only found in the mountains?
No. The Front Range and Eastern Plains contain highly expansive soils. Counties like Logan, Morgan, and Washington have soils with very high swelling potential.