A slab-on-grade home sits on a concrete slab poured directly on the ground, with no crawl space underneath. When the soil under or beside that slab changes, the slab can crack, tilt or sink. In Las Cruces, those changes often come from water.
This page covers the signs of slab movement, the causes behind it, and how repair is matched to the cause. If you want to talk it through, (575) 249-7768 connects you with licensed and insured local foundation repair professionals.
Signs a slab may be moving
Slab problems often show up inside the house first. Because the floor sits on the concrete, movement can appear in the finishes before you see anything outside.
- Cracked floor tile, especially cracks that line up across several tiles
- Gaps between the baseboards and the floor, or between walls and the ceiling
- Floors that slope or feel uneven when you walk across a room
- Doors and windows that stick or no longer latch
- Diagonal cracks in drywall running from the corners of doors and windows
- Cracks in the slab itself, or in stucco on the outside walls
- Sunken driveways or patios next to the house
Not every crack means trouble. Thin hairline cracks from concrete shrinkage are common. Cracks that widen, have one side higher than the other, or run in a stair-step pattern deserve a closer look.
A simple habit helps. Photograph the crack with a ruler or coin beside it for scale, write the date on the photo, and compare every few weeks.
What can move the soil under a slab
A slab is only as steady as the ground beneath it. Changes in soil moisture are a common cause of foundation movement, and the Las Cruces climate swings between dry and wet.
Precipitation is very light from October to June. Early summer brings long hot stretches, sometimes over 100 degrees F. Then the late-summer monsoon arrives with heavy afternoon thunderstorms. Soil around a foundation can go from dry to soaked in a short time.
Local soil adds another factor. Caliche, a cemented whitish layer common in southern New Mexico, keeps water from moving deeper into the ground. In the Cruces soil series near town, that layer sits about 8 to 20 inches below the surface on broad basin floors. Where it is present, roof and yard runoff can collect near the house instead of draining away.
Grading matters too. Heavy storms and nearby arroyos can send water toward a home when the ground slopes the wrong way. This applies to older streets in the Mesilla Valley and to newer subdivisions spreading toward the Organ and Robledo Mountains.
Other sources of water near the slab include:
- Gutters and downspouts that empty right beside the house
- Irrigation running close to the walls
- Plumbing leaks, including leaks in lines under the slab
How repair is chosen
There is no single fix for a slab. The right repair depends on what is causing the movement, the type of foundation, and how much of the house is affected.
Some examples of options a contractor may discuss:
- Piers to support or stabilize the foundation
- Lifting sunken concrete, such as a patio or walkway slab
- Sealing cracks
- Correcting drainage, such as regrading or redirecting downspouts
The cause comes first. A slab that moved because water pooled along one wall needs a different plan than one affected by a leak below the floor. Sealing a crack or lifting a slab without fixing the water problem may not hold up.
What an inspection looks at
A good inspection looks at cracks, floor levels, doors and windows, and the drainage and grading around the house. The goal is to find the likely cause before any repair is recommended.
For significant movement, or during a home sale, you may want an evaluation from a licensed structural engineer in addition to a contractor's inspection. Contractors give a quote after seeing the problem, so cost depends on what they find.
Before you hire
In New Mexico, the Construction Industries Division (CID) licenses building contractors. GB-2 is the residential building classification, and GB-98 is the general building classification. You can look up a contractor's license with CID before you hire.
A few other steps are worth taking:
- Ask for a written scope of work that describes what will be done.
- Ask whether the job needs a building permit from the City of Las Cruces or Doña Ana County. The contractor can explain what applies.
- Check your homeowner insurance policy. Many policies exclude damage from earth movement or settling.
Help across the Las Cruces area
Callers in Las Cruces can be connected with local contractors for slab concerns, from East Mesa and Sonoma Ranch to Mesilla Park and University Park. Help is also available in Mesilla, Doña Ana, Organ and Anthony, and across Doña Ana County.
If you have noticed cracked tile, sticking doors or a floor that no longer feels level, call (575) 249-7768. You will be connected with licensed and insured local professionals who can inspect the slab and explain the options.