Can sunken concrete be raised instead of replaced?

What concrete leveling is

Concrete leveling (also called slabjacking or concrete lifting) raises a sunken slab by filling the empty space under it. A contractor drills holes through the slab, pumps material underneath under pressure, and lets that material lift the slab back toward its original height. The holes are then patched.

There are two main materials:

• Mudjacking uses a cement-based slurry, usually water, soil, sand and cement^[2].
• Polyjacking (foam lifting) uses expanding polyurethane foam. Once it cures, the slab sits on the foam^[1].

Both methods fix the same problem: a slab that dropped because the ground under it settled, washed out or shrank. Neither one fixes the ground itself. That is the single most useful thing to understand before you hire anyone. See why concrete sinks for the causes.

When raising beats replacing

Leveling is a good fit when all of these are true:

Check	Good for leveling	Better to replace
Slab condition	One piece, or a few large sound pieces	Shattered, crumbling, many small pieces
Direction of movement	Sank (low side is below its neighbor)	Heaved up (high side), or rocks under foot
Surface	Sound, maybe some hairline cracks	Deep scaling or spalling over large areas
Cause	Found and fixed (downspout, washout, fill)	Unknown or still active
Drop	Moderate	Very deep drops may cost more to fill than to repour[2]

HomeGuide's cost data puts mudjacking at $4 to $9 per square foot and full slab replacement at $6 to $15 per square foot^[2]. Polyjacking costs more: $8 to $25 per square foot on HomeGuide^[2], and $5 to $25 per square foot, about $15 on average, on Angi^[3]. So foam leveling is not always cheaper than tearing out and repouring a small slab. Get a replacement quote too when the job is a small walk or a single step.

Leveling also cannot lower anything. Injection pushes up. A slab that heaved, for example from tree roots or frost, needs grinding, cutting or replacement.

Mudjacking or foam: the quick version

	Mudjacking	Polyjacking
Material	Cement-based slurry	Polyurethane foam
Cost per sq ft	$4 to $9[2] ($3 to $6 on Angi[4])	$8 to $25[2] ($5 to $25 on Angi[3])
Hole size	1.5 to 2.0 in[2]	0.50 to 0.63 in[2]
Ready to use	About 24 hours[2]	About 15 minutes[2]
Weight on the soil	Heavy[2]	Very light[2]
Main risk	Can wash out if water keeps flowing under the slab[2]	Can over-lift if injected too fast[4]

Our full comparison, including what each method does badly, is at mudjacking vs polyjacking.

The lifespan myth

Search for "how long does mudjacking last" and you will see claims that mud lasts 1 to 5 years and foam lasts 10 to 15 years or "permanently." We could not find a published study behind either number. They come from contractor marketing.

What the engineering sources say is less exciting and more useful. The Foundation Performance Association, a Houston group of engineers, lists both mudjacking and foam injection as shallow repair systems affected by active, moving soil. Its list of reasons both fail is almost the same: changes in soil moisture, broken water or sewer lines under the slab, trees too close, extreme seasonal moisture swings and poor drainage^[1]. HomeGuide says properly done mudjacking lasts 5 to 10 years or longer and that longevity "depends more on addressing the underlying cause of settlement than on the mudjacking process itself"^[2].

In plain terms: the material under the slab rarely decides how long a lift lasts. The water and soil around it do.

What can go wrong during a lift

FPA's failure lists apply to both methods^[1]:

• Over-injection can bulge or crack the slab.
• Too much pressure can cause a blowout, where material breaks out the side or up through a crack.
• Material can enter cracked utility lines under the slab and partly or fully plug them. Ask the contractor how they locate and protect buried lines before drilling.
• Foam that is mixed too wet can let water seep into expansive clay before it hardens and cause local heave^[1].
• Mud can get trapped by roots, pipes or buried objects and give an uneven lift^[1].

A careful crew lifts slowly, watches the slab and its neighbors, and stops when the joint lines up.

Trip hazards: when a small drop matters

A slab does not need to sink far to become a hazard. FPA's guidance treats "vertical pavement offsets sufficient to cause tripping" as functional distress, a step above cosmetic^[5]. For a reference point, the federal ADA standards for public accessible routes allow a vertical change in level of only 1/4 inch. Changes over 1/4 inch up to 1/2 inch must be beveled, and anything more must be ramped^[7]. Those rules apply to public facilities, not your private walk, but they show how small a dangerous lip can be. If the low slab is a public sidewalk, check your city's rules on who must repair it before you hire anyone.

Leveling a house slab is a different job

Driveways, walks, patios, steps, garage floors and pool decks are flatwork. Your home's slab foundation is not. Foam or mud under a house slab is still a shallow fix in active soil^[1], and the drop you see is a symptom. In clay areas the soil may be shrinking in a drought and could swell back. Start with a structural engineer's evaluation before anyone injects under a house. Read how slab foundation repair works.

How to get a lift that lasts

1. Find the cause first. Look where water goes in a hard rain. Downspouts that dump next to a slab, gaps at the slab edge, and low spots that pond are the usual suspects. NRMCA lists poor subgrade preparation and missing joints among the main reasons slabs crack and move^[6].
2. Fix the water. Extend downspouts, seal the joint between the slab and the house, and regrade so water runs away.
3. Ask about the void. A good contractor explains how deep the void is and whether the fill will reach it.
4. Know your climate. In Ohio and Illinois, frost heave can lift slabs in winter and drop them in spring thaw. Frost heave needs three things: frost-susceptible soil, freezing temperatures that reach it, and water^[8]. Remove the water and you remove most of the problem. See frost heave.
5. Get the warranty in writing. Read what it covers. Many leveling warranties cover re-lifting the same slab, not new settlement from drainage you did not fix.

For surface-by-surface advice, see leveling by surface. For price ranges and what drives them, see concrete leveling cost.

When to call a pro

• A slab edge is more than about 1/4 inch above its neighbor where people walk, or a step has dropped.
• Water now flows toward your house instead of away from it because a slab tilted.
• A slab next to your house keeps dropping after you fixed the downspouts.
• You see cracks or sticking doors inside the house along with sinking outside: ask for a structural engineer before any lifting.