Concrete Levelling near you

A proper job starts with a level survey recorded on a sketch, so there is a before and an after, and with a walk around the outside looking for the cause. That means downpipes, the gully, the tap, the irrigation, the trees, the neighbour's drainage and the fall of the ground away from the building. CSIRO's guide is blunt on the first of these: where movement is caused by water service, roof plumbing, sewer or stormwater failure, the remedy is to repair the problem.

Then the question of whether the slab is cracked as well as out of level. Lifting a cracked slab moves the pieces independently and can open the crack further, so the crack treatment has to be part of the plan rather than an afterthought. Queensland's guide is a useful reference for judging the cracking, since it classifies damage by crack width together with the change in offset from a 3 m straight edge and treats Category 3 and 4 cracks to slabs as defects.

And then, if the cause is seasonal, the question of when. A contractor who tells you the slab should be watched across a wet and a dry period before being lifted is giving you good advice, not stalling. CSIRO's own warning about a related practice makes the point: where isolated footings rise and fall with swell and shrink and the owner packs the gap between bearer and pier, the danger is that the next swell pushes the floor up into an accentuated dome and can cause local shear failure in the soil, so if blocking is used it should be a pair of fine wedges with fortnightly monitoring.

CSIRO's guide gives specific, usable advice for protecting a building perimeter on reactive soil. It recommends installing an apron of paving around as much of the building perimeter as necessary, extending outwards a minimum of 900 mm — more in highly reactive soil — with a minimum fall away from the building of 1:60, and finished no less than 100 mm below brick vent bases.

It is equally specific about water. Relocate drainage pipes away from that paving where possible; where that is not practical, replace earthenware pipes with PVC and backfill with the same soil type as the surrounding soil, compacted to the same density. Except where freezing is an issue, remove taps in the building area and relocate them well away from the building, preferably not uphill. Consider a grated drain at the outside edge of the paving on the uphill side, with subsoil drainage beneath it if needed.

And it is specific about the garden. The ideal layout is lawn or plants needing only light watering immediately adjacent to the drainage or paving edge, then more demanding plants, shrubs and trees spread out in that order. CSIRO identifies overwatering through misused automatic watering systems as a common cause of saturation and water migration under footings, and recommends removing garden beds to a safe distance from buildings where such systems are used.

Lifting makes sense when the slab is sound, the drop is creating a trip hazard or sending water the wrong way, and the cause has been identified and addressed. Resin injection is minimally disruptive, usable the same day and can be done in sections, which makes it attractive for driveways and paths where a re-pour would mean losing access for a week.

Living with it is a reasonable choice more often than contractors suggest. A slab that has dropped slightly, is not cracked, is not creating a trip and is not directing water at the house is a cosmetic issue. Queensland's guide accepts a good deal of movement before calling it a defect, and it makes the point that cracking not attributable to the builder's workmanship — trees planted too close to paving, heavy vehicle traffic, excessive garden watering — is not a defect at all. If the cause is your own irrigation, the honest first move is to change the irrigation.

Replacement wins when the slab is badly cracked as well as displaced, because lifting broken concrete produces lifted broken concrete, and when the levels are so far out that lifting would create new problems at a threshold or a step. It is also the moment to fix the base, the falls and the jointing properly, which a lift cannot do.

A concrete levelling quote should name the cause, not just the cure. Ask for the level survey, the contractor's view of why the slab dropped, what happens to the cracks, how many injection points and where, what the target level is, and what guarantee is offered — and specifically whether that guarantee survives further ground movement, because on a reactive site it usually does not.

Get the drainage and plumbing work quoted alongside it, or at least scheduled before it. CSIRO's guidance is that where movement is caused by a water service, roof plumbing, sewer or stormwater failure, the remedy is to repair the problem, and that erosion damage should be made good with soil of the same classification compacted to the same density. Lifting a slab over ground that is still being saturated is money spent twice.

The Australian Consumer Law guarantees apply to the service: acceptable care and skill, fitness for any stated purpose, supply within a reasonable time. Queensland's guide also notes that slab and footing movements caused by the owner's failure to maintain the site are not defects, which cuts both ways and is another reason to fix the water first. Use LokalMatch to get several opinions on the same slab, and treat any contractor who quotes a lift without looking at your downpipes as an incomplete answer.