Caliche, Sulfates and Settling: Why Concrete Cracks on Las Vegas Soil

Quick answer

Las Vegas Valley concrete usually cracks or sinks because water reaches soil under the slab, whether from irrigation, leaks or runoff, and some local soils settle or swell when wetted. Sulfate-bearing soils can also wear down concrete made with ordinary cement. Fix the water source first, then decide whether to seal, lift, resurface or replace.

Last updated October 22, 2026

Concrete cracks everywhere, because it shrinks as it dries. Control joints exist to give those cracks a straight place to form. But when a Las Vegas driveway sinks at one corner, a patio pulls away from the house, or the edge of an old walk turns soft and crumbly, the cause is usually something in the ground. This guide explains the soil and water conditions behind most local concrete problems and how to decide on a fix.

The ground under the valley

The Las Vegas Valley is a desert basin filled with sediments washed down from the surrounding mountains. Soils change a lot over short distances, from coarse gravel near the mountain fronts to finer silts and clays in lower areas. A few local features matter most for concrete.

Caliche

Caliche is soil cemented together by lime. University of Nevada Extension describes it as a layer that can be a few inches or several feet thick and that acts like a hardpan, blocking drainage. For concrete, caliche is hard to dig, which affects excavation cost, and it can cause water to perch above it rather than draining away. Water that sits on top of caliche under a slab can soften the soil above it.

Collapsible soils

Some desert soils are loose and dry, held together by weak bonds that hold up fine until they are soaked. When water reaches them for the first time, they can compact and drop. The Nevada Bureau of Mines and Geology has mapped collapsible soil potential in the valley as part of its subsidence studies. On a home lot, the trigger is usually irrigation, a leak or ponded runoff next to a slab.

Expansive soils

Finer clay-rich soils in parts of the valley can swell when wet and shrink when dry. Research on the valley has found expansion potential tends to be higher in flatter areas with finer, more plastic soils. Seasonal wetting from monsoon storms or watering cycles can push slabs up or let them drop.

Sulfates

Some Southern Nevada soils contain sulfate salts. Over time, sulfates in soil moisture can react with ordinary cement and break down concrete, often showing up as a soft, flaking or crumbling zone near the ground line. This is why sulfate-resistant Type V cement is widely used locally, and why Boulder City's driveway apron standards specify a Type V mix.

Earth fissures and subsidence

Decades of groundwater pumping caused parts of the valley floor to subside, and the Nevada Bureau of Mines and Geology has mapped earth fissures and subsidence-related faults. These affect a small share of properties, but if cracks line up across your slabs, block walls and the street, mention it to the contractor and consider a geotechnical engineer.

Water is usually the trigger

Desert soil under a slab is often stable as long as it stays dry. Most problems start when water is added:

Drip emitters and sprinklers next to driveways, walks and patios
Leaking irrigation lines or valves under or beside slabs
Pool leaks and splash-out around pool decks
Downspouts and roof runoff dumping at slab edges
Monsoon runoff collecting in a low corner or against a block wall

Turf conversions can help, since desert landscaping usually uses less water, but drip lines placed right against a slab still cause trouble. Keep emitters back from concrete edges.

Reading the cracks

Hairline cracks along or between joints: usually normal shrinkage.
Many fine surface cracks soon after the pour: often fast drying during a hot or windy pour. See pouring concrete in Las Vegas heat.
One side lower than the other: settlement, often from water under that section.
A slab tilting toward a planter or the yard: irrigation softening or collapsing soil at that edge.
Soft, flaking concrete near the ground: possible sulfate attack or repeated wetting and drying with mineral-rich water.
Cracks running in a line across several slabs and walls: worth a professional look.

When repair makes sense

Repair is often the practical choice when cracks are narrow, slab sections are still level or sank as one piece, the surface is sound, and the water source can be fixed. Options include crack and joint sealing, slurry or foam lifting, patching and resurfacing. See concrete repair and leveling.

When replacement is the better call

Cracking and settling across most of the slab
Panels tilted in different directions
Widespread crumbling or soft concrete
The slab drains toward the house or holds water
Repeated repairs that keep failing

Replacement lets you fix the cause: remove wet or loose soil, compact the subgrade, add a proper base, move irrigation, correct the grade and use a cement suited to the soil.

When to call an engineer instead

If you see growing cracks in stucco or the foundation, doors and windows that start sticking, or gaps opening between the house and its slabs, the problem may involve the house itself. A Nevada-licensed structural or geotechnical engineer can evaluate it before any concrete work.

Questions to ask a contractor

What do you think caused this, and how will your fix address the water?
Is this slab a good candidate for lifting?
If we replace it, what base, cement type and joint spacing will you use?
Will you move irrigation away from the new slab?
Can you share your Nevada State Contractors Board license number and insurance certificate?

When you're ready, request a concrete contractor and include photos of the cracks with a coin or tape measure for scale.

Frequently asked questions

Is caliche bad for concrete?

Caliche itself is hard and can support a slab, but it's difficult to dig and can block drainage so water collects above it. The bigger concern is usually what happens to the softer soil around it when it gets wet.

Will switching to desert landscaping stop my slabs from sinking?

It can help by reducing water, but drip emitters placed against concrete edges still wet the soil. Keep irrigation back from slabs and fix any leaks.

What is Type V cement?

It's a sulfate-resistant portland cement. It's commonly used in Southern Nevada because some local soils contain sulfates that can damage ordinary concrete over time. Ask your contractor what they plan to use.

Sources and further reading

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