Service · Sunken concrete
Slab lifting & concrete levelling in Melbourne
A driveway that has dropped away from the garage. A path with a lip you keep catching your toe on. A patio now sloping back towards the house instead of away from it. In most cases the concrete is perfectly sound — it is the ground underneath that has gone, and that can be corrected without breaking anything out.
What we lift
- Driveways — particularly where the slab has dropped at the crossover or pulled away from the garage apron.
- Garage and shed floors — including slabs that have sunk unevenly and now pond water at one end.
- Paths and porches — trip hazards where two slabs have parted company, and entry slabs that have tilted back toward the front door.
- Patios, alfrescos and pool surrounds — where the fall has reversed and water now runs at the house.
- Internal slabs in garages, workshops and warehouses, where breaking out and repouring means shutting the space down.
Why concrete sinks in Melbourne
The concrete is rarely the problem. Something has changed the soil underneath it, and there are four causes behind the overwhelming majority of jobs:
- Poorly compacted fill. Very common in growth-corridor estates, where sites were cut and filled during subdivision. Fill settles for the first five to fifteen years, and anything poured on it goes down with it.
- Escaping stormwater. A cracked stormwater line, a disconnected downpipe or a downpipe discharging straight onto soil beside the slab washes the fine particles out of the ground and leaves a void. This is the most common cause we find, and the most important one to fix.
- Reactive clay shrinking. Through a dry summer, clay under an unshaded driveway loses moisture and contracts, and the slab drops with it. In the west and south-east this can partly reverse in winter, which is why some slabs appear to move seasonally.
- Service trenches. Water, sewer and gas trenches backfilled without proper compaction leave a soft line under the slab, and the slab cracks and dips along exactly that line.
How the job runs
- Assessment. Levels taken across the slab, and a look for the water source — downpipes, stormwater pits, the crossover, the irrigation. If a leak is driving it, that gets fixed first or the lift is wasted money.
- Drilling. A grid of small holes, typically 10 to 16mm, through the slab. No excavation and no removal of anything.
- Injection. Expanding polyurethane resin is injected in sequence. It fills voids, compacts the surrounding soil, then lifts. Laser levels on the surface control the raise to the millimetre.
- Finishing. Holes are patched flush and matched as closely as concrete allows. Most residential jobs are two to five hours.
- Back in service. The resin reaches most of its strength within about fifteen minutes. You can drive on the slab the same day.
What slab lifting costs in Melbourne
$2,500 – $8,000 for a typical residential slabA single sunken path or porch section commonly runs $2,500 to $4,000. A standard double driveway sits around $4,000 to $8,000 depending on the void volume and how far it has to come up. Priced primarily on the amount of resin the ground takes, which is why an on-site look matters — a slab sitting on a large washout consumes far more than one that has settled evenly. Typically about half to two-thirds the cost of breaking out and repouring.
Indicative range only, based on typical jobs in this area. Access, soil conditions and the extent of movement change the number — a fixed price follows an on-site inspection.
When we will tell you not to bother
Slab lifting is not always the right answer, and we would rather say so up front:
- The concrete has failed, not just sunk. Badly spalled, crumbling or broken into many pieces — it has no stiffness left to lift as a unit. Replace it.
- The leak has not been fixed. Lifting over an active stormwater or sewer leak will sink again. The plumbing comes first.
- It is the house, not the slab. If the driveway has dropped and the brickwork above the windows is cracking, the slab is a symptom of something larger. That is an underpinning conversation, and lifting the driveway would be treating the least important part of it.
Where we do most slab lifting
The growth-corridor estates, where cut-and-fill sites and reactive clay combine — the same suburbs where we do most of our underpinning work:
- Caroline Springs 3023Western Growth Corridor
- Melton 3337Western Growth Corridor
- Point Cook 3030Wyndham
- Tarneit 3029Wyndham
- Werribee 3030Wyndham
- Hoppers Crossing 3029Wyndham
- Truganina 3029Wyndham
- Taylors Hill 3037Western Growth Corridor
- Deer Park 3023West
- Wyndham Vale 3024Wyndham
- Cairnlea 3023West
- Williams Landing 3027Wyndham
- Glen Waverley 3150Eastern Suburbs
- Berwick 3806South-East Growth Corridor
- Narre Warren 3805South-East Growth Corridor
- Cranbourne 3977South-East Growth Corridor
- Clyde North 3978South-East Growth Corridor
- Pakenham 3810South-East Growth Corridor
Slab lifting questions, answered properly
How does slab lifting actually work?
Small holes, usually 10 to 16mm, are drilled through the sunken slab on a grid. A two-part polyurethane resin is injected through them. The resin expands underground within seconds, first filling the void beneath the slab, then compacting the loose soil around it, and finally generating enough pressure to raise the slab. Laser levels on the slab surface tell the operator when to stop at each injection point. The holes are patched, and the slab carries traffic again the same day.
Is slab lifting the same as underpinning?
No, and confusing them is expensive. Slab lifting raises a slab back to level by filling and compacting the ground directly beneath it — it is a soil treatment. Underpinning transfers a building load down to competent ground or bedrock through piers — it is a structural repair. A sunken driveway or garage floor is a slab lifting job. A cracking house on moving clay is an underpinning job. Resin injection is sometimes used underneath houses too, but that is a different design, at greater depth, and it is not what lifting a path involves.
How long does it last?
The resin itself is inert, does not absorb water and does not break down, so it will not degrade. Whether the slab stays level depends entirely on whether the cause was fixed. Lift a slab that sank because of a leaking stormwater line and leave the leak, and it will sink again — the resin is not the failure, the water is. That is why we look for the water source before quoting. Where the cause was one-off, such as poorly compacted fill settling after construction, the correction is effectively permanent.
Is it cheaper than replacing the concrete?
Usually about half to two-thirds the cost of breaking out and repouring, and the difference widens on larger areas or where access for a truck and excavator is poor. The bigger practical advantages are time and disruption: lifting a driveway is a few hours and you can drive on it that afternoon, where a replacement is demolition, spoil removal, formwork, a pour and then a week or more of curing before it takes a vehicle. Replacement wins when the concrete itself is badly broken up rather than simply sitting too low.
What causes concrete around a house to sink?
Almost always something moving the soil underneath rather than anything wrong with the concrete. The usual culprits in Melbourne are poorly compacted fill placed during construction settling over the first ten years, stormwater escaping from a cracked pipe or a downpipe discharging beside the slab and washing fines out of the soil, reactive clay shrinking through a dry summer, and vibration from heavy vehicles on a driveway built over service trenches. Tree roots are a common suspect but a less common actual cause.
Can you lift a slab that is already cracked?
Often yes. A slab that has cracked into two or three large pieces can usually be lifted, with the injection sequenced so the pieces come up together and the crack closes rather than steps. A slab broken into many small pieces, or one where the reinforcement has corroded through, has lost the stiffness needed to lift as a unit — at that point replacement is the honest answer and we will say so rather than take the job.
Related reading:Resin injection vs underpinning ·Can a leaking pipe make a house sink? ·Underpinning & foundation repair