Slabjacking, Mudjacking and Polyurethane Foam: How They Work and Their Limits
Slabjacking raises a settled concrete slab by injecting material beneath it. It is a legitimate, widely used repair for driveways, walks, garage and patio slabs, but it treats the symptom of lost support, not the soil or water problem that caused it.
What it is
The American Concrete Institute (ACI) defines slabjacking as raising a slab-on-ground to a target elevation, filling voids beneath it, or both, by injecting material under pressure.[1] ACI's Repair Application Procedure 11 (copyright 2010, committee E706) is the main neutral reference we found.
The two material families
| Material | Description | Trade-offs noted |
|---|---|---|
| Cementitious grout ("mudjacking") | Mortar-type mixes, often with fly ash for pumpability. Holes are typically 1-1/2 to 2-1/2 inches in diameter.[1] | Mixes vary with applicator experience and void depth; larger holes remain visible; the added weight of grout may cause further settlement. |
| Polymer foam (often polyurethane) | Two-component foams that mix during injection and expand. Holes are 1/2 to 3/4 inch.[1] | Quick and cleaner, but ACI notes the cavity often is not fully filled because the reaction is rapid. |
(ACI uses the term polymer foams rather than naming polyurethane.[1])
When it is appropriate
ACI says slabjacking suits slabs that have settled or lost support from poor compaction, soil shrinkage or sub-base erosion, and that soil conditions should be evaluated first because slabjacking does not fix them. It calls it a cost-effective alternative to replacement with little landscape disruption and minimal downtime, and says it can be done in most weather.[1]
Limits and cautions
- "Slabjacking will level the slab, but it won't correct any underlying poor soil conditions."[1]
- If settlement continues, repeat treatment may be needed, and a slab may keep sinking if the soil has not stabilized.[1]
- Lift in increments no greater than 1/4 inch at one hole at a time to avoid cracking.[1]
- Grout follows the path of least resistance, so sewers, utilities and drains can fill unintentionally; pumping pressures should be monitored.[1]
- Hot conditions increase binding and cracking risk.[1]
- If distress is severe, slab replacement should be considered.[1]
What this means for a house foundation
ACI's bulletin is about slabs on ground. For house foundations, the ASCE Texas Section guidelines list grouting or mudjacking among slab foundation remedies but caution that grouting should not be placed beneath underpinned areas if soil swelling could damage the structure.[2] Lifting a house slab can also stress plumbing and gas lines, so the guidelines advise testing them afterward.[2] Use of foam or grout under the structural slab of a house is a decision to take to an engineer.
Questions to ask
- What caused the settlement, and has that been addressed (drainage, leak, compaction)?
- Which material will be used and why? How will you monitor lift and pressure?
- How will you protect or check sewer lines and utilities under the slab?
- What if the slab settles again? What does the warranty say?
Common questions
What is the difference between mudjacking and polyurethane foam?
Mudjacking uses a cementitious grout injected through larger holes; foam is a two-component polymer injected through smaller holes. ACI notes foam work is quicker and cleaner but may not fully fill the cavity.[1]
How long does slabjacking last?
It lasts as long as the soil stays stable. ACI says it does not correct poor soil conditions and that continued settlement may need repeat treatment.[1]
Can slabjacking damage pipes?
It can if not controlled. ACI warns grout follows the path of least resistance and may fill sewers, utilities and drains unintentionally.[1]
Related guides
Sources
Figures and claims marked with a number come from these sources. Dates are the publication or last-update dates shown by the publisher, where one was shown. Older sources are flagged in the text.
- RAP Bulletin 11: Slabjacking (ACI RAP-11). American Concrete Institute, Committee E706; primary author Fred R. Goodwin; copyright 2010.Covers slabs on ground (floors, pavements), not house foundations as a whole.
- Guidelines for the Evaluation and Repair of Residential Foundations, Version 1. Texas Section, American Society of Civil Engineers; adopted October 3, 2002, effective January 1, 2003.Written for Texas conditions and by its own terms not a standard of care. Widely used as a reference for slab and pier-and-beam evaluation. Published in 2002.