Quick answer
Mudjacking, also called slabjacking, is a repair that raises a settled concrete slab by drilling holes through it and pumping a cement-based slurry beneath it, so the slurry fills voids and pushes the slab back up toward its original level.
It lifts and fills. It does not add deep support under footings, and it does not remove the reason the soil settled. Work on a slab that is part of a house structure should involve an engineer.
Quick facts
The key facts about Mudjacking, with sources:
- Also called
- Slabjacking, concrete leveling 1
- Material
- Cement-based grout, such as a pozzolan, flyash or limestone mix 1
- Access
- Holes drilled through the slab; ODOT describes 2 to 3 inches for conventional grout 2
- Limit on each lift
- FHWA advises raising a slab no more than a quarter inch at a time at each hole 1
- Best fit
- Localized settlement in a slab that is otherwise free of cracking 1
- Price
- Not quoted here; see the cost drivers section
Key takeaways
- Mudjacking lifts a concrete slab by pumping cement-based grout through holes drilled in it.
- It works best on a slab with a localized low spot and little cracking, not on a badly broken slab 1.
- The grout is heavy and fills voids mostly near each hole, so patterns and lift limits matter 21.
- It does not fix the cause of the settlement. If water or poor fill is still at work, the slab can sink again 1.
- It is a slab fix, not foundation underpinning. A slab that is part of the structure should be checked by an engineer first.
What mudjacking is and why slabs sink
General information, not a diagnosis of your house. The Federal Highway Administration (FHWA) defines slab jacking as pressure insertion of a cement-grout mixture or polyurethane material beneath a slab to slowly raise it until it reaches a smooth profile 1. The traditional version, with a cement-based slurry, is what most people mean by mudjacking.
Slabs sink when the soil or base under them loses support. FHWA ties settlement to poor foundation support, most often in fill areas, over culverts and at bridge approaches 1.
An Oregon Department of Transportation (ODOT) study traced one settling slab to a leaking drainpipe: water suspended soil particles, traffic pumped them out, and a void formed 2.
The same logic applies to a driveway, walkway, patio or garage slab. Water, erosion and loose fill create voids. Mudjacking refills them and lifts the slab. For the foam alternative, read polyurethane foam slab lifting. For support under footings, see foundation underpinning.
Two cutaways of a sunken concrete slab. Left: drilled holes fed with a cement slurry fill voids and lift the slab. Right: smaller holes injected with expanding foam that fills voids and lifts the slab.
Illustrative drawing, not to scale and not a design. It shows grout or foam injected through holes to fill a void and raise a slab. Hole count, pattern and lift amounts are decided by the installer and, for structural slabs, an engineer.
Lifting a slab is not stabilizing a foundation
Mudjacking raises and fills a slab. It does not carry a footing down to firm soil, and it does not make a foundation resist further movement. If a house’s foundation is moving, an engineer decides what to do about it before anyone raises a slab.
How mudjacking works, step by step
FHWA and ODOT describe the process for pavements. A driveway or patio uses the same logic at smaller scale.
- Profile the slab. The low areas are measured so the lift target is known 1.
- Drill injection holes. Holes are drilled through the concrete to the base soil. ODOT describes conventional grout holes of about 2 to 3 inches 2. Drilling should avoid breaking out the underside of the slab 1.
- Pump the grout. A pump pushes a cement-based mix beneath the slab. The amount of lift is controlled by injection pressure 2.
- Lift in small steps. FHWA says pumping often starts at the middle of the depressed slab and works outward, and that a slab should be raised no more than 0.25 inch at a time at each hole to avoid stress that causes cracking 1.
- Check as it rises. A stringline or laser level shows progress 12.
- Seal the holes. Municipal specifications call for patching the holes flush with the surface 3.
Slabs can crack if lifted too fast or too far
FHWA names excessive lifting as the main concern, because it induces stress that can crack the slab 1. Do not try to jack a slab yourself, and do not lift a slab that is attached to or supporting part of a house without an engineer’s input.
Slab treatments that get confused with each other
| Treatment | Goal | Typical materials | Notes |
|---|---|---|---|
| Slab jacking (mudjacking) | Physically lift a depressed slab back to the level of its neighbors 1 | Cement grout or polyurethane 1 | Stiffer mixes than for stabilization 1 |
| Slab stabilization (undersealing) | Fill voids to restore support without lifting 1 | Cement grout, polyurethane, sometimes asphalt 1 | Done where loss of support is known 1 |
| Polyurethane foam lifting | Lift or stabilize with expanding foam 1 | Two-part polyurethane 2 | Covered on its own page |
| Underpinning with piers | Support a footing from deeper soil 4 | Steel or concrete piers | A different problem and fix |
Example: what a public specification asks of a slab jacking job
The specification example below reads a city specification for sidewalks, curbs and slabs, and FHWA guidance. It shows the kinds of checks a good scope contains. It is not a standard for your home 31.
| Item | What the specification asks | Why it matters to a homeowner |
|---|---|---|
| Before work | The site and the existing condition of the slab are inspected, noted and documented 3 | Gives you a record of cracks that were there already |
| Hole size | Holes drilled vertically, with a stated maximum diameter 3 | Smaller holes mean smaller patches |
| Lift target | Raise to within a small tolerance of the target elevation 3 | The scope should state the finished elevation |
| Cold weather | No jacking when the air is at or below 5 degrees Celsius without written approval 3 | Ask what cold-weather limits your contractor works to |
| Finish | Grout holes sealed flush and the site cleaned up 3 | Ask who patches and what the patch looks like |
| Damage | Slabs damaged by excessive force are replaced by the contractor 3 | Ask how breakage is handled in your contract |
- SurveyFind low areas
- DrillHoles through the slab
- PumpGrout beneath the slab
- LevelSmall lifts, checked
- SealPatch the holes
A general order drawn from FHWA and ODOT descriptions, not a schedule for any slab. Source: [1] [2] [3]
A residential contract will differ, but these are fair questions to ask. See the slab leveling service page.
Where mudjacking is used, and where it is not
FHWA describes ideal slab jacking projects as pavements with localized settlement that are generally free of cracking, such as settlement over fill, culverts and bridge approaches 1. By analogy, the sources point to driveways, sidewalks, patios and garage slabs with a low spot.
It is not recommended for repairing faulted joints along a pavement, which FHWA says are better addressed by other treatments 1.
For a house, the question is whether the slab is part of the structure. A slab-on-grade that carries walls, or a slab tied to footings, is not just a floor. An engineer decides. See foundation types and slab-on-grade foundation.
If the slab sank because the footing under the wall settled, lifting the slab alone leaves the cause in place. A foundation settlement evaluation comes first.
What mudjacking does well and what it costs you
What it can do
Trade-offs
- Conventional grout holes are larger than foam holes, and the grout generally fills voids only near the hole 2.
- The material is heavier than foam, so it adds more weight to weak soil 12.
- Raising too fast or too far can crack the slab 1.
- It does not fix the cause. Water or poor fill can bring the settlement back 1.
- The amount of grout depends on how large the voids are, which may not be known until work starts, so ask whether a quote is fixed or by volume.
What mudjacking cannot promise
FHWA warns that slab jacking by itself may not be enough if the underlying mechanism, such as excess moisture, poor load transfer or poor consolidation, is not addressed. The same distress can return 1. For a driveway, that can mean a downspout, a leaking pipe or an eroding base.
Mudjacking also cannot fix a broken slab. It lifts a slab that is mostly intact. Cracked, tilted or heaved slabs may need replacement.
It cannot support a footing. If a house is settling, mudjacking a floor slab does not stop the foundation from moving.
The Foundation Performance Association notes that after lifting a foundation, a void under a slab should often remain, to limit the effects of swelling soil lifting the foundation, so filling it is a decision for an engineer, not a default 4.
What drives the price of mudjacking
We do not give prices. A fair figure needs dated local quotes for a defined scope. The drivers are the slab area and thickness, how far it must be raised, how big the voids are, the number of holes, site access and weather.
Grout volume depends on void size, which may not be known until work starts, so ask whether the quote is fixed or by volume. Patching, cleanup, repairs to damaged concrete and any drainage fix add cost.
Compare mudjacking with replacement, and with foam, on a like-for-like scope. See the cost guide and the cost calculator for how quotes are built.
How to approach a slab lifting project
- Photograph and date the slab, cracks and any gaps at doors or walls. Use the crack identification tool to describe what you see.
- Find the water. Check downspouts, grading and plumbing near the slab.
- Ask whether the slab is structural. If it ties to walls or footings, involve an engineer. See the engineer guide.
- Get written scopes that state the target elevation, hole size, patch method and warranty.
- Ask who pays if the slab cracks during lifting.
- Watch for new settlement after the first wet season and record it.
Keeping a lifted slab from sinking again
- Direct roof water away from the slab. Extend downspouts and clear gutters.
- Keep soil sloping away from the building. Backfill settles over time, and Kansas State extension advises adding fill to keep a slope of at least 6 inches in 10 feet 5.
- Fix any leaking pipe or irrigation line near the slab quickly.
- Seal joints and cracks so water does not wash soil out.
- Photograph the slab each season and compare levels with a straightedge.
- Keep the contractor’s scope and warranty. See warranties.
Risks and signs to take seriously
- Cracking from lifting too fast or unevenly 1.
- Hidden voids that take more grout than planned.
- Extra weight on soft soil, since cement grout is heavier than foam 12.
- Water lines or conduits under the slab hit during drilling.
- Settlement that returns because the cause was never fixed 1.
Call a licensed structural engineer when
Cracks run through walls as well as the slab, doors and windows stick together with new cracks, floors slope toward a wall that is moving, or the slab ties into a foundation you worry about. Do not drill, pump or jack anything beside a foundation yourself.
Specifications, permits and who regulates the work
We found no residential code section that specifies mudjacking. The documents we loaded are public-works guidance: FHWA’s pavement preservation guide, an ODOT research report and a city standard construction specification for sidewalks, curbs and slabs 123. They describe good practice. They are not rules for your home.
Contractor licensing and permits for residential concrete work differ by state and city. Verify a contractor’s license with the state or local board, and ask your building department whether a permit applies. A slab that is part of the structure may need engineering review under local rules.
See how we vet for what we check and do not check.
Mudjacking next to foam lifting and replacement
| Feature | Mudjacking (cement grout) | Polyurethane foam |
|---|---|---|
| Material | Cement-based grout 1 | Two-part polyurethane that expands 2 |
| Injection hole size | About 2 to 3 inches in ODOT’s description of conventional grout 2 | About 5/8 inch in the polyurethane method ODOT studied 2 |
| Weight on the soil | Heavier 1 | Lightweight, so it adds little settlement load 1 |
| Time to use | Ask the contractor how long before the slab can take load | Traffic can open in as little as 15 to 30 minutes in highway use 1 |
| Void filling | Mostly near each hole 2 | Expands to fill surrounding voids 1 |
| Evidence | Long highway use with defined mixes 1 | Good results in several states, mixed in others 1 |
Mudjacking myths
- Myth Mudjacking permanently fixes a sinking slab.
- Reality It fixes the lift, not the cause. If water or poor fill remains, settlement can return 1.
- Myth Any sunken concrete can be mudjacked.
- Reality FHWA’s ideal case is localized settlement in a slab free of cracking 1.
- Myth Mudjacking and foundation repair are the same.
- Reality One lifts a slab. The other supports a footing. See the underpinning page.
- Myth The bigger the lift in one pass, the better.
- Reality FHWA says no more than a quarter inch at a time at each hole 1.
- Myth It always costs less than replacing the slab.
- Reality Price depends on scope; we publish no prices and no source supports a blanket claim.
Where soil and climate change the job
Settlement is most often tied to fill, culverts and wet or poorly drained ground 1.
Cold weather matters: one city’s specification bars slab jacking when the air is at or below 5 degrees Celsius without written approval 3.
In expansive clay regions, a slab can rise as well as sink with moisture, and lifting a slab that is simply heaving is the wrong tool.
Deciding whether mudjacking fits your slab
Mudjacking fits a mostly intact slab with a localized low spot, where the cause can be found and treated. It fits poorly where the slab is broken, where the foundation is moving or where the slab is heaving.
The guide below turns that into questions. For the wider options, see repair methods and foundation repair.
- If One low spot in an otherwise sound slab
- Then Ask about lifting and about the cause of the void 1
- If The slab is cracked in many places
- Then Ask whether replacement is more sensible than lifting
- If A wall or footing nearby is moving
- Then Ask an engineer about the foundation before any slab work
- If The slab is rising, not sinking
- Then Ask about heave and moisture, not lifting 4
Slab or foundation first?
If walls, doors or foundation cracks are involved, start with an engineer, not a slab contractor. Our engineer or contractor tool helps you decide whom to call.
Questions about Mudjacking
What is mudjacking?
Mudjacking, also called slabjacking, is a repair that raises a sunken concrete slab by pumping a cement-based slurry through drilled holes beneath it. The slurry fills voids and pushes the slab up. Federal Highway Administration guidance describes it as pressure insertion of a grout mixture beneath a slab to raise it to a smooth profile.
How does mudjacking work?
Holes are drilled through the slab, a pump injects grout beneath it, and the slab rises as the grout spreads and pushes against it. Crews pump in small steps and check the level as it rises. FHWA advises no more than a quarter inch of lift at a time at each hole to avoid cracking.
What is the difference between mudjacking and slabjacking?
They usually mean the same thing. Slabjacking is the formal name for raising a slab by injecting material beneath it. Mudjacking is the common name for the cement-slurry version. Some contractors use the words for foam work as well, so ask which material is being used.
Can mudjacking fix a sinking foundation?
No. Mudjacking lifts and fills slabs. It does not put support under a footing or stop a foundation from moving. If walls, doors or footings show movement, an engineer should evaluate the foundation first. Foundation underpinning is a different repair for a different problem.
How long does mudjacking last?
It depends on why the slab sank. FHWA warns that if the cause, such as moisture or poor consolidation, is not addressed, the same distress can return. We found no reliable lifespan figure. Fix water sources first, and ask the contractor what their warranty covers.
Is mudjacking better than polyurethane foam?
Neither is better in general. Grout is heavier and uses larger holes. Foam is lightweight and uses smaller holes. Highway agencies report good results with foam in several states and mixed results in others. Compare scope, warranty and site conditions rather than choosing by material alone.
Can a slab crack during mudjacking?
Yes. FHWA says the main concern is raising the slab too much or too fast, which induces stress that can cause cracking. That is why lift is done in small increments and monitored. Ask how the contractor handles a slab that cracks, and get it in writing.
Do I need a permit or an engineer for mudjacking?
Rules vary by city and state, and we found no residential code that names mudjacking. If the slab ties into the house structure or walls are moving, involve an engineer. Ask your building department about permits and verify the contractor’s license with the issuing board.
How much does mudjacking cost?
We do not publish prices. The drivers are slab area and thickness, lift height, void size, hole count, access, weather and patching. Grout volume depends on void size, so ask whether the quote is fixed or by volume. Our cost guide and calculator show how quotes are built.
Sources
- Federal Highway Administration, Concrete Pavement Preservation Guide, 2nd ed., FHWA-HIF-14-014 (September 2014), Chapter 4: Slab Stabilization and Slab Jacking, retrieved .
- Oregon Department of Transportation, Injected Polyurethane Slab Jacking, FHWA-OR-RD-02-19 (June 2002), retrieved .
- City of Regina, Saskatchewan, Standard Construction Specification, Section 2780: Slab Jacking (revised April 2017), retrieved .
- Foundation Performance Association, FPA-SC-08-1: Design, Manufacture, and Installation Guidelines of Precast Concrete Segmented Piles for Foundation Underpinning (2014), design considerations, retrieved .
- Kansas State University Research and Extension, Dry Basements and Crawl Spaces, MF2809 (April 2008), retrieved .
Expert review
Written by the HyreFoundation Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: How slab jacking works, limits and material descriptions come from the Federal Highway Administration’s concrete pavement guide, an Oregon DOT research report, and a City of Regina standard specification.
All three concern pavements, sidewalks and public slabs, not houses, and are used for general mechanics and good-practice questions. The void note comes from a Foundation Performance Association guideline.
No residential code section naming mudjacking was found. No prices are given. No contractor or company is named. Rules checked 2026-10-14. General information, not engineering advice.
Suggest a correction. We fix errors and say what changed.