Around Denver, slabs can heave up from swelling clay or sink from settling backfill and washouts. Sunken slabs can often be lifted with cement slurry or foam; heaved panels are usually ground or replaced. Crack sealing, patching and resurfacing handle surface damage. Fix downspouts and sprinklers first, and have an engineer look at foundation cracks.
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Not every cracked or uneven slab around a Denver home needs to be torn out. Depending on the cause, concrete can often be lifted, sealed, patched or resurfaced for less money and disruption than replacement. The catch on the Front Range is that slabs move up as well as down, and the right fix depends on which way yours went and why.
Why concrete moves and cracks around Denver
- Swelling clay. The Colorado Geological Survey describes expansive clay as the state's most significant geologic hazard and lists cracked and heaved sidewalks, patios, driveways and garage floors as common signs. When the clay under a slab gets wet, it can push panels up; when it dries, they can drop.
- Heaving bedrock. In parts of the Front Range piedmont near the foothills, including areas of Jefferson and Douglas counties, steeply tilted layers of expansive claystone bedrock can heave unevenly. The CGS and Jefferson County have mapped areas where this is a concern.
- Settling backfill. Soil placed around foundations and along driveway edges during construction can compress and sink, especially when roof runoff soaks it.
- Water. Downspouts, leaking sprinkler lines and heads that spray onto slabs wet the soil and can wash out voids.
- Freeze-thaw and deicers. Repeated freezing and thawing, plus deicing chemicals, cause surface scaling and spalling, especially on concrete that wasn't air-entrained or was finished poorly.
- Shrinkage. Some cracking is normal as concrete dries, particularly where joints are too far apart.
Repair options
- Slab lifting with cement slurry (mudjacking): a cement-based grout is pumped through drilled holes to raise a sunken slab and fill voids.
- Polyurethane foam lifting: an expanding foam is injected through smaller holes; it is light and cures quickly.
- Grinding: a raised edge at a joint can be ground down to remove a trip lip.
- Crack and joint sealing: flexible sealants keep water and salt out, which slows further damage.
- Patching and resurfacing: repair mortars and thin overlays can renew scaled or spalled surfaces on slabs that are otherwise sound and stable.
- Section replacement: badly broken or heaved panels are cut out at joints and repoured.
Heaved versus sunken
Lifting only works on slabs that have dropped. A panel that has been pushed up by swelling soil usually can't be pushed back down; the options are grinding a small lip, or removing and replacing the panel after dealing with the water that caused the swell. Lifting a neighboring panel to match a heaved one is sometimes possible but can just move the problem. That is why it pays to have a contractor explain what they think caused the movement before you choose a fix.
Fix the water first
CSU Extension advises grading soil so water drains away from the house, keeping sprinkler spray at least several feet from the foundation, and leaving downspout extensions in place. The same steps protect walks, patios and driveways. Many repairs fail because a downspout or sprinkler keeps soaking the same spot. Denver Water and other utilities also require prompt repair of leaking irrigation systems during the watering season, which helps your concrete too.
When it might be structural
Cracks in a driveway or patio are usually not structural. Cracks in foundation walls, a basement floor that is heaving, stair-step cracks in brick, or doors and windows that suddenly stick can signal foundation movement. In those cases an evaluation by a structural or geotechnical engineer is the right first step.
Questions to ask
- Has this slab heaved or settled, and what do you think caused it?
- Will you lift, grind, patch or replace, and why?
- What will the drill holes or patches look like afterward?
- Is there a warranty if a lifted slab settles again?
Not sure which way to go? Read how swelling soil affects concrete in Denver, then mark your request as urgent if there's a trip hazard and request a repair contractor.
See how it works
Frequently asked questions
Can a heaved slab be lowered?
Generally not. Slab lifting raises concrete that has dropped. Heaved panels are usually ground down if the lip is small, or removed and replaced after the water that caused the swelling is controlled.
Is mudjacking or foam lifting better?
Both can raise sunken slabs. Cement slurry lifting is a long-established method; polyurethane foam uses smaller holes, is lighter and cures quickly. The right choice depends on the slab, the voids beneath and the contractor's experience.
Are cracks in my driveway a foundation problem?
Usually not. Flatwork cracks are common on Front Range soils. Cracks in foundation walls, a heaving basement floor or sticking doors and windows can point to foundation movement and are worth a structural or geotechnical engineer's evaluation.
Sources and further reading
- Colorado Geological Survey: expansive soil
- Colorado Geological Survey: heaving bedrock hazards, Douglas County (SP-42)
- CSU Extension PlantTalk: expansive soils
- Jefferson County: geology and dipping bedrock
- City and County of Denver: right-of-way contractor licenses
- Denver DOTI: sidewalk repair and construction
- City of Aurora municipal code: work in the public right-of-way
- City of Lakewood: contractor registration
- City of Arvada: right-of-way permits
- Town of Castle Rock: right-of-way permit information
- Highlands Ranch Community Association: covenants and improvements
- Denver Water: summer watering rules
- Colorado 811: homeowners
- American Concrete Institute (ACI)
- Portland Cement Association (PCA)