Slabjacking and Foam Lifting for Settled Concrete

The panel outside my garage door dropped about three quarters of an inch over four winters, enough that the lip caught the front of my wife’s car every time she pulled in. My first instinct — and it is the instinct that gets homeowners into trouble — was to rent a jackhammer and replace the panel myself over a long weekend. A guy who does concrete for a living talked me out of it in ninety seconds, and not for the reason I expected.

He asked what made it drop. I did not have an answer. That turned out to be the whole issue.

Lifting only works on concrete that is otherwise fine

The idea behind both slabjacking and foam is the same: the slab is not broken, it is no longer sitting on anything. Something washed out or compressed underneath, leaving a void. Rather than demolishing good concrete, you drill small holes through it, push material underneath, and float it back up to grade.

That works when the panel is sound — one settled section, joints still tight, maybe a single crack. It does not work when the slab is crumbling, spalled through, cracked into pieces, or rocking underfoot. You cannot lift rubble, only rearrange it. Ours qualified, barely. If yours does not, the honest answer is in when a driveway is past saving, and I would rather someone read that than spend $1,400 on concrete with two years left.

The two methods, and what they cost

Mudjacking is the older method. A crew drills holes around 1 5/8 to 2 inches across and pumps in a slurry of cement, sand and sometimes soil until the slab rises. Patched holes stay visible as gray dots. Pricing runs $3 to $8 per square foot, so a couple of settled panels land near $500 to $1,500. The catch is weight: that slurry runs over 100 pounds per cubic foot, so you are loading soil that already failed, and it can wash out if running water caused the void.

Polyurethane foam lifting drills much smaller holes, around 5/8 inch, and injects two chemicals that expand in place. Cured density is only 2 to 4 pounds per cubic foot, so it fills the void without loading the soil, and it does not absorb water. It sets in minutes — you can usually drive on it within the hour, versus 24 to 48 hours for mudjacking. It costs more: $8 to $25 per square foot, roughly $1,200 to $3,000 for a driveway section. I paid at the high end and would again, because our problem was water.

Both repair elevation, not strength. The American Concrete Institute publishes guidance on evaluating and repairing existing concrete at concrete.org, and the theme running through it is that you fix the cause before the symptom.

Why I did not do it myself

I looked. There are DIY foam kits sold for garage floors, and I ran the numbers twice hoping they would work. Cost killed it first: a kit big enough to matter runs $400 to $900 and yields a few hundred board feet, which sounds like plenty until you realize a 10 by 10 panel over a one inch void needs close to that by itself. Then the line that stuck with me: you cannot un-lift it. The foam expands hard, and a quarter inch too far cracks the panel you were trying to save. The professional version is not about the material, it is about someone watching a laser level and knowing when to stop.

Fix the reason first, or you will pay twice

Concrete does not sink because it got heavy. Something under it moved. In our case the downspout on that corner dumped onto the ground eight inches from the slab edge, and four spring melts had carried the base out from under it. Extending that downspout cost $40 and an hour. That was the actual repair. The foam was cleanup.

The usual suspects, in the order I would check them:

Roof water. Downspouts discharging next to a slab edge. Extensions are $25 to $150 each, or $150 to $500 to bury a run to daylight.
Fill that was never compacted. Common beside a foundation, where trench backfill settles for years. Nothing you can fix from the top.
Expansive clay. The bentonite clay and claystone under the Front Range swells wet and shrinks dry, so slabs here rise as well as drop. Lifting one riding a moisture cycle is a temporary win.
Deep frost. Our frost depth runs near 30 inches, and a poorly drained base has plenty to work with over a hundred-odd freeze-thaw cycles a year.
A leaking irrigation line or sewer lateral. Rare, and the fastest sinking of the bunch.

Frequently asked questions

How long does slab lifting last? Indefinitely, if the cause was fixed — the material itself does not decay. If running water caused it and nothing changed, mudjacking slurry can wash out in a few years and even foam will sit there while the soil around it keeps moving. Ask the estimator what they think caused it. If they have no theory, keep calling.

Is lifting cheaper than replacing? Usually a third to half the price. Replacing a driveway section runs $10 to $18 per square foot installed, against $3 to $25 for lifting depending on method. The exception is a badly cracked slab, where lifting buys a short delay. Where the settled slab sits under an enclosure the maths changes again — a Long Island sunroom builder would rather lift than rebuild a room around a new slab.

Will the holes show? Yes, on both methods, though foam holes are small enough to miss after a season of dirt. Patch color rarely matches aged concrete. If appearance is the main reason for the work, know that before you sign.

Code reference: International Code Council.