Slab Foundation Repair San Antonio, TX.

Where your house sits relative to the Balcones Escarpment tells us most of what we need to know before we ever pull up. On the east and southeast side of town, out along the Loop 410 corridor toward the Eastside, slabs sit on deep Houston Black clay with a plasticity index that routinely runs 40 to 60. That soil swells every time it rains and shrinks hard through an August drought, and a slab-on-grade never really stops riding those swings, it lifts in wet months and drops in dry ones until the movement piles up at corners and door openings as diagonal cracking.

Push west and north toward Helotes, Leon Valley, and Hill Country Village and the problem flips. There's less expansive clay, but the soil is thin over karst Edwards limestone and the rock surface underneath is anything but flat. Slabs there settle where old fill was never compacted or where soil has washed down into solution cavities. Same cracked drywall, completely different cause, which is why we diagnose your specific address rather than hand you a one-size template.

How a slab repair goes on a San Antonio home

Why depth is the whole game on Bexar County clay

In the high-plasticity clay zones across the metro, the active zone, the band of soil that actually changes volume with moisture, commonly reaches 10 to 15 feet below grade. Anything anchored inside that band moves with it. That's the core reason we use galvanized steel piers driven in connected sections: they reach past the moving soil to load-bearing strata. Pressed-concrete piers are stacked cylinders that often stop short inside that same active clay and can drift over time.

The elevation survey does more than find the low spots. It separates a slab that has dropped fairly uniformly, often tolerable and not structurally urgent, from one with a steep differential gradient that's putting the concrete into bending and tearing structural elements. Two homes on the same street can show identical wall cracks and need very different plans, and the contour map is what tells them apart.

None of it lasts, though, if water keeps cycling under the slab. Drainage is a repair prerequisite here, not an afterthought. You can read more about how we handle surface water on our drainage page and how we stop soil loss on the erosion control side.

What shapes the plan for your slab

Every San Antonio project is scoped from measured data, but a handful of site factors carry the most weight:

• Active-zone depth, in local clay it runs 10 to 15 feet, so piers have to penetrate well below it to reach soil or rock that ignores the seasons.
• Differential vs. uniform settlement, a steep tilt across the slab is urgent; an even drop often isn't, and the survey tells us which you have.
• Drainage grade, you want roughly 6 inches of fall over the first 10 feet away from the foundation to dampen moisture swings under the concrete.
• Drought watering, a soaker line held 12 to 18 inches off the stem wall in dry stretches keeps the clay near equilibrium and limits shrinkage settlement.
• Pier spacing and load, placement follows the tributary load each pier carries, so it clusters under bearing walls and opens up under interior panels.
• Where you sit on the escarpment, deep clay east and southeast, thin soil over irregular limestone north and west, each calling for a different target depth.

San Antonio slab repair questions, answered