The crew drills small ports in the settled slab and injects expanding polyurethane foam underneath. The foam fills the voids and raises the concrete back to grade in minutes. Traditional mudjacking uses a heavier cement slurry for the same purpose. The slab is usable the same day.
More detail
Concrete leveling raises a settled slab without tearing it out and repouring. The modern method is polyurethane foam jacking: the crew drills a series of small ports (about the diameter of a penny) through the slab, then injects a two-part expanding polyurethane foam through them. The foam flows into the voids beneath the slab that caused the settlement, expands, and lifts the concrete back to grade, and the crew controls the lift in real time by watching the slab rise. Foam is lightweight (so it does not add load to the soil that settled in the first place), cures hard within about 15 minutes, is waterproof, and the slab is typically usable the same day. The older method, mudjacking, pumps a cement-and-soil slurry through larger holes to float the slab up; it still works and can be cheaper for some jobs, but the slurry is heavy and the holes are bigger. Foam is the default for most residential work (garage floors, basement slabs, driveways, sidewalks, patios, pool decks, and settled front steps) because it is cleaner, lighter, faster-curing, and the small ports are easy to patch. Typical cost runs $500 to $1,800 depending on the size of the area and how much lift is needed. One caveat: leveling raises the slab, but if the slab settled because of an ongoing void-causing problem (eroding soil from a downspout, a leaking pipe, poorly compacted fill), that source should be addressed too, or the slab can settle again. We check for the cause during the assessment rather than just chasing the symptom.