Slab Foundation Repair San Marcos, TX.
A San Marcos slab can sit on fractured limestone at one corner and swelling Blackland clay at the other. We measure the difference to 1/64 inch, then stabilize on galvanized steel piers driven past the moving soil.
How a San Marcos slab repair actually unfolds
Free elevation survey to ±0.01 in.
We shoot a grid of points under the roofline to map the true shape of the slab, exactly which zones dropped and which heaved.
Engineer-backed diagnosis
You get a written plan that separates settlement from heave, because lifting an already-heaved corner only makes the distortion worse.
Galvanized steel piers to load-bearing strata
Piers are driven hydraulically through the active clay until drive resistance confirms they've reached competent rock or dense soil below seasonal moisture.
Lift, secure, and manage the water
We correct the slab to a controlled position and address the drainage or grading feeding the movement, so the fix holds instead of resetting.
Why the Balcones Fault makes San Marcos slabs move
San Marcos straddles the Balcones Escarpment, the seam where the hard Edwards Plateau limestone to the west meets the high-plasticity Blackland clay that runs the corridor east of Interstate 35. The change is abrupt, the fault system throws soil and rock discontinuities into the same neighborhood, occasionally into the same lot. One corner of a slab can bear on near-surface caliche while the opposite corner floats on clay that swells several inches with the seasons.
East of I-35 in Hays County, that clay is genuinely aggressive: plasticity indices routinely clear 40 and often reach 60 or higher. The active zone, the depth where seasonal moisture keeps changing soil volume, runs 8 to 15 feet down here, deeper where the clay is thick and drainage is poor. A slab poured straight onto it is essentially riding a cushion that shrinks in drought and heaves after a wet spring.
That's why we treat this as a soil-moisture problem first and a structural one second. The differential between a dry Central Texas summer and a soaked spring is enough to crack interior finishes, bind doors, and eventually fracture the slab. Correcting the foundation without reading where it sits in that geologic picture just buys time until the next cycle.
Settlement and heave are not the same repair
The elevation data tells us whether a low reading is a zone that settled or a neighboring zone that heaved upward. It's a critical distinction: lifting a heaved area with piers deepens the distortion instead of curing it.
That's the whole point of surveying before we quote, the diagnosis drives which locations get piers and how much lift each one applies.
Signs your San Marcos slab is chasing the moisture
A few patterns show up again and again on homes over the Blackland clay:
- Stair-step cracks following the mortar joints in brick veneer, the classic marker of differential movement
- Doors and windows that stick in wet months, then swing freely once the ground dries
- Interior sheetrock cracks radiating from the corners of door frames
- A finished grade that falls less than 6 inches over the first 10 feet, letting water pool at the grade beam
- Gaps opening between the slab and the brick, or between countertops and the wall
- Horizontal cracking in the brick units or slab soffit, a sign of more serious structural distress worth a survey soon
San Marcos slab repair questions
What's a realistic price range for a San Marcos slab repair?
My house is east of I-35, does that change anything?
Do you fix what's causing the movement or just lift the slab?
How is the free elevation survey different from a guess?
Can we stay in the house while you work?
How do I keep this from happening again?
Is the warranty something the next owner gets too?
Book your free
foundation inspection.
Tell us where you are and what you’re seeing. A GroundLock structural advisor confirms within one business hour.
All foundation services in San Marcos
Every GroundLock service, available throughout San Marcos and the surrounding area:
Get your free foundation inspection.
A licensed inspector measures your slab elevation to ±0.01 in. (1/64 in.) and gives you a written, engineer-backed plan with zero pressure.