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Polyjacking
A contractor has quoted foam injection and you want to know whether that is the right method here.
Polyjacking lifts settled concrete by injecting expanding polyurethane foam through small holes drilled in the slab. The two components mix at the injection point, expand rapidly, fill the void beneath the concrete, and raise the slab as they do.
It is the newer of the two mainstream lifting methods and has become the default in much of the residential market. That popularity is largely deserved, but it is not automatically the right choice for every job, and "we use foam" is a description of a contractor's equipment rather than an argument about your concrete.
Why the weight matters
The most substantive argument for foam is density. Cured polyurethane lifting foam is a fraction of the weight of a cementitious slurry filling the same space. When a slab settled because the ground beneath it could not carry what was on it, adding a large mass of heavy material to that same ground is at least worth thinking about.
How much this matters in practice depends on the soil. On ground that settled from erosion or a consolidating trench backfill, it may matter very little. On soft or poorly compacted fill, it can matter a good deal. A contractor who can explain which situation you are in is more useful than one who only explains that foam is lighter.
Holes, cure time and disruption
Foam injection uses holes roughly the diameter of a pencil, compared with holes around the size of a quarter or larger for slurry. Fewer and smaller holes means less visible patching, which matters more on a front walkway or a patio than on a garage floor.
Cure time is the other practical difference. Foam reaches most of its strength within minutes, so the area typically returns to use the same day. That is a genuine convenience on a driveway that a household depends on.
Where foam's advantages are oversold
Foam is sometimes marketed as permanent, or as waterproof, or as though it stabilises soil. It fills a void and it resists water itself, but it does not consolidate the surrounding ground, and it does not stop water from continuing to move soil somewhere else under the same slab.
It also does not make a slab stronger. A cracked slab lifted on foam is a cracked slab at a new height. Any claim that a lifting method addresses the condition of the concrete rather than its elevation should be treated sceptically.
When foam is the sensible pick
- Appearance matters and smaller patched holes are worth paying for.
- The slab needs to be back in service quickly.
- The ground beneath is soft or was poorly compacted, so adding weight is a real concern.
- Access is tight — foam rigs generally need less room than slurry pumping setups.
- The lift required is precise, such as matching a garage floor to a threshold.
When foam is not obviously better
- A large void under a big area, where material volume dominates the price and slurry may cost considerably less.
- Any job where the concrete itself is the problem — foam does not help concrete that is failing.
- Situations where the underlying cause is untreated water movement; the method does not change that outcome.
Alternatives worth pricing
- Mudjacking, where volume is large and cost per cubic foot is the deciding factor.
- Replacement, where the slab is not worth lifting.
What moves the price
We do not publish national dollar figures. A single average applied across every site, method and market gives you a confident-looking benchmark that is wrong for your job in an unknown direction. What does transfer between jobs is the structure of the price:
- Volume of foam required, which tracks the size of the void rather than the slab's footprint.
- Number of injection points and drilling time.
- Access and setup.
- Minimum job charges, which many contractors apply and which can dominate a small job's price.
Local quotes decide actual pricing. If you want to compare two of them properly, the quote comparison guide covers how.
What to ask a contractor
- Why foam rather than slurry for this specific slab?
- How many injection points, and where will they be?
- What is your plan if the slab does not lift evenly?
- When can I use the area again, in writing?
- What does the warranty exclude?
Common questions
Is polyjacking better than mudjacking?
It is better at some things — weight, hole size, cure time — and not inherently better overall. On a large void where material volume drives the cost, slurry can be substantially cheaper for a comparable result. The right question is which suits your slab and your ground, not which method is newer.
Does the foam break down over time?
Closed-cell polyurethane lifting foams are formulated to resist water and stay dimensionally stable once cured. The realistic failure mode is not the foam degrading; it is the surrounding soil moving again, which no filling material prevents.
Can foam lift a slab that has already cracked?
It can raise it, but the cracks come up with it, and lifting can open them further or create new ones. Whether that is acceptable depends on how much cracking there is and what the slab is for. This is worth a frank conversation before work starts, including who bears the cost if it breaks.
Work it out, or judge the quote
Related guides
Concrete leveling
Raising settled slabs back toward their original height instead of tearing them out.
Read more →Mudjacking (slabjacking)
Cementitious slurry lifting: long-established, cost-effective on volume, heavier, with larger patched holes.
Read more →Polyjacking vs mudjacking
Foam or slurry: the differences that matter and the ones that are marketing.
Read more →Voids under concrete
Space beneath a slab — often before anything has visibly dropped.
Read more →What drives leveling cost
Why lifting is priced by the void rather than by the slab, and what makes two quotes differ.
Read more →