Foundation Types
Slab Foundation Repair
The short answer
Slab foundation repair stabilizes a concrete slab-on-grade that has settled or heaved, usually by installing piers (pressed concrete or steel) beneath the perimeter to lift and support it. Most Austin homes built since the 1980s are slab-on-grade, and typical repairs run $4,000–$12,000 depending on the number of piers.
Why slabs struggle on Austin clay
A slab-on-grade foundation is exactly what it sounds like: the house is poured on a single reinforced concrete slab sitting directly on the soil. It’s the standard for Austin homes built since roughly the mid-1980s — efficient to build, but with one vulnerability here: it has no buffer between the structure and our expansive clay. When the clay swells and shrinks with the seasons, the slab rides every bit of that movement.
That’s why slab problems in Central Texas usually show up as differential movement — one corner or edge drops (settlement) or the center pushes up (heave) — producing diagonal cracks at door frames, separating brick, and sloping floors.
How slab repair works
The standard repair is underpinning:
- The contractor digs access points around the slab’s perimeter.
- Piers are installed down to stable soil or load-bearing strata — pressed-concrete pilings for most jobs, steel push piers for deeper instability, or helical piers where soil is tricky.
- Hydraulic jacks lift the settled areas back toward level.
- The piers permanently support the foundation at the corrected elevation.
Where the slab’s interior has dropped, crews can pier through the slab or use polyurethane foam or mudjacking to raise it.
How to tell if your slab is settling or heaving
Look for diagonal cracks radiating from the corners of doors and windows, a section of exterior brick veneer stair-stepping upward, a gap opening between baseboard and floor in one room but not others, interior doors that stick or won’t latch, and tile or hardwood cracking in a straight line across a room. One or two of these on their own can be normal; several together, especially if they’re worsening, point to real movement.
Not every crack is foundation-related, though. Slabs get hairline, straight cracks along their control joints (the saw-cut lines poured in to control where the concrete shrinks as it cures) — that’s expected and not a structural issue. The pattern worth acting on is diagonal, widening, or tied to door and window frames going out of square, especially paired with sloping floors. See the full symptom checklist if you’re not sure which you’re looking at, or the foundation crack types guide for how wall and brick cracks fit the same pattern.
Post-tensioned vs. conventional slabs — why it matters for repair
Many Austin slabs built since the 1990s, especially larger or newer homes, are post-tensioned (PT) rather than conventionally reinforced with plain rebar. A PT slab has steel cables (tendons) run through it and stressed after the concrete cures, putting the whole slab under compression — which resists the cracking and bending expansive clay tends to cause far better than a plain rebar slab does.
The repair-relevant catch: those tendons stay live under tension inside the slab for its life. Before any drilling, coring, or interior piering, a competent crew locates them first (with ground-penetrating radar or a tendon locator) and works around them — cutting a live tendon is a real safety and structural risk, which is exactly why the Post-Tensioning Institute publishes field guidance for modifying PT structures. If you’re not sure whether your slab is post-tensioned, your original building plans (or an inspector) will tell you; it changes how piers or access points get placed, not whether repair is needed.
What it costs and what protects the repair
Budget $4,000–$12,000 for a typical Austin slab repair; see the full cost guide for the breakdown. Whatever you spend on piers, protect it by controlling water — grading, gutters, and steady summer foundation watering keep the clay’s moisture stable so new low spots don’t develop. Compare your options in pier & beam vs. slab.
Frequently asked questions
How do you repair a slab foundation?
By underpinning it: a contractor installs piers (pressed concrete or steel) at intervals beneath the slab's perimeter, then uses them to lift the settled areas back toward level and hold them there. Interior piering through the slab is used when the center has dropped.
How much does slab foundation repair cost in Austin?
Most slab repairs run $4,000–$12,000. The driver is pier count — 8 to 20 piers is typical — at roughly $300–$800 per pressed-concrete pier or $1,200–$2,500 per steel pier.
Can a slab foundation be fixed permanently?
Piering can permanently stabilize the settled areas, and reputable companies back it with a transferable warranty. But because the surrounding clay keeps moving, controlling water with drainage and consistent foundation watering is essential to prevent new problem areas.
What causes slab foundations to fail in Texas?
Expansive clay. It swells when wet and shrinks in drought, repeatedly lifting and dropping the slab. Add poor drainage, large trees pulling moisture from the soil, or plumbing leaks, and movement accelerates.
Is my slab foundation post-tensioned?
Homes built in Austin from the 1990s onward, especially larger or newer construction, are more likely to be post-tensioned — check your original building plans or ask an inspector. It doesn't change whether repair is needed, but it changes how piers or plumbing access get installed, since the internal steel tendons must be located and avoided first.
Does a crack in my slab always mean foundation failure?
No. Hairline, straight cracks along a slab's control joints (the saw-cut lines) are normal shrinkage as concrete cures and aren't a foundation problem. Diagonal cracks that widen, track with door or window frame separation, or show up alongside sloping floors are the pattern worth having an engineer look at.