Two increasingly common foundation repair options are polyurethane foam lifting (also called resin injection or slab lifting) and traditional underpinning. Both can lift and stabilise a settled foundation, but they work very differently, suit different problems, and have different cost profiles and longevity. In Wagga Wagga’s reactive clay environment, choosing the right method for the right application is critical. For a deep dive into resin injection specifically, see our resin injection underpinning guide.
Quick answer (BLUF)
Polyurethane foam lifting is fast (typically 1 day), less expensive, and suits minor slab settlement in reasonably stable soils. Traditional underpinning (mass concrete or screw piers) is more permanent, more appropriate for significant movement and reactive clay sites, and is the standard recommendation for structural foundation failure. For most Wagga Wagga homes with active foundation problems, traditional underpinning is the more robust long-term solution.
How polyurethane foam lifting works
Polyurethane foam lifting (also marketed as “uretek,” “mudjacking,” or “slab lifting”) involves drilling a series of small holes (typically 12-16 mm diameter) through a concrete slab or adjacent to a footing, then injecting a two-component expanding polyurethane resin. The resin expands as it cures, compressing loose soil, filling voids, and exerting upward pressure that can lift the slab.
The injection is highly controllable, the operator monitors level in real time using precision instruments and stops injecting when the target level is reached. The holes are then filled with a matched concrete patching compound.
Advantages:
- Fast: most jobs completed in one day
- Minimally invasive: no excavation, small patch holes
- No wait time for concrete to cure
- Less expensive than full underpinning for the same area
- Occupants can usually remain in the home throughout
Limitations:
- Does not address the underlying cause of settlement
- Not designed for deep or highly reactive subsoils
- Less effective where the reactive zone extends below the resin injection depth
- Foam can degrade over time, particularly where soil moisture cycles are extreme (as in Wagga’s climate)
- Not suitable for heave situations, only for settlement
- Limited ability to carry the structural loads required for significant underpinning
How traditional underpinning works
Traditional underpinning extends the foundation to a deeper, more stable level. The main methods are:
Mass concrete underpinning: Pits are excavated beneath the existing footing in a sequential pattern, then filled with concrete. The new concrete bears on stable subsoil or rock below the reactive zone, providing permanent structural support independent of the reactive clay above.
Screw (helical) pier underpinning: Steel piers with helical flights are rotated into the ground using hydraulic equipment, bypassing the reactive zone and developing bearing in stable material. Load-transfer brackets are then attached to the existing footing and the structure is jacked to level.
Concrete pier underpinning: Bored concrete piers extending to rock or stable layer, with load transfer through brackets or grade beams.
Advantages:
- Permanent structural solution
- Independent of reactive clay behaviour after installation
- Industry-standard for significant foundation movement
- Eligible for engineering certification and warranty
- Does not rely on soil compaction (important where the reactive zone is deep)
Limitations:
- More expensive
- Longer installation time
- More disruptive (excavation, concrete work)
- Requires council or engineering oversight in some cases
Which is right for Wagga Wagga?
The choice depends on the nature and severity of the problem:
When polyurethane foam lifting is appropriate
- Minor settlement (under 20 mm) in a relatively stable slab
- Post-compaction voids under a slab (e.g., after a plumbing leak has washed away subsoil)
- Driveways, paths, and non-structural slabs that have settled but are otherwise sound
- Slab heave correction, with appropriate technique, where a portion of a slab has lifted and resin can re-establish uniform bearing
- As a temporary measure pending full underpinning
In Wagga’s reactive clay environment, foam lifting is most appropriate for newer construction (post-2000, AS 2870-compliant) where the slab was correctly designed but a localised issue (plumbing leak, poor drainage) caused isolated settlement. The underlying reactive clay behaviour is managed by the slab design.
When traditional underpinning is required
- Significant differential movement (more than 25-30 mm across the home)
- Class H2 or E sites where deep reactive clay continues to drive movement
- Heritage or structural masonry homes where the masonry is load-bearing
- Any situation where the cause of settlement is ongoing reactive clay shrinkage and the resin injection depth would not reach stable material
- Timber-framed homes on stumps (where restumping, not resin injection, is the relevant intervention)
- Where a long-term engineering warranty and certification is required (for sale or insurance purposes)
For most Wagga homeowners with significant foundation problems, the deeper reactive clay conditions, the extent of settlement, and the need for long-term certainty point toward traditional underpinning as the appropriate solution.
Cost comparison (indicative, Wagga Wagga)
| Method | Typical cost range | Duration | Warranty |
|---|---|---|---|
| Polyurethane foam lifting | $3,000 to $8,000 | 1 day | 5-10 years (product) |
| Mass concrete underpinning | $12,000 to $30,000+ | 5-10 days | 10-25 years |
| Screw pier underpinning | $10,000 to $25,000+ | 1-4 days | 10-25 years |
Note: costs vary significantly with project scope. These are indicative ranges only.
FAQs
Can I get polyurethane foam lifting done and then do proper underpinning later if needed?
Yes, in most cases. Resin injection can be a useful interim measure for a property that is being prepared for sale or where full underpinning is planned but not yet funded. However, note that the resin does not interfere significantly with subsequent underpinning work, screw piers or mass concrete pits can still be installed alongside or through resin-treated zones.
My contractor recommends foam lifting but I have reactive clay, should I push back?
Yes, you should ask the contractor to explain specifically why foam lifting is adequate for your site conditions. On Class H2 or E reactive clay sites with ongoing moisture-driven movement, foam lifting alone may not address the cause of the problem. If you are uncertain, get a second opinion from an independent structural engineer before proceeding.
Is there a way to tell from outside whether I need foam lifting or full underpinning?
Not reliably without a professional assessment. The pattern and extent of cracking, the floor level differential, and a subfloor inspection together determine the appropriate method. A foundation inspection will give you this information clearly.