Mudjacking and polyjacking both lift a sunken slab by pumping material into the gap under it. Mudjacking uses a cement grout through holes about 2 to 3 inches wide; polyjacking uses a two-part foam that expands, through holes about 5/8 inch wide, and weighs much less. Either one only works on a slab that's still in one piece, and only if whatever washed out or compressed the soil underneath gets fixed first.
Before you start
Lifting fixes the height of a slab, not why it dropped. Check these before you call for quotes.
- Where the downspouts and any sump discharge empty
- Whether the ground slopes toward the house or the slab
- Whether the slab is in one piece or broken into chunks
- Whether the foundation wall next to it has new cracks
If any of these fit, find out who to call first: a structural engineer or a repair contractor.
What is the difference between mudjacking and polyjacking?
The material and the hole size. Mudjacking pumps a cement-based grout (the “mud”) under the slab through holes a few inches wide, while polyjacking injects a two-part polyurethane that foams and expands under the slab, through much smaller holes.
The Oregon Department of Transportation tested polyjacking on highway slabs in a study of slab jacking (opens in a new tab) and described how it differs from conventional grout jacking. Its findings are the clearest public numbers on the two methods, and most of the table below comes from that report.
| Mudjacking (grout) | Polyjacking (foam) | |
|---|---|---|
| What goes under the slab | Cement-based grout, pumped in | Two-part polyurethane that expands to several times its liquid volume |
| Hole size | About 2 to 3 inches | About 5/8 inch (16 mm) |
| Weight added under the slab | Heavier than foam (the report gives no figure) | Light: the foam maker listed 5 to 20 lb per cubic foot |
| How the lift is controlled | Pump pressure | Injection rate, in several small lifts if needed |
| How far it reaches | Generally fills gaps only near the hole | Spread into openings as narrow as 1/4 inch in testing |
| Back in use | Ask the contractor for the grout's cure time | Maker claim: 90% of strength within 15 minutes |
| What neither fixes | A slab broken into pieces, a scaled surface, or the water and soil problem that sank it | Same |
Oregon Department of Transportation, Injected Polyurethane Slab Jacking (2000)
Which is better, mudjacking or polyjacking?
Polyjacking uses smaller holes and lighter material, and its maker claims faster use. Mudjacking is the older method and still lifts a slab, so how well the crew finds and fixes the cause matters as much as the method.
The weight matters most on soft soil. The Oregon report notes that the foam’s low density, compared with grout or mud, should cause less settling (opens in a new tab) from the material’s own weight, and that it spread into gaps as narrow as 1/4 inch and some as narrow as 1/8 inch.
Foam’s speed is the other draw. The foam maker’s claim in the same report is 90% of full strength within 15 minutes, the point at which it says traffic can resume.
Prices for both vary by region, slab size and how much material it takes, so get written quotes for the method you’re considering rather than relying on national averages.
Why do concrete slabs sink?
Because the soil under them washed out or compressed. A slab can’t settle unless something under it moved, so finding that cause decides whether a lift holds.
- Water washing soil out. In the Oregon trial, water probably carried soil out from under the slabs and left a void; the source was a leaking 12 inch drainpipe, which was repaired before the slabs were lifted.
- Loose fill that settles. InterNACHI notes that soil that wasn’t compacted well (opens in a new tab) settles as the weight above presses it together, and not always evenly. The University of Illinois Extension calls poor backfill and compaction around foundation walls the main reason ground settles near a house (opens in a new tab).
- Downspouts and bad grading. InterNACHI describes a foundation undermined by decades of downspout water, and ground sloping toward a house soaks the soil next to it. The Illinois Extension recommends that the final grade slope at least 4% away from the house.
- Tree roots. InterNACHI notes that roots can heave concrete, which leaves one slab higher than the next instead of lower.
A sinking driveway at the garage door, or a porch or patio slab dropping along the house, often sits on that backfill: soil dug out to build the foundation, then put back. The Illinois Extension says backfill should go in layers, compacted under a geotechnical engineer’s direction.
When is an uneven sidewalk a trip hazard?
When one slab sits more than 1/4 inch above the next. The federal ADA accessibility standards allow a change in level of up to 1/4 inch (opens in a new tab) to be vertical, require anything from 1/4 to 1/2 inch to be beveled, and call for a ramp above 1/2 inch.
That’s a standard for accessible public routes, but it’s a useful yardstick at home. InterNACHI says inspectors should treat vertical displacement (opens in a new tab) between slabs as a trip hazard and recommend correction.
An uneven sidewalk can be ground down, lifted or replaced. InterNACHI gives an example where grinding off the raised edge cost less than tearing out and replacing the slab; lifting suits a sunken slab, and the sidewalk crack guide covers the city rules that often apply to public walks.
When should you replace a sunken slab instead of lifting it?
When the slab is broken into pieces, crumbling or badly scaled. Lifting raises the slab you have, so it only makes sense if that slab is worth keeping.
- Broken into several pieces. Each piece moves on its own, and the cracks between them keep letting water in.
- Surface flaking or spalling over much of the slab. The spalling and scaling guide explains when surface damage is past repair.
- Rusted steel showing in the cracks or broken edges.
- A cause that can’t be fixed, such as a slab over ground that keeps washing out.
The repair or replace guide walks through the full decision, including what a replacement quote should list.
What if the slab is sinking next to the foundation?
Check the foundation wall before you lift anything. A patio, stoop or driveway sinking along the house usually sits on the backfill around the foundation, and water that soaks that soil reaches the wall too.
Have a structural engineer look before any lifting if the wall next to the sunken slab shows horizontal basement wall cracks, bowing walls, wall cracks wider than 1/4 inch, offset edges or stair-step cracks in block walls. Those point to a wall problem, and the wall gets fixed first.
If the wall shows only thin vertical cracks, the foundation crack guide covers how to judge them. Lifting the slab can wait until you know.
What should a slab lifting quote include?
The cause, the method, how many holes and how they’ll be sealed, and what happens if the slab settles again. The American Concrete Institute says the cause of the damage must be assessed and corrected (opens in a new tab) for a repair to last, so a quote that skips the cause is incomplete.
- What caused the settling, and what you or they will fix first: downspouts, grading, a leaking pipe.
- Method and material: grout or foam, and the foam’s density if foam.
- Number and size of holes, and what they’ll be filled with. The Oregon crew sealed foam holes with a cement grout, and many of those seals were gone four days later, so ask how they’ll be checked.
- How the lift is checked. The Oregon crew watched elevations with a string line or laser level while injecting.
- Target height for each slab, especially where it meets the garage, steps or house.
- Warranty: how long, what counts as settling, and whether a re-lift is included.
The Federal Trade Commission says a written home improvement estimate (opens in a new tab) should describe the work, the materials, the completion date and the price, and advises against automatically choosing the lowest bidder. Get more than one quote, and compare what each includes, not just the total.
Questions
Can I lift a sunken concrete slab myself?
It's a contractor job. Both methods need pumping equipment, and the Oregon Department of Transportation's report describes two workers injecting to cut the risk of cracking, with a string line or laser level to watch the slab's height. What you can do yourself is fix the cause: downspouts, grading and leaking pipes.
How long does polyjacking last?
The best public data is short term. In the Oregon Department of Transportation's study, foam-lifted highway slabs had settled up to 0.413 inch (opens in a new tab) two years later, and the foam had not lost strength underground. How long a lift lasts at your house depends mostly on whether the water or soil problem that sank the slab was fixed.
Will the cracks close when the slab is lifted?
Lifting brings the edges back level, but it won't glue a crack shut. Once the slab is up and has stopped moving, fill the remaining cracks like any other crack in a flat slab.
Does homeowners insurance cover a sinking driveway?
Policies differ, and settling is often treated differently from sudden damage such as a burst pipe. Read your policy and ask your agent before you pay for work you plan to claim.
What is concrete leveling?
Concrete leveling is the general name for lifting a sunken slab back to level by filling the gap underneath it. Mudjacking, slabjacking and polyjacking are all forms of concrete leveling.