A sunken slab almost never means bad concrete — it means the soil underneath moved, washed out, or was never compacted in the first place. That’s the whole logic of concrete leveling: instead of demolishing a structurally sound slab that’s merely sitting in the wrong place, you pump material beneath it and float it back to grade for a quarter to half the cost of replacement. The industry does this two main ways, mudjacking and polyurethane foam injection, and choosing between them — or recognizing the slabs that shouldn’t be lifted at all — is where homeowners either save thousands or throw money at concrete that was already condemned. Here’s how each method works and how to make the call.
- Why Slabs Sink in the First Place
- Mudjacking: The Original Method
- Polyurethane Foam Lifting: The Modern Standard
- What Concrete Leveling Costs vs. Replacement
- When Leveling Works — and When It's Money Wasted
- Slab Lifting vs. Self-Leveling Underlayment
- After the Lift: Making It Last
- Hiring It Out: Questions That Sort the Pros
Why Slabs Sink in the First Place
Concrete follows its base. Builders routinely backfill around foundations loosely, and over 5 to 15 years that fill consolidates, leaving the sidewalk, stoop, or garage-adjacent driveway slab hanging over a void until it settles into it. Erosion is the other big driver — a downspout dumping at a slab corner can wash out a cavity in a few seasons, and a leaking irrigation line does it invisibly. In clay-soil regions, slabs also ride the shrink-swell cycle, dropping during droughts. Identify the cause before lifting, because a slab leveled over an active washout will sink again; the downspout extension or grading fix is part of the repair, not an afterthought.
Mudjacking: The Original Method
Mudjacking — also called slabjacking or pressure grouting — drills 1-5/8 to 2-inch holes through the slab, then pumps a slurry of sand, water, and Portland cement underneath at low pressure. The slurry fills voids first, then, as it packs, hydraulic pressure lifts the slab. A crew levels a typical driveway section in two to four hours, patches the holes with mortar, and the slurry cures hard within 24 to 48 hours; light foot traffic is fine almost immediately, vehicles usually the next day.
Cost runs $3 to $8 per square foot, with typical jobs between $500 and $1,500 — a sunken sidewalk panel might be $300, a two-car driveway slab $900. The weaknesses are the holes (big enough to notice forever) and the weight: cement slurry adds 100+ pounds per cubic foot on top of soil that already proved it can’t hold what it had. On slabs over poorly compacted fill, mudjacked concrete re-sinks often enough that reputable companies warranty the work for only 2 to 5 years. It remains a fair choice for heavy slabs needing big lifts on stable soil, and it’s usually the cheapest bid on the table.
Polyurethane Foam Lifting: The Modern Standard
Polyjacking injects a two-part expanding polyurethane through 5/8-inch holes — closer to a wine-cork than the mudjack’s silver-dollar penetrations. The components react under the slab within seconds, expanding up to 15 to 25 times their liquid volume and generating controlled lifting force. The foam cures in about 15 minutes to a rigid, water-resistant fill weighing only 2 to 4 pounds per cubic foot, so it adds essentially no load to the failed soil below. Crews can feather slabs up in 1/8-inch increments with real precision, and you can drive on the work the same afternoon.
Expect $5 to $12 per square foot, typically 20 to 40 percent more than mudjacking for the same job — $800 to $2,500 for common residential projects. National franchise networks (PolyLevel via Foundation Supportworks dealers, Thrasher, and many independents running HMI or Alchemy-Spetec rigs) dominate the space, and warranties of 5 to 10 years are standard because re-settlement rates are genuinely lower. The material’s one caveat: verify the installer uses closed-cell, hydro-insensitive foam rated for below-grade use, which shrugs off groundwater instead of degrading in it. On jobs where the void is enormous — say a washout under a garage apron measured in cubic yards — some crews fill the bulk with slurry, then finish and fine-level with foam.
What Concrete Leveling Costs vs. Replacement
The math is why the industry exists. Tear-out and repour of a driveway runs $8 to $15 per square foot once demolition, disposal, base prep, and finishing are counted, and the new slab needs 7 days before it takes a car and 28 to reach full strength. Leveling the same slab costs $3 to $12 per square foot, happens in a morning, and keeps 30-year-old concrete that — cosmetics aside — is often better cured and harder than what would replace it. On a 400-square-foot driveway, that’s roughly $2,000 to $4,000 in leveling versus $4,000 to $6,000-plus to replace. Leveling wins whenever the slab itself deserves to be saved.
When Leveling Works — and When It’s Money Wasted
Good candidates share a profile: structurally intact slabs sunk 1/2 inch to about 2 inches, cracked into a few large pieces at most, with a correctable cause underneath. Sidewalk trip hazards, settled patio and pool-deck sections, sunken porch stoops, and driveway panels dropped at the garage apron are the bread-and-butter jobs, and lifting restores drainage slope as a bonus — often the real reason water has been pooling against the foundation.
Walk away from lifting when the slab is crumbling, scaled, or shattered into many small pieces — the injection points and lifting stresses will just break it further, and you’d be pumping money under junk. Slabs heaved upward by tree roots or expansive clay can’t be fixed by a process that only pushes up. Severely sunken concrete (3+ inches) can sometimes be lifted but often signals soil problems big enough to justify engineering eyes first. And a slab poured over organic fill or trash — you’ll know because it keeps sinking after a previous lift — needs the soil problem solved, sometimes with deep compaction grouting or piers, before any surface fix will hold.
Slab Lifting vs. Self-Leveling Underlayment
One naming collision trips up a lot of homeowners: the bagged “self-leveling concrete” at the hardware store is not this. Self-leveling underlayment (Ardex, Mapei, LevelQuik) is a flowable cement product poured in thin lifts over an interior floor to flatten it before tile or flooring goes down — it fixes the top surface of a slab that stays where it is. Concrete leveling in the mudjacking/polyjacking sense moves the entire slab by treating the soil problem underneath. If your garage slab has settled 2 inches at the door, pouring leveler on top just adds weight and a bond line; the slab needs lifting. Conversely, if a basement floor is wavy but hasn’t moved, injection lifting is the wrong tool and a $40 bag of underlayment is the right one. Match the fix to whether the slab has actually displaced.
After the Lift: Making It Last
The repair’s lifespan mostly depends on what you do about water in the first month afterward. Extend downspouts at least 6 feet past the slab, correct any grading that sends runoff along slab edges, and caulk the joints — the crack between driveway slabs and the joint against the garage apron are the main infiltration paths, and a $8 tube of self-leveling polyurethane joint sealant (Sikaflex or NP1) closes them. If the slab was lifted, the old cracks remain; fill them so they don’t feed water to the soil you just stabilized. Re-inspect after the first hard rain and the first winter. A leveled slab with managed water routinely holds for 10 to 20 years; the same slab with a downspout still discharging at its corner can be back on the schedule in three.
Hiring It Out: Questions That Sort the Pros
Concrete leveling is not a DIY trade — the pumps, materials, and judgment about where pressure goes are the whole job — so vetting the contractor is your quality control. Ask four things. Which material, and why, for your specific soil and slab? (A company that offers only one method will recommend that method every time.) What’s the lift plan — injection points, target elevations, and how they’ll protect nearby slabs from unintended lifting? What caused the settlement, and does the quote address it? And what does the warranty cover — re-settlement to what tolerance, for how long, transferable or not? Get two or three bids; pricing spreads of 50 percent on identical work are common in this trade. Done by a good crew on the right slab, concrete leveling is one of the highest-return repairs in home ownership — an hour of pumping that erases a decade of settling.
