The short answer: Foam lifting can raise an eligible settled slab by filling space beneath it and lifting in controlled stages. The slab, soil support, drainage and connected structures determine whether to lift, fill a void or recommend a different repair.
Why the slab dropped in the first place
A concrete slab is a thin, stiff plate sitting on dirt. It carries weight well only while the ground beneath it holds still. When soil leaves one area, that part of the slab sags, tips, or breaks off along a joint.
Water is the usual culprit. A downspout emptying at the driveway edge, a sprinkler soaking the same strip nightly, or a slow line leak carries fine soil away. Loose fill settles under its own weight. Clay swells when wet and shrinks as it dries, and some dry soils around New Mexico and El Paso compact suddenly once soaked.
Before anything gets drilled
The job starts with a walk around the slab with you. We ask when you noticed the drop, where rain and sprinkler water go, and what the concrete carries. We look at cracks, joints, washed-out edges, and whatever ties into the slab: steps, a footing, pool coping.
Then we measure how far each part has sunk and pick a target: level with the next panel, back up to the door threshold, or a gentle fall that sends water away from the house. Next we mark injection points that cover the low area and keep clear of joints, drains, and buried lines. Tell us about any pipe under the slab.
- Show the whole slab as well as the uneven joint or low area.
- Describe when the drop appeared and where water flows after rain.
- Identify known pipes, drains, electrical lines and anything attached to the panel.
- Agree on the lift target, limits, visible patches and return-to-use instructions.
What the foam does under the slab
Access takes a handful of dime-sized holes drilled through the concrete. Nothing gets sawed out or hauled away. A nozzle seats tight in each hole so the foam is pushed down under the slab instead of back out at us.
The foam arrives as two liquids that combine in the gun, then react, expand, and harden under the slab. Expanding foam takes the easiest path, so it fills empty pockets first. Once the pockets are full, the pressure starts to lift the slab. Cured foam is light, so it adds little weight to ground that already failed.
How the rise is kept under control
Foam pushes hard, and concrete barely bends, so we inject in short shots and watch the slab before adding more. The soil, the panels beside it, and anything tied to the slab all resist, so the first shots may show nothing before the slab starts to come up. Short shots keep that rise gradual.
We judge the lift by the concrete, not a pressure reading: a level across the joint, the gap at the door, the line of the pool coping, the fall toward a drain. We stop at the target, or sooner if pushing further would crack the slab or bind something attached.
Small patches and a slab back in use
When the lift is done, each hole gets patched and we clean up. You are left with a short row of small circles. Fresh patch never quite matches concrete that has spent years in the sun, so you can find them if you look.
The crew gives return-to-use instructions for the work performed. Foot traffic, vehicles, trailers and heavy equipment can have different limits, depending on the product, slab condition and movement. Confirm those instructions before using the area.
Lifting, mudjacking or new concrete
Foam lifting and mudjacking both work beneath an existing slab. Foam expands after injection; mudjacking pumps a cementitious slurry into the space. The access, material, support conditions and target should be compared in the actual scope.
Replacement removes the slab and rebuilds it. It may be appropriate when the concrete is badly deteriorated, the layout or reinforcement must change, or raising the existing slab would leave an unsuitable slope or connection. Return-to-use instructions depend on the selected method and work.
- Compare which panels are included and the intended final height or drainage slope.
- Ask how the underlying cause, unknown voids and connected structures will be handled.
- Confirm access holes, patch appearance, cleanup and when each area can be used.
| Method | Work at the slab | Important limit |
|---|---|---|
| Polyurethane | Inject expanding foam beneath concrete that can be retained. | Raising it does not repair deterioration or rule out future soil movement. |
| Mudjacking | Pump a cementitious mix beneath the existing panel. | Material weight, access and support conditions need review. |
| Replacement | Remove and rebuild the slab and its support as specified. | Scope, drainage, finish and curing requirements differ from a lift. |
What lifting cannot fix
Foam fills space and moves concrete. It does not stop water, mend broken concrete, or hold back a shifting foundation. If whatever washed the soil out is still at work, the slab will drop again, which is why the cause comes first.
Some of that is a plumber’s or a landscaper’s job before we show up, and a moving foundation calls for a different repair. A lift done after the cause is handled tends to stay put. What stops a lift from being the right call:
- A water line, pool, or sprinkler leak that is still running
- Concrete that is shattered or crumbling
- A house foundation that is still moving
- Roots, erosion, or a grading problem that started the drop
Further reading
In short
- Slabs sink when the soil beneath washes out, settles, or shrinks, so find the cause first.
- A foam lift needs only a few dime-sized holes; the foam fills the gap before it raises anything.
- The rise comes in small shots, checked against the next panel, the door, and the drains.
- The patches remain visible; the crew confirms when the slab can carry foot traffic and vehicles.
- Lifting will not stop a leak, rebuild broken concrete, or steady a moving foundation.