Slab Foundation Repair in Montgomery County, Alabama

Settlement and heave are opposite problems

Settlement is the slab going down: soil beneath the footing or the interior fill loses volume or washes out, and a section of the house follows it. Heave is the slab going up, and in central Alabama it is usually a moisture story. Smectite-rich clays derived from the Selma Group chalk swell when they take on water and shrink and crack open when they dry. The Alabama Cooperative Extension System describes these Black Belt clays plainly: they shrink and crack when dry and swell when wet.

A slab that has heaved in the middle and a slab that has settled at a corner can produce similar-looking drywall cracks. They call for opposite fixes. This is the single most consequential distinction in slab repair, and it is why elevation readings matter more than a visual once-over. Underpinning a heaving slab does not address the mechanism and can make the differential worse.

How slabs get stabilized

Underpinning is the usual structural answer, and there are two common systems plus one non-structural technique.

Steel push piers are hydraulically driven in sections through the unstable layer to a firm bearing stratum, using the weight of the structure itself as the reaction force. Because the house provides the resistance, the achievable depth depends partly on how heavy that section of house is, which is why push piers work well under load-bearing exterior walls and less well under light structures. The load is transferred to brackets fixed at the footing once bearing is reached.

Helical piers are screwed into the ground with a hydraulic torque head, and the installation torque correlates with capacity, so the target is a torque value rather than purely a depth. They do not need the structure's weight to install, which makes them useful under lighter loads, on additions and porches, and where access is tight.

Polyurethane injection is not underpinning. Where the perimeter footings are sound but interior fill beneath the slab has consolidated or washed out, leaving a void, expanding polymer injected through small ports fills the void and can lift the slab back. It addresses interior voids, not failed bearing at the footings.

Lift is a negotiation, not an absolute

Recovering full original elevation on an old slab can crack finishes, break rigid plumbing and split brick that have long since settled into their current positions. Every inch of recovery is stress reintroduced into a structure that has already adapted. A contractor who talks about stabilizing first and recovering elevation second is usually reading the house correctly, and one who promises a perfectly flat floor on a forty-year-old slab is promising something that may cost you more in finishes than it gains in level.

The reasonable conversation is about how much differential will be recovered, over how many stages, and what interior damage is expected. Get that in writing before work starts, including who is responsible for repairing drywall, tile and trim afterward.

Local factors that speed a slab problem along

• Plumbing leaks under slab, which soften subgrade continuously and quietly
• Poor perimeter drainage in a county that averages roughly 52 inches of rain a year
• Late-summer drying, when September and October typically run driest and clay pulls away from footings
• Fill placed on sloping lots during the region's suburban expansion
• Large hardwoods within a canopy width of the foundation
• Irrigation running heavily on one elevation and not the others
• Post-tension or conventionally reinforced slabs with corroded or inadequate reinforcement

Rule out plumbing before you underpin

An under-slab supply or drain leak is one of the few causes of slab movement that gets worse regardless of the weather, and it is the one most often missed. It quietly saturates the subgrade beneath one part of the house, softening bearing soil in settlement-prone ground or feeding swell in expansive clay, and it will keep doing so after piers are installed.

A static pressure test on the supply lines and a hydrostatic test on the drain lines are inexpensive relative to a pier job. If the movement is localized near a bathroom, a kitchen, a laundry or a water heater, or if the water bill has changed, testing before committing to structural work is the sensible order.

What a serious proposal contains

A slab proposal worth comparing names the pier type, the exact count, the spacing, the target depth or installation torque, the expected lift, and what happens to interior finishes. It should identify what the contractor believes caused the movement. It should state what is being done about the water, because piers hold a house up but do not stop the soil cycle that moved it. And it should say what is excluded, which is often where the surprises live.

What drives the cost

Without quoting prices, the variables that move a slab repair number are: the number of piers, which follows from how much of the perimeter is affected; the depth required to reach competent bearing, which varies enormously across this region; access, since a pier location behind a deck, a patio or mature landscaping costs more to reach; whether interior piers are needed, which means cutting the slab; how much lift is being attempted; and whether drainage correction, plumbing repair and finish repair are inside or outside the scope. Two quotes can differ by a wide margin honestly, purely on scope.

What is fair to expect afterward

Slab repair is disruptive work and the honest version of it includes some collateral damage. Excavation at pier locations disturbs landscaping and hardscape. Interior piers require cutting and patching the slab. Lift reintroduces stress into finishes, so some drywall cracking, tile movement or door adjustment is normal rather than a sign something went wrong. What matters is whether that was disclosed beforehand and who is responsible for putting it right.

Ask specifically: will the excavations be backfilled and compacted, or just filled? Will the sod, shrubs or pavers be restored, and to what standard? Who repairs the drywall and repaints? Will interior doors be re-hung if they no longer latch after the lift? None of these are unreasonable to ask, and the answers should be in the written scope rather than settled by argument once the equipment is on site.

Find out what kind of slab you have

Not all slabs are built the same way, and the difference matters before anyone drills into one. A conventionally reinforced slab contains steel reinforcing bar or welded wire mesh and can generally be cored or cut with normal precautions. A post-tensioned slab contains high-strength steel tendons stressed after the concrete cured and held under considerable tension by anchors at the perimeter.

Cutting a post-tensioned tendon is dangerous and expensive. Post-tensioned slabs are usually identified by a stamped or placarded notice at the garage or on the slab edge, and any interior pier work, plumbing repair or coring on one needs a tendon scan first to locate the cables. If you do not know which kind you have, say so, and expect a competent contractor to establish it before proposing interior work.

It affects the repair strategy too. Post-tensioned slabs are designed to behave as a stiff plate and generally tolerate perimeter underpinning better than they tolerate interior penetrations, which pushes the design toward perimeter piers and exterior drainage rather than interior work.