Costs and decisions
Polyjacking vs mudjacking
Two contractors have proposed two different lifting methods and both say theirs is better.
Both methods raise a settled slab by filling the space underneath it. They differ in what they fill it with, and those differences are real but narrower than the marketing on either side suggests.
Neither is universally better. The right question is which suits your slab, your ground and your priorities. Where the two are priced differently for the same slab, the reason is usually one of the standard lifting cost factors rather than the material itself.
The differences that are real
Weight. Cured polyurethane foam is far lighter than a cementitious slurry filling the same space. On ground that has already demonstrated it struggles to support load, that is a legitimate technical argument for foam.
Hole size. Foam uses holes roughly pencil-diameter; slurry needs holes around quarter-size or larger. Both are patched; foam's are less noticeable. On a front walkway this matters; on a garage apron it usually does not.
Cure time. Foam reaches working strength in minutes; slurry needs longer. On a driveway a household depends on daily, that is a practical difference.
Cost structure. Slurry material is inexpensive; polyurethane is not. On jobs where a large volume is needed, slurry can be considerably cheaper for the same finished elevation.
The differences that are oversold
"Foam is permanent." No lifting method is permanent, because none of them stop the ground from moving again. Foam is durable and water-resistant once cured; that is not the same claim.
"Foam stabilises the soil." It fills a void. It does not consolidate the surrounding ground or stop water moving material elsewhere under the same slab.
"Mudjacking is obsolete." It is older and has lost share, but it works, and on volume-heavy jobs it can be the better value.
Either method described as fixing cracks or strengthening concrete. Neither does. Both address elevation only.
Choosing between them
Lean foam where the ground is soft or poorly compacted, where appearance matters, where the area must return to service quickly, or where access is tight.
Lean slurry where the void is large and material volume dominates the price, where the location is utilitarian, and where the ground is competent enough that added weight is not the deciding concern.
Where a contractor offers only one method, ask what would make them recommend the other. If the answer is that there is no such situation, that is worth noting.
Questions that separate a considered recommendation from a default
Both methods have genuine advocates, and a contractor recommending the one they own equipment for is not being dishonest. What distinguishes a considered recommendation is whether it refers to your ground rather than to the method in general.
Ask what they found when they probed or sounded the slab, how large they think the space beneath it is, and how that informed the choice. Ask what they would use if the space turned out to be twice the size they estimated, and whether that changes the price or the method.
A contractor who can answer those has assessed a site. One who answers with the general advantages of their method has assessed nothing, and the recommendation is really a description of their van.
What to ask a contractor
- Why this method for this specific slab and this specific ground?
- What would make you recommend the other method here?
- How much material do you expect to use, and what happens if it takes more?
- How long before I can use the area, in writing?
- What does the warranty exclude?
How we know what this page says
Each of these is something this page says. What follows is why we say it, what we had to assume, and what would change our mind — so you can weigh it rather than take it on trust. How we grade what we publish.
Neither polyurethane foam nor cementitious slurry lifting is the better method in general.
Mixed evidence Competent, honest people reach different conclusions here, and the disagreement is real rather than a matter of one side being out of date. Both positions have support and both have failure cases.
Evidence considered
- The two methods differ in material weight, injection hole size, working time and how the material behaves in wet ground.
- Each has situations where its properties are an advantage and situations where they are a disadvantage.
- Experienced practitioners disagree, and the disagreement does not track experience or competence.
Still to establish
- Void depth and extent
- Subgrade and compaction
- Use and loading — you can check this yourself
- Water source — partly, on your own
- Access — you can check this yourself
Why we say this, and when it may not apply
Both are marketed as the modern correct answer, usually by whoever owns the equipment. The genuine differences are real but they are trade-offs rather than a ranking, and homeowners are entitled to know that the disagreement is honest.
What we had to assume
- That both methods are available in the area and competently executed, which is not everywhere true.
- That the choice is being made on suitability rather than on which equipment is already on the van.
When this may not apply
- Where only one method is realistically available locally, the comparison is academic.
- Where access limits equipment, the decision may be made by the site rather than by the merits.
- Where the ground is saturated, the material properties matter more and the trade-off shifts.
What would change it
- Establishing how much load the surface actually carries, which changes how much the material weight difference matters.
- Establishing the moisture condition of the ground beneath.
- Establishing the depth and extent of the void, which affects material volume and behaviour.
Mixed evidence does not mean this: It does not mean the choice does not matter, and it does not mean you should pick whichever is cheaper. It means the deciding factor is usually something specific to your property rather than a general rule.
Common questions
Which lasts longer?
Both last as long as the ground under them stays put, which is a property of the site rather than of the material. Where the cause of settlement is unaddressed, both fail on a similar timescale. Where it is addressed, both can hold for years.
Is foam worth the extra cost?
On soft ground, on visible flatwork, or where you need the area back immediately — often yes. On a large void under a utilitarian slab on competent ground, the extra may be buying you very little. It depends on which of foam's advantages you actually need.
Work it out, or judge the quote
Related guides
Polyjacking (foam injection)
Polyurethane foam injection: light, fast-curing, small holes — and more expensive per unit of material.
Read more →Mudjacking (slabjacking)
Cementitious slurry lifting: long-established, cost-effective on volume, heavier, with larger patched holes.
Read more →Concrete leveling
Raising settled slabs back toward their original height instead of tearing them out.
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 →Leveling vs replacement
When lifting is the smart economy and when it is a deposit on a job you will still do.
Read more →