Foundation repair terms, defined
The words a Texas contractor or engineer will use, in plain language. Knowing them is the difference between following a quote and nodding along to one.
- Expansive clay
- Soil that physically changes volume as its moisture content changes. It swells when wet and shrinks when dry. This is the cause of nearly all foundation movement in Texas.
- Houston Black
- The Texas state soil and the dominant clay of the Blackland Prairie. A Vertisol, documented by USDA-NRCS at a plasticity index of 40–60.
- Plasticity index
- The engineering measure of how much a soil shrinks and swells. Building codes classify soil as expansive at 15. Blackland Prairie clay runs two to four times that.
- Slab-on-grade
- A single reinforced concrete pour sitting directly on prepared soil, with no crawl space beneath. The foundation under most Texas homes built since the 1960s. See slab foundation repair.
- Pier and beam
- Framing carried on spaced supports above a ventilated crawl space. Common in Texas homes built before the 1960s. See pier and beam repair.
- Differential settlement
- One part of a structure dropping relative to another. The difference is what cracks brick and racks door frames, not the absolute amount of movement.
- Heave
- The opposite of settlement: soil swelling and pushing a foundation upward. Centre heave, where the middle of a slab rises, is often more damaging than edge settlement.
- Underpinning
- Installing piers beneath an existing foundation to transfer its weight onto soil that does not move seasonally. The core of most slab repairs.
- Bearing strata
- The depth at which soil or rock will carry load without seasonal movement. A pier that stops short of it moves with the clay — which is how a cheap repair fails.
- Pressed piling, steel piling, helical pier
- The three underpinning systems in common Texas residential use. Pressed concrete segments are driven using the house as reaction mass; steel pilings reach deeper through harder layers; helical piers screw in to a measured torque that correlates with capacity.
- Slab jacking
- Raising a slab by injecting material beneath it — usually polyurethane foam. Suits settled garage slabs, walkways and patios; not a substitute for underpinning a house.
- Elevation survey
- A grid of relative floor-height readings across a house, producing a map of where it currently sits. The measurement every foundation inspection should produce.
- Stair-step crack
- Cracking that follows the mortar joints of brick veneer in a staircase pattern. The classic exterior signature of differential movement along one elevation.
- Sloping floors and sticking doors
- The two symptoms homeowners notice first indoors. A sloping floor shows the structure has moved; a sticking door that frees up again between seasons usually points at soil moisture rather than permanent damage.
- Drywall crack
- Interior cracking, typically diagonal from the corner of a door or window opening where stress concentrates. See foundation crack repair.
- Hydrostatic test
- A plumbing test that isolates and pressurises the drain lines under a slab to check for leaks. Worth doing before underpinning, because an unfixed leak keeps saturating the soil around new piers.
Where these terms show up
Most of them appear in the same two documents: the elevation survey a contractor produces during a foundation inspection, and the scope of work in the quote that follows it. If a quote uses a term that is not on this page and the contractor cannot explain it plainly, that is worth pausing on.
One term you will not find in a quote is the one that matters most commercially: who stands behind the work. That is covered in our disclaimer, and the short answer is the contractor, not us.
The mechanism behind nearly all of them — expansive clay changing volume with moisture — is covered in our guide to foundation repair across Texas. The repairs themselves are set out on the slab repair and pier and beam pages, and the water management that prevents most of it is on the drainage page.
If a quote does not explain itself
A scope of work should name the system, the number of piers and the target depth. “Install piers as required” is not a scope, and a contractor who will not put the detail in writing is telling you something.
If that is what you are holding, call and describe it. We will connect you with another independent licensed contractor so you have something to compare against.
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