What slab foundation repair involves
A slab-on-grade foundation is a single reinforced concrete pour sitting directly on prepared soil, usually with thickened beams running beneath the load-bearing walls. There is no crawl space and no accessible void underneath. When the soil beneath part of that slab loses support, the slab follows it down.
Repair works by bypassing the problem soil entirely. Piers are installed beneath the slab's perimeter beam or at interior points, driven or drilled down until they reach strata capable of carrying load without seasonal movement. The weight of the structure is then transferred onto those piers, and where appropriate the slab is lifted back toward its original position before being locked off.
The critical word is bypassing. Nothing about the repair changes the clay. It remains as expansive as it ever was, which is why drainage correction and moisture management belong in the same conversation as the piers.
Why Texas slabs move
The underlying mechanism is covered in detail in our guide to why Texas soil moves foundations, but the slab-specific version is this: a slab is a large, relatively rigid plate resting on a surface that changes shape. It cannot flex much. When the soil under one edge shrinks away during a drought and the soil under the opposite edge stays moist, the plate is asked to span the gap, and concrete in tension cracks.
Three patterns dominate in Texas:
- Edge drop. The perimeter settles as soil beneath the beam dries and shrinks, most often on the elevation with the most sun exposure or the least irrigation.
- Centre heave. The middle of the slab rises because moisture accumulates there — commonly from a leaking line, sometimes simply because the covered centre never dries while the exposed perimeter does. Counter-intuitively this is often the more damaging pattern.
- Localised settlement. A discrete area drops, usually traceable to a specific cause such as poorly compacted fill, a leaking drain, or a tree drawing moisture out.
Signs that point specifically at a slab
Many foundation symptoms are common to any construction type. A few point at slab behaviour in particular: cracks in the slab itself visible in a garage or beneath lifted flooring; tile or laminate tenting along a line across the floor; a visible gap opening between the slab edge and the brick course above it; and doors on a single elevation that all bind in the same direction.
Hairline cracking in a slab is not automatically movement. Concrete shrinks as it cures and fine cracks in the first year or two are common. What matters is width, change over time, and whether the pattern lines up with the damage above. Reading cracks correctly is a page of its own.
Underpinning methods used in Texas
| System | How it works | Suits |
|---|---|---|
| Pressed concrete pilings | Cylindrical concrete segments hydraulically pressed into the soil using the house as reaction mass | The common Texas residential choice; well suited to deep clay profiles |
| Steel pilings | Steel pipe sections driven to refusal, reaching deeper and through harder layers than concrete segments | Deeper bearing strata, heavier loads, variable fill |
| Helical piers | Screw anchors turned into the ground to a measured torque, which correlates with capacity | Lighter structures, limited access, situations where installed capacity must be verified |
| Drilled piers / bell-bottom | A shaft drilled and filled with reinforced concrete, sometimes belled at the base | New construction and engineered repairs; slower and more disruptive to install |
| Polyurethane foam injection | Expanding structural foam injected beneath the slab to fill voids and raise it | Void filling and lifting lighter slabs; not a substitute for underpinning a settled house |
There is no universally correct system, and a contractor who installs only one will naturally recommend it. What matters more than the brand is the depth — piers must reach soil that does not move seasonally. LevelUp CS reports 12 to 15 feet as typical in their part of the DFW area. A pier that stops in the active zone will move with it.
Perimeter, interior and tunnelling
Perimeter piers are installed from outside, excavating beside the beam. This is the least disruptive and least expensive approach, and it is sufficient when the movement is at the edge.
Interior support is harder, because the point needing support sits under the middle of the house. There are two routes. The slab can be broken through from inside, which means removing flooring and working in the room. Or a tunnel can be dug from outside beneath the slab to reach the point, which costs considerably more but leaves the interior untouched. For an occupied house with finished floors, tunnelling is often worth the difference.
What happens during the lift
Once piers are installed, hydraulic jacks transfer load onto them and raise the slab. The lift is done gradually and in coordination across multiple points, because concrete that has cracked along a line will move as separate pieces, and lifting one faster than its neighbour opens the crack further.
An important expectation to set: a house is rarely returned to dead level, and should not be. The goal is to recover elevation and close the structure back up, stopping at the point where further lifting would cause more damage than it corrects. Plaster, tile, plumbing and masonry have all settled into the current shape over years. Our house leveling page covers how much recovery is realistic and why chasing a perfectly flat floor is usually the wrong target.
The plumbing risk nobody budgets for
Under-slab lines move when the house moves
Supply and drain lines run beneath the slab. Lines already strained by years of settlement can fail during a lift. Thomas Engineering, a Texas professional engineering firm, notes that under-slab plumbing repairs can equal or exceed the cost of the foundation work itself. Ask about a hydrostatic test before and after the work — it will not prevent a failure, but it establishes what condition the lines were in beforehand.
The relationship runs both ways. A leaking line is itself a common cause of localised settlement, by saturating and softening soil in one area. Ruling a leak out before underpinning is worth doing, because a leak left in place will keep working on the soil around the new piers.
What drives the cost of slab repair
The number of piers is the largest single factor, followed by depth and access. Published third-party estimates give a sense of scale: Thomas Engineering estimates $8,000 to $25,000 for slab repairs on an average home under 2,500 square feet, while LevelUp CS quotes $4,000 to $12,000 for slab repair in their DFW service area, with smaller jobs around $2,500. G.L. Hunt puts pier installation at roughly $1,000 to $3,000 per pier.
Those figures are published by other companies and are included here for orientation only. They are not our prices, and we do not quote. The relevant number comes from a contractor who has measured your house.
What should make you cautious is a quote well below the others. The usual explanations are fewer piers than the job needs, piers that stop short of load-bearing strata, or a warranty that does not transfer on sale — all invisible on completion day and expensive later.