9 min read · Updated 2026-08-03
How to Lift a Concrete Slab, Step by Step
How do you lift a concrete slab?
A concrete slab is lifted by injecting expanding material through small holes drilled in the slab until it returns to grade. In modern polyurethane lifting, a technician drills 5/8-inch ports on a grid, injects a two-part structural foam that fills voids and compacts loose soil, monitors elevation with a laser as the slab rises, stops at grade, then patches the ports. Most residential slabs are done in one to four hours.
Key takeaways
- ✔Seven stages: inspect, measure, drill, inject, monitor, stop at grade, seal.
- ✔Ports are 5/8 inch — roughly the size of a dime.
- ✔Elevation is controlled with a laser, not by eye.
- ✔Foot traffic immediately; vehicle traffic about 15 minutes after the last injection.
Step 1 — Find out why the slab sank
Lifting a slab without diagnosing the cause is how repairs fail. Before anything is drilled, the slab gets walked and sounded for hollow areas, the perimeter gets checked for erosion channels, and downspouts, irrigation, grading, and nearby plumbing get inspected as water sources.
Around Murfreesboro the usual suspects are consistent: expansive clay that shrinks in drought and swells after rain, karst limestone that opens voids as it dissolves, and uncompacted construction backfill in newer subdivisions where trenches and foundation perimeters were never properly consolidated.
Step 2 — Establish grade with a laser
The target elevation gets set before the lift, not during it. A rotary laser or level establishes the reference line, the low points get measured against it, and the crew agrees on how far each area needs to travel.
This step also sets expectations. A slab that settled unevenly may not return perfectly flat without cracking, and it is better to know that on the driveway with a tape measure than halfway through an injection.
Step 3 — Lay out the injection pattern
Ports get planned so the polymer reaches every part of the void, not just the deepest dish. Typical spacing runs four to six feet on a grid, tightened near slab edges, joints, and corners where voids concentrate, and adjusted around anything embedded in the slab.
Good layout is why a professional lift stays flat. Injecting only at the low point levers the slab against its supported edge and cracks it.
Step 4 — Drill the ports
Holes are drilled at 5/8 inch, about the diameter of a dime. This is one of the practical advantages of polyurethane over mudjacking, which needs holes closer to one and five-eighths inches — visibly larger, and much harder to make disappear on a decorative surface.
Dust is controlled at the drill, and the holes get cleared so the injection gun seats cleanly against the slab.
Step 5 — Inject and watch the slab move
The two components travel through heated hoses and combine at the gun. They react on contact and expand within seconds. The first material to leave the gun does the unglamorous work: flowing into the void, finding the far corners, and compacting loose soil as pressure builds.
Only once the void is full does the slab begin to rise, and it rises slowly. The technician runs one port at a time in a sequence chosen to keep the slab moving as a plane, moving to the next port before any single point gets ahead of the others.
The laser stays on the slab the whole time. Lifts are stopped in fractions of an inch, and a good crew would rather come back to a port a second time than overshoot once.
Step 6 — Stop at grade and cure
Structural lifting foam reaches most of its strength within about fifteen minutes. There is no drying, no water to evaporate, and no waiting for a slurry to consolidate — the reaction is chemical, which is why cold weather does not stop the work.
The slab takes foot traffic right away. Vehicles can drive on it about fifteen minutes after the final injection.
Step 7 — Patch, seal, and clean up
Ports get filled with a cement-based patch tinted to blend with the slab. On a broom-finished driveway the patched dimes are hard to pick out from a standing position within a few weeks of weathering.
Cracks and control joints that were opened by the settlement get sealed, because leaving them open invites the same water back into the sub-base. Then the site gets cleaned — no spoil pile, no torn-up lawn, nothing to haul away.
What the process cannot fix
Lifting restores elevation and support. It does not restore concrete that has failed as a material. Slabs with heavy spalling, exposed and corroded rebar, or fracture into loose pieces should be replaced, and the inspection stage is where that call gets made.
It also cannot substitute for drainage work. If water keeps arriving under the slab, a new void will eventually form beside the treated one. Corrected downspouts and grading are part of the repair, not an upsell.
Related questions
How long does it take to lift a concrete slab?+
Most residential slabs take one to four hours from setup to cleanup. Larger driveways, pool decks, and commercial floors can take a full day, but they still open to traffic the same day.
How big are the holes for concrete lifting?+
Polyurethane injection ports are 5/8 inch, roughly dime-sized, and they are patched with tinted cement at the end of the job. Mudjacking requires holes around 1 5/8 inch.
Can concrete be lifted in cold or wet weather?+
Yes. The polymer cures chemically rather than by drying, so cold does not prevent a lift. Heavy active rain is a scheduling issue more than a technical one.
Will lifting a slab crack it?+
A controlled lift on a sound slab rarely causes new cracks, because the slab is raised as a plane with the load spread across many ports. Slabs that are already cracked will move along those cracks, which is why they are lifted in a deliberate sequence and sealed afterward.
How much can a slab be raised?+
Two to three inches is routine, and greater lifts are possible. Beyond a few inches the question shifts from 'can it be raised' to 'should it be' — very large drops often signal a deeper soil problem worth investigating first.