Concrete Slab Lifting

What slab lifting actually is

ACI defines slabjacking as "the process of either raising concrete pavement slabs or filling voids under them, or both, by injecting a material (cementitious, noncementitious, or asphaltic) under pressure." Holes are drilled through the slab, material is pumped through them into the space below, and the slab rises as that space fills.

Two details from the ACI field guide tell you most of what you need to know about the process. Lifting happens "in intervals no greater than 1/4 in. (6 mm) at any one hole location and at any one time, to avoid cracking," and once hole spacing and joint relief are right, working pressure under the slab settles to just "10 to 20 psi." This is a slow, patient, low-pressure operation carried out in tiny increments, not a hydraulic shove.

Holes go in roughly every 5 to 10 feet, with the ones nearest edges and joints set in 1 to 2 feet from them. A small sidewalk panel may need only one or two holes. Note the honest limitation ACI includes: if the finished appearance of the slab matters, lifting may be the wrong choice, because the patched holes stay visible.

The three methods, and how they differ

The weight argument, fairly stated. The main case made against mudjacking is that it adds hundreds of pounds of wet slurry to soil that has already proved it cannot carry what is on it. The foam numbers are solid: Alchatek publishes a free-rise density of 3 lb per cubic foot for AP Lift 430 and 4.75 lb for AP Lift 475, against ordinary concrete at roughly 150 lb per cubic foot. The slurry figures, though, come from HMI and Prime Resins, both of which sell polyurethane systems. No independent cost aggregator, industry body or academic source we could find publishes a slurry density at all. Treat the comparison as directionally right and commercially motivated at the same time.

What the foam data sheets do prove. AP Lift 430 reaches full strength in 15 minutes and is traffic ready in 15 minutes, with free-rise compressive strength of 50 psi rising to between 88 and 210 psi once confined under a slab. AP Lift 475 gives 110 psi free rise and up to 406 psi at triple confinement. Both displace water, which is why foam is the usual answer when the void under the slab is wet.

What slab lifting costs in 2026

There is no industry body or government source for this. Every figure below comes from a cost aggregator, and they disagree in ways worth knowing about.

Per square foot. HomeGuide puts mudjacking at $4 to $9 and polyjacking at $8 to $25. Angi and HomeAdvisor both start mudjacking at $3 and cap it at $6 to $8, with polyurethane at $5 to $25. Fixr is the outlier at both ends, quoting mudjacking from $3 all the way to $25 and polyurethane at $20 to $25. Angi even contradicts itself: its concrete leveling article says mudjacking runs $3 to $6, while its mudjacking article says most companies charge $3 to $8.

Per project. Angi reports a national average of $1,235 drawn from 2,631 verified projects, with a typical range of $661 to $1,874 and labor at 50 to 70 percent of the total. HomeAdvisor publishes the same numbers, which is unsurprising since Angi owns it, so treat them as one source rather than two. Fixr averages $1,500. Thumbtack, which reflects quoted bids rather than completed jobs, runs two to three times higher at $902 to $3,232. Expect a minimum service fee of $300 to $700 whatever the size of the job.

The comparison nobody makes. Lifting is usually quoted as a third to a half the cost of replacement, and for mudjacking that holds. But tearing out and replacing a slab runs $8 to $18 per square foot including disposal, and polyurethane at the top of its published range is $25 per square foot. On a small job, where per-square-foot foam pricing is highest, foam can cost more than a new slab. Price both. The concrete slab cost calculator will give you the replacement number for your own dimensions, and the slab cost guide breaks down what drives it.

Is your slab a candidate?

The short version: lifting suits a slab that has dropped but is otherwise sound. It is the wrong repair for a slab that is falling apart.

Good signs. The slab has settled as a unit, the concrete itself is in decent shape, and there is a void underneath. This Old House gives the clearest published threshold: a slab that "has sunk no more than eight inches and is otherwise in good condition, so not cracked or broken" is a candidate. You do not need to clear the slab first either, since the pump lifts the slab and whatever is sitting on it.

Bad signs. HomeGuide rules out concrete with "extensive cracking (wider than 1/4 inch), significant spalling or surface damage," or that is severely deteriorated. A quarter inch of crack width is the most useful single number here. Practitioners add that a slab broken into many small pieces cannot hold pressure at all, that the material simply oozes out through the breaks, and that lifting cannot fix spalling, flaking or dips that were troweled into the original pour, because the work happens from underneath. Those specifics come from contractors rather than a standards body, so weigh them accordingly, but the physics behind them is sound.

Two more disqualifiers. Fixr says to avoid mudjacking where the slab is thicker than six inches, which we found nowhere else, so treat it as one opinion. And ACI notes that where settlement is still happening, "it may be necessary to repeat the slabjacking one or more times."

Has it settled, or has it heaved?

This is the question that decides whether lifting helps or makes things worse, and almost nobody asks it. Lifting a slab that has risen pushes it further out of plane, and you cannot bring it back down.

Wallace Design Collective, a structural engineering firm, sets out a diagnosis a homeowner can follow. Start by walking the building and finding an area of slab "that looks as though no vertical movement has occurred," because you need a datum before you can say which way anything moved. A laser level survey then tells you whether the surrounding slab has risen or fallen.

Their neatest test uses the trim. If the finish material at a roof-supported soffit is moving up relative to a slab-supported wall, settlement is the likelier cause. If roof-supported finish is moving down relative to slab-supported material, heaving is likelier. The causes differ too: settlement follows deep fill consolidating after construction or sandy soil washing away, while heave comes from expansive soils taking on moisture from a high water table, failed pavement sealants or "even small leaks in underground plumbing lines."

A slab that rises in winter and settles back in spring is moving seasonally rather than settling, and locking it at its winter elevation is not a repair. And if movement is suspected at all, Wallace's advice is to engage a structural engineer, who can say whether what you are looking at is cosmetic, structural or a life safety issue.

Fix the cause, or pay twice

Go back to the ACI sentence at the top of this page. Lifting restores elevation. It does nothing about why the support disappeared. If water is still running under the slab, the void will come back.

The cost aggregators price the companion work as separate line items, which tells you how routine it is: Angi lists drainage improvements at $300 to $1,000 and soil stabilization at $500 to $2,000, and HomeGuide puts both at $500 to $2,000 or more. Angi is explicit that polyjacking "can be a permanent solution to sunken concrete if you also address the underlying issue."

Practically, that means looking at where water goes before you book anyone: downspouts discharging beside the slab, grade falling toward the house rather than away, a sprinkler line or supply line leaking under the driveway. We should be straight that the downspout and grading advice is practitioner guidance rather than a cited standard. The principle behind it, that lifting does not correct soil conditions, is ACI's.

How long it lasts, and what to ask about the warranty

HomeGuide gives the cleanest independent contrast: mudjacking lasts 5 to 10 years or longer, polyurethane 10 to 15 years or longer. Bob Vila puts concrete leveling generally at 5 to 10 years while noting some jobs do not make it that far.

Warranty practice is a different matter. No independent source publishes typical terms. The figures circulating (five years on one major foam system, ten years from some foam contractors, often nothing at all for mudjacking) come from companies that sell foam, and at least one of them is a dealer for the system it recommends. So rather than repeat a number, ask the questions:

• If the area settles again, is re-lifting covered, and how many times?
• Is there a cap on re-lifts hidden inside a lifetime warranty?
• Is the warranty transferable if you sell?
• Does it depend on you also buying joint or crack sealing?
• What are the exclusions, and does further soil movement count as one?

One contractor we reviewed is candid that the industry contains "lifetime warranties with one re-lift caps" and three-year terms loaded with restrictions. Read the document, not the headline.

Slab lifting is not self-leveling underlayment

These two jobs share the phrase "concrete leveling" and have nothing else in common.

Slab lifting works under the slab. Material is injected into the voids below and the existing slab rises. Nothing is added on top and the floor level returns toward where it started.

Self-leveling underlayment works on top of the slab. A cementitious mix is poured over the floor to create a flat plane, and the slab itself never moves. Mapei's own definition is precise: an underlayment is "formulated for leveling, smoothing and providing a flat surface prior to the installation of tile, stone, VCT, wood flooring, resilient and other floor coverings, and must be covered," and is for interior use only. A topping, by contrast, is a wear surface meant to be left exposed.

The confusion is not the reader's fault. Angi, HomeGuide and Fixr all list self-leveling compound in the same per-square-foot table as mudjacking and polyjacking under the heading "concrete leveling," so the term genuinely covers both. Meanwhile Concrete Network's own guide to leveling interior concrete floors covers patching, self-leveling overlays and grinding, and never mentions slabjacking once. If your floor is flat but sitting too low, you want lifting. If your slab is at the right elevation but the surface is dished or sloping under a finish floor, you want an underlayment: see self-leveling underlayment and the self-leveling concrete calculator, or how to level a concrete floor for the interior decision as a whole.

Why this is not a DIY job

We looked for consumer lifting kits at the big retailers. What actually comes back for searches like "concrete lifting foam" is a different product category entirely: post-setting foam for fence posts, polyurethane joint sealant, and self-leveling underlayment. None of those lift a slab. The only genuine slab-lifting equipment sold online is contractor grade, built on heated plural-component spray rigs.

The technical case against DIY comes from primary documents rather than from contractors defending their market. Alchatek's data sheet calls for the A side at 100°F, the B side at 110°F and heated hose at 105°F, with a cream time of 2 seconds and tack free at 17 seconds. That is a two-second working window on temperature-controlled equipment. Pair it with ACI's instruction to lift in increments no greater than a quarter inch per hole per pass and you have a process that cannot be controlled with a canned product.

The failure modes practitioners describe follow from that: foam pancaking under the slab instead of filling the void, a new hump where there used to be a dip, cracked slabs from holes in the wrong places, and over-lifting, which is unrecoverable because once the slab is too high you cannot bring it back down. This Old House recommends hiring a professional and notes that mistakes can damage the concrete or injure you. No independent source we found endorses DIY slab lifting, which is itself the finding.

When to replace instead

Replacement wins when the slab is beyond saving, when appearance matters more than budget, or when the numbers converge. Concrete removal runs $3 to $8 per square foot including disposal, with dump fees of $90 to $160 per ton, and a full tear out and replace is $8 to $18 per square foot. Against that, budget mudjacking at $3 to $9 and understand that foam can reach $25.

The trade-off beyond money is time. A replacement slab has to cure, and full cure is 28 days, though you are walking on it long before that. Lifting puts a driveway back in service the same day, and foam in about fifteen minutes. Our concrete cure time guide covers what those waiting periods actually mean.

If replacement is the answer, size it properly: the concrete slab calculator gives cubic yards and bag counts from your dimensions, slab thickness covers how thick to pour it this time, and rebar and reinforcement covers what goes inside. For a driveway specifically, concrete driveway cost itemizes a new pour and driveway resurfacing cost weighs lifting against resurfacing and replacement, which is the comparison you are actually making if the slab has dropped. And read how to pour a concrete slab for the base preparation that stops the new one settling the way the old one did.

When a sunken slab becomes a legal problem

If the slab is a public walkway or a path customers use, there are numbers that turn this from a nuisance into a liability.

The 2010 ADA Standards set out exactly where an abrupt edge stops being acceptable. Changes in level up to a quarter inch high may be vertical. Between a quarter inch and a half inch they must be beveled no steeper than 1:2. Anything greater than a half inch "shall be ramped." So a quarter inch is the point at which a lifted or dropped edge falls out of compliance, and a half inch is the point where beveling no longer helps.

Municipal codes put money behind it. New York City defines a trip hazard as a vertical grade differential between adjacent sidewalk flags "greater than or equal to one half inch," and also names an undermined flag with a visible void beneath it, or one that rocks or seesaws, as a defect. Property owners there are responsible for the sidewalk adjoining their property. That is New York's ordinance rather than a national rule, and thresholds vary by city, but a rocking flag over a void is the textbook lifting candidate.