Concrete leveling, including who is telling you which method to use

What is concrete leveling?

Concrete leveling raises a sunken slab back to its original height by injecting material through small holes drilled in the slab and filling the void underneath. Two methods dominate: mudjacking, which pumps a cementitious slurry, and polyurethane foam injection - often called polyjacking - which injects an expanding polymer. Both work. Which is better depends on the slab, the soil and the access, and almost nobody offering one of them will tell you when the other wins.

Signs you need concrete leveling

• A driveway, walkway or patio panel sits visibly lower than the one next to it
• There is a lip at a joint or a sidewalk section big enough to trip on
• A garage floor or apron has dropped away from the threshold and left a gap
• Water now pools on a slab that used to drain, or runs back toward the house
• Steps or a stoop have tilted and pulled away from the building
• A pool deck or patio slab has settled unevenly around its perimeter
• You can hear a hollow sound tapping parts of a slab, suggesting a void underneath

Seeing something not on this list? Browse concrete problems by symptom →

How concrete leveling actually works

1. 1

   Working out why it sank

   Slabs settle because something under them moved - soil consolidating under fill, a poorly compacted trench where a service was run, water washing fines out from beneath, or a downspout discharging next to the slab edge.

   Watch forA quote given without any discussion of the cause. Lifting a slab over an active erosion path buys you a year. The water source has to be found and dealt with, or the same panel drops again.

2. 2

   Assessing whether the slab is worth lifting

   The concrete itself has to be sound enough to be raised as a unit. A slab in a few large pieces can be lifted; one broken into many fragments or with a surface that is spalling apart cannot.

   Watch forA leveling quote on a slab that is genuinely at the end of its life. Lifting badly deteriorated concrete produces a level surface that is still failing, and the money would have gone further toward replacement.

3. 3

   Choosing the method honestly

   Mudjacking uses larger holes and a heavier slurry, and works well on thick slabs over reasonably stable soil. Foam injection uses much smaller holes, weighs very little, expands to fill voids, and is generally faster to return to service - which is why it dominates on driveways and around structures.

   Watch forA single-method contractor explaining why the other method is unsuitable in general terms. Ask instead what specifically about your slab and your soil favours their method. A vague answer is a sales answer.

4. 4

   Drilling and injecting

   Holes are drilled through the slab in a pattern, material is pumped through them, and the void beneath fills. Lifting is done gradually, in stages across the panel, so the slab rises evenly rather than being levered at one corner.

   Watch forLifting too fast or from too few points. Concrete has very little tensile strength and forcing a panel up at one point is a good way to crack it during the repair.

5. 5

   Monitoring the lift

   The technician watches the slab edge against a fixed reference, or uses a laser, and stops at the target height. Neighbouring panels and any adjoining structure are watched at the same time.

   Watch forNobody measuring against a reference. Over-lifting is a real risk, and a panel raised past its neighbours is a new trip hazard in the other direction.

6. 6

   Patching the holes and finishing

   Injection holes are filled with a cementitious patch. They remain visible as small circles, more noticeably with mudjacking's larger holes than with foam's.

   Watch forAn expectation that the repair will be invisible. It will not be. Level, safe and stable is the goal; cosmetically seamless is not what this repair delivers.

7. 7

   Joint sealing and drainage correction

   Open joints and cracks get sealed so surface water stops running into the base again, and the drainage that caused the settling is corrected - extending a downspout, regrading, or fixing a leak.

   Watch forJoint sealing skipped as a small extra. It is the cheapest part of the job and it is the part that stops water re-entering the void you just paid to fill.

What does concrete leveling cost?

Leveling is normally a fraction of the cost of replacing the same slab, which is the main reason to consider it. It is usually priced by the area lifted and the volume of material needed to fill the void. Foam injection typically prices higher per job than mudjacking. See the Cost Guide.

See the full concrete leveling cost guide - by material, size and region →

If the number is the problem, here are the ways people pay for it →