Concrete Leveling Guide: Mudjacking vs Foam vs Replace

Last updated: October 27, 2026

What is concrete leveling and when do you need it?

Concrete leveling lifts a sunken slab back to grade without tearing it out. Think of a driveway section that dropped 1 to 2 inches, or a garage floor that slopes a quarter inch per foot toward the door. Or a sidewalk panel offset past the half inch that ADA guidance treats as a trip hazard. In almost every case like these, the concrete is fine. The dirt under it moved.

So leveling fixes height, not the surface. If the top is flaking, cracking, or coming apart, that’s a different job, and it starts in the concrete repair guide. Leveling won’t make a bad slab good. And the sooner you lift it, the better, because a slab bridging an empty space can crack from the strain.

Why did the slab drop in the first place?

The soil under the slab lost volume or washed out. That leaves a void, and the slab drops into it. Four causes cover most of it, and none of them are the concrete’s fault:

• Poor packing when it was built. This is the most common. The fill went in too fast, in layers that were too thick, and it kept squeezing down for years under the weight.
• Water. A downspout dumping at a slab edge, a yard that slopes the wrong way, or a slow plumbing leak can carry the soil out a spoonful at a time.
• Drought. Dry spells shrink clay soil until it pulls support out from under the edges.
• Tree roots. They draw water out of the ground in the dry months and do the same thing.

All four are still there after a lift unless someone fixes them.

You can often tell which one you have by walking around the house after a hard rain. A slab that dropped at one corner, right under a downspout, is a different story from a slab that dropped evenly across its whole face. Settling from poor packing shows up early in a slab’s life and then slows down. Settling from water keeps going, because the water keeps coming. Clay that moves with drought follows the seasons, and it often comes back up partway when the ground gets wet again. That’s why the same driveway can look worse in August than it did in April.

Settlement, heave, or a broken slab

These look alike at a glance, but they need opposite fixes. So naming the movement right is the first real step. Settlement is the slab dropping into a void where soil shrank or washed out. Heave is the reverse. The slab gets pushed up from below, almost always by expansive clay, which is clay that swells when it soaks up water. A structural crack is neither. It means the slab itself has broken through, often where it spans a void or carries a load nobody poured it for.

Get this wrong and you can make it worse. Pumping material under a heaved slab lifts a slab that’s already too high. Lifting a slab that’s broken into pieces just spreads the breaks. So we start at the low corner, follow the water, and watch how the cracks move under weight. Then we decide which tool comes off the truck.

How does mudjacking work?

Mudjacking, also called slabjacking, lifts a slab by pumping a slurry of cement, sand, and water into the void under it. The crew drills holes about 1.5 to 2 inches across through the slab. They pump the slurry in under pressure until the void fills and the concrete rises to grade, and then they patch the holes. The slab is ready for traffic in about 24 hours.

It’s the right call in three cases:

• Big voids under driveways, patios, and garage floors, where cheap fill matters most
• Slabs on firm soil that can carry the extra weight
• Lifts on a tight budget, where a patch 1.5 to 2 inches across is fine to look at

The downsides are the same two facts turned around. Cement slurry is heavy, and piling weight on soil that already failed to hold the slab up isn’t always smart. And the holes stay visible. On a back patio, nobody cares. On a stamped front walk, people do.

Where the holes go matters too. We place them to reach the void and to spread the lift across the whole panel. If one spot gets pushed up alone, the concrete around it cracks. That’s the difference between a slab that comes up in one piece and one that gets a new crack on the way to level.

How does polyurethane foam injection work?

Foam injection, or polyjacking, does the same job with a two-part polyurethane instead of slurry. Most crews reach for it when a lift has to be exact. The crew drills holes about 5/8 inch across, the size of a dime, and injects the resin. It reacts and grows within seconds, fills the void, and raises the slab. Then it cures hard enough for traffic in 15 minutes to an hour.

Two things make foam the better fit on a lot of jobs. First, cured foam weighs a fraction of what cement slurry weighs. So it doesn’t add real load to soft soil that’s already struggling. Second, we can control the reaction, so we bring the slab up evenly instead of in surges. That’s why foam suits walkways, garage floors, and any slab where a quarter inch too high would show. The small holes are easier to hide on a front walk, too.

The downside is material cost per cubic foot, which runs higher than slurry. On a small, exact lift you’ll barely notice. Over a big void it adds up fast, and that’s the job mudjacking was built for. Matching the method to the slab is the whole job, and it’s what a concrete leveling visit is for.

When does replacement beat lifting?

Three things push a slab past lifting and into tear-out:

• It’s broken into two or more sections that move on their own.
• The top is spalled or peeling away in layers, past what a surface repair can carry.
• The void and soil problem under it is too big to bridge with any injection.

Then the honest answer is to tear it out and pour new on a base packed to about 95 percent standard Proctor density. That’s the lab test for how tight soil should be packed. Replacement costs more on day one. A lift on a slab that keeps moving has to be done again, often every few years, while a slab poured on a good base has a 20 to 40 year life. The full trade-off, including where resurfacing fits in between, is in the overlay versus replacement guide.

Mudjacking vs foam vs replacement

A big driveway void over firm soil leans toward mudjacking on cost. A garage floor over soft fill leans toward foam on weight and precision. A slab broken into pieces leans toward replacement, whatever the other rows say. And both lifts last many years only if the soil gets fixed.

What concrete leveling cannot fix

Leveling changes height. It doesn’t change how the soil behaves. If the cause is still active, the slab will sink or heave again, and the material under it has nothing to do with it.

Expansive clay is the clearest case. It can swell with pressure over 3,000 pounds per square foot. That’s more than enough to undo a fresh lift in one wet season, and no slurry or foam can fight it.

So when we look at a slab, we check the water too, and the fix goes on the plan with the lift, not after it:

• The soil should fall at least 6 inches over the first 10 feet away from the slab. That’s about a 5 percent slope.
• The downspouts should empty past the slab edge, not at it.
• Where the clay itself is the problem, the clay needs work too.

ACI 302.1R covers how a slab on the ground needs to be supported. ASTM D698 is the standard Proctor test for packed soil. And the USDA NRCS soil survey will tell you what’s under your address before anyone guesses.

How do you choose a leveling method?

First, does the slab still move as one piece? If it does, it can be lifted. If it’s broken into sections that move on their own, no injection fixes that. Replacement is the answer, no matter how much cheaper the other choice sounds.

Once you know the slab can be lifted, four facts decide between slurry and foam: how big the void is, how much weight the soil can hold, your budget, and how long the slab can be out of use.

• Big void, firm soil, a tight budget, and you can wait a day: mudjacking.
• Soft soil, a lift that has to be exact, or a floor you need back this afternoon: foam.

Downtime is the one people underrate. A day off a back patio costs nothing. A day off the only driveway at a working shop, or off a garage floor with a truck that has to be in it tonight, is a real cost that just doesn’t show on the estimate. Foam that cures hard in 15 minutes to an hour is worth paying for on those jobs, and worth nothing on the others.

Leveling runs $4.72 to $9.38 a square foot with us, and our concrete leveling cost page shows what moves you inside that range. Size and site move the price the same way they do on any pour, and the concrete cost guide shows what really drives the number.

One last thing, because it’s the one people skip: fix the water. A lift on a slab where we found the cause can hold for years. A lift on one where nobody looked won’t. Finding out which one you have starts with the repair diagnostics.