Guide
Two different trades, one confusing name
Updated 17 August 2026
Type resin injection into a search bar in Australia and you will be shown two industries that have almost nothing in common. One pumps resin into a crack or joint inside a concrete element to stop water. The other pumps resin into the ground beneath a slab or footing to compact weak soil, fill voids and lift the structure back to level. Same two words, different trade, different materials, different licence, different problem entirely.
The confusion is not the customer's fault. The ground-engineering brands are national, well established and rank strongly for the bare term — Mainmark and Resinject are genuinely good at what they do and have documented project libraries to prove it — while the leak-sealing trade has never bothered to write the distinction down clearly. So homeowners with a wet garage wall get routed to subsidence contractors, and people with a sunken driveway ring waterproofers.
The short version: if the problem is water, you want injection into the concrete, and that is us. If the problem is level — a sunken driveway, doors and windows binding, a step where there did not use to be one, a warehouse floor you can see the fall in — you want ground improvement, and you want it from a ground-engineering specialist rather than from a waterproofer.
One question separates them: is your problem water, or level?
Almost every misdirected enquiry we receive resolves on that single question, and most people can answer it from where they are standing.
Water problems present as damp, staining, salt bloom, beading, weeping or running flow, and they usually correlate with rainfall or the wet season. Level problems present as height differences, binding doors, tapered gaps at skirtings and window heads, drummy hollow-sounding slab areas, and they usually correlate with drought, tree growth, a plumbing leak, or the years since the slab was poured.
A minority of jobs have both. Those are dealt with further down, because the order the two trades attend in matters more than which one you call first.
- Damp patch, tide mark, salt bloom, beading or running water on concrete — leak sealing
- Wet only during and after rain, dry in winter — leak sealing
- Water rising through the floor along the line where the slab meets the wall — leak sealing
- A step, lip or fall in a driveway, path or warehouse floor — ground improvement
- Doors and windows binding, tapering gaps at skirtings — ground improvement
- Slab sounds hollow or drummy when tapped, with no water present — ground improvement
- A cracked slab that is both out of level and passing water — both trades, in a specific order
Where the resin actually goes
The two methods look superficially similar on site — a pump, a hose, small holes, a technician watching a gauge — which is most of why the names have blurred. Everything under the surface is different.
In leak sealing, holes are drilled at 45 degrees to the face, offset from the crack line by roughly half the element thickness so the hole intersects the crack at mid-depth, and driven to about two-thirds to three-quarters of the thickness. Never through: break out the far face and you lose all pressure and inject into the room or the ground beyond. In ground improvement, the hole is deliberately taken right through the slab, because the slab is not the target — the soil beneath it is.
| Leak sealing (what we do) | Ground improvement (a different trade) | |
|---|---|---|
| Target | The crack, cold joint or tie hole inside the concrete element | The subgrade soil beneath the slab or footing |
| Hole | 13 mm at 45 degrees, drilled to two-thirds to three-quarters of thickness, never through | Typically 12–16 mm, taken right through the slab, patched afterwards |
| Material | Hydrophobic or hydrophilic polyurethane, acrylate gel at 10–50 mPa·s, structural epoxy, or microfine cement | Two-component, often heated, high-density structural polyurethane or geopolymer |
| What makes it set | Contact with water in the crack, or a two-part chemical reaction | A two-part reaction in a heated rig; cures in minutes |
| Expansion | Free-rise 8–30x is a lab figure; real confined expansion is roughly 3–8x | Very high free rise, but the working principle is expansion pressure against soil confinement |
| Pressure | 35–140 bar for mechanical-packer polyurethane; 2–15 bar for acrylate and curtain work | Governed by soil resistance and monitored lift, not by a target gauge pressure |
| Control measure | Resin appearing at the next packer along, confirming the crack is connected | Continuous laser or digital level monitoring during the lift, in a planned injection sequence |
| What it achieves | A sealed water path through the element, for the life of the structure | Compacted soil, filled voids and a controlled lift back toward level |
| Back in service | Packers stay in 24 hours before cut-back and make good | Most residential slab lifts complete in a day; driveways often trafficable within hours |
Ground-improvement injection will not stop a drop of water
This needs saying plainly because it is occasionally implied otherwise, usually by accident rather than design. High-density structural polyurethane injected into the subgrade is doing a mechanical job against soil. It is not a waterproofing material, it never enters the crack, and it is not formulated, certified or warranted as a water barrier.
Even when it fills a void under a slab — and filling voids is exactly what it is for — it does not seal the crack, the kicker joint or the construction joint that the water is actually coming through. Those paths are inside the concrete, above the resin. Water under head will keep finding them.
None of that is a criticism of the ground-engineering firms. Mainmark, Resinject and the re-levelling specialists solve a genuine and difficult engineering problem, they carry the geotechnical judgement and the heated two-component rigs to do it, and for real subsidence they are the right call and we will say so. Their published material simply addresses subsidence, voids and load transfer, because that is the discipline. Water ingress is a different discipline with different chemistry and a different standard of proof.
And crack injection will not lift anything
The reverse is equally true and worth stating, because it protects you from us as much as from anyone else.
A hydrophobic polyurethane foam confined inside a 0.4 mm crack, expanding perhaps three to eight times against the crack faces, has no bearing role whatsoever. It is a plug keyed into a water path — and because water on the substrate acts as a bond breaker, the seal is mechanical rather than adhesive. It does not transfer load to the ground and it will not raise a slab by a millimetre.
Structural epoxy is the strongest thing we inject and it still lifts nothing. Cured compressive strength in the 60 to 90 MPa range and a bond that exceeds the tensile strength of the parent concrete mean a correct epoxy repair restores monolithic action across a dormant crack — the concrete will fail beside the old crack rather than in it. That is restoration of what the element already had. It is not additional capacity, and it is certainly not lift.
Lifting the slab does not fix why it sank
This is the part that gets left out of the sales conversation, and it is the reason a slab can be re-levelled beautifully and start moving again two summers later.
Ground-improvement injection compacts weak soil and fills voids. It does not address why the soil was weak or why the void formed. In South East Queensland the usual causes are reactive clay cycling through wet and dry seasons, a leaking sewer or stormwater line washing fines out from under the slab, poorly compacted fill from the original build, mature trees drawing moisture out within the root zone of the footing, and site drainage discharging against the building.
Unless the cause is found and corrected first, the slab settles again — and the client, quite reasonably, blames the last contractor who touched it. Correcting the cause is a separate cost, it is usually mandatory rather than optional, and any competent ground-engineering specialist will say so before quoting the lift. If one does not, that is the question to ask before signing.
- Find the cause before pricing the liftCamera and pressure-test the sewer and stormwater under and around the slab. A leaking service is both the most common cause of localised washout and the cheapest of the causes to fix.
- Deal with the water regimeSite drainage, downpipe discharge points, falls away from the building and any subsoil drainage. Reactive clay moves with moisture, so stabilising the moisture regime around the footing is doing real geotechnical work, not landscaping.
- Consider the vegetationMature trees within the influence zone of a footing extract moisture and shrink reactive clay. Removing one can also cause heave as the soil rehydrates, so this is an engineer's call, not a chainsaw call.
- Then lift, in sequence, with monitoringThe lift itself is controlled by injection sequence and real-time level monitoring, not by resin volume. Lifting too fast or in the wrong order cracks the slab, which is how a re-levelling job creates the crack a leak-sealing contractor is later asked to inject.
Where it amounts to underpinning, licensing and certification apply
There is a threshold in ground-improvement work where the job stops being a cosmetic re-level and becomes structural support to a footing. At that point it is effectively underpinning, and the compliance obligations change.
Engineer involvement and, in many cases, certification is likely to be required, and building approval may be as well. In Queensland, trade work valued over $3,300 including labour, materials and GST requires the appropriate QBCC contractor licence, and residential work over that threshold also triggers Home Warranty Insurance obligations. The precise licence class and approval pathway depends on the scope, so it is verified per job rather than assumed.
The practical version for an owner: if a resin injection proposal is going to change how a footing is supported, ask for the engineer's involvement in writing and ask which licence class the work is being performed under. A specialist will have the answer ready. It is the same standard we hold ourselves to when a leak-sealing scope touches a structural element.
Five checks that tell you which one you have
- Does it correlate with rain?Damp that arrives during or after rainfall and recedes in dry weather is a water path. Movement does not switch on and off with a storm. If the wall or floor is only wet in the wet season, you are looking at leak sealing, not ground engineering.
- Is there a level difference you can measure?Put a two-metre straightedge or a long spirit level across the area, or roll a marble. A visible step, lip or consistent fall is a settlement symptom. A wet patch on a floor that is dead flat is not.
- Is water actually passing through the crack?Dry the crack, then watch it during or immediately after rain. Water emerging from the crack line, beading along it, or salt bloom tracking away from it means the crack is a live water path. Efflorescence is not damage in itself, but it is proof that water has been moving through.
- Does the slab sound hollow?Tap across the slab with a hammer handle or a steel bar. A drummy, hollow note over an area suggests a void beneath, which is ground-improvement territory. Note that drummy concrete can also mean internal delamination from corrosion, which is a third answer again and belongs to a concrete repair contractor.
- Has something changed nearby?A tree removed or newly mature, a pool installed, a driveway re-poured, a plumbing repair, a flood event, a long drought broken. Settlement almost always has a story attached to it. Water ingress usually does not — it has been there quietly since the building was poured and only became your problem when a finish went in.
The jobs that genuinely need both, and the order they go in
A leaking sewer under a slab is the classic case. The escaping water washes fines out of the subgrade, a void forms, the slab settles into it and cracks, and the crack then passes water into the space below. That single defect produces a plumbing problem, a geotechnical problem and a waterproofing problem simultaneously, and each is worthless without the other two.
The order is not negotiable, because doing it out of sequence means paying twice. Fix the service. Establish that the ground has stopped moving. Improve or re-support the ground if it needs it. Only then seal the crack — because injecting a crack in a slab that is still settling is exactly the case where the repair holds and the concrete cracks again beside it.
Where movement is uncertain rather than obvious, tell-tales or crack monitors read over 4 to 12 weeks across a temperature and moisture cycle will settle the question for a fraction of what a second repair costs. It feels slow. It is cheaper than injecting twice.
What each one costs, in indicative bands
These are indicative South East Queensland bands rather than quotes, and both trades price on drivers that only appear on site. They are here so you can sanity-check a proposal, not so you can budget from a web page.
| Work | Indicative band |
|---|---|
| Site attendance and set-up minimum, leak sealing, business hours metro | $450 – $900 |
| Polyurethane crack injection, accessible and straightforward | $150 – $450 per linear metre |
| Construction or cold joint injection | $200 – $500 per linear metre |
| A single basement or garage wall crack, complete with make good | $900 – $2,500 |
| Slab lifting and void filling, typical residential | $2,500 – $15,000 |
| Slab lifting and void filling, large commercial | $30,000 – $100,000+ |
| Correcting the cause of settlement (service repair, drainage, vegetation) | Separate cost, and usually mandatory |
If it turns out to be water after all
A cracked slab that leaks is our work rather than a ground engineer's, and it is one of the more common things we are called to in Brisbane, Logan and the Gold Coast hinterland — undercroft garages, suspended slabs leaking to the level below, and slab-to-wall kicker joints letting water up along the base of a wall.
Two things are worth knowing before you worry. First, fine cracking in concrete is normal: AS 3600, the Australian concrete structures standard, allows for crack widths broadly in the 0.1 to 0.4 mm range at serviceability depending on the element and its exposure classification. The existence of a crack is not by itself a defect. Second, the visible crack is frequently not the entry point — water tracks laterally between the structural slab and its topping, or between the membrane and the concrete, and exits at the weakest point metres away. Mapping the path matters more than injecting quickly.
If you are still not sure which of the two trades you need, the diagnostic will ask you the seven questions that separate them and hand you back a specification you can put out to tender — including to the ground-engineering firms, if that is where the answer lands.
Questions we actually get asked
- I searched resin injection and got both. How do I tell which industry I am looking at?
- Look at where the resin is going. If the page talks about cracks, joints, packers, negative-side waterproofing, hydrostatic pressure and stopping water, it is leak sealing. If it talks about lifting, re-levelling, voids, subgrade, settlement and geotechnical assessment, it is ground improvement. If a page talks about both as though they are one service, be careful — they use different materials, different rigs and different competencies, and very few businesses genuinely hold both.
- Can polyurethane crack injection lift my sunken driveway?
- No. The polyurethane used for leak sealing is injected into the crack itself and confined by the crack faces, expanding roughly three to eight times against that confinement. It has no bearing function and does not reach the soil. Lifting requires a high-density two-component structural polyurethane or geopolymer injected into the subgrade through a heated rig, in a planned sequence, with continuous level monitoring during the lift. That is a different material and a different trade.
- The re-levelling contractor said the resin also seals against water. Is that right?
- Not in the sense you probably mean. Filling voids under a slab does change how water moves through the ground beneath it, and a contractor may be describing that honestly. But the injected mass is not a waterproofing product, it does not enter or seal the crack or joint that water is coming through the slab at, and it carries no waterproofing certification. If your actual symptom is water appearing on top of or through the slab, ask the question directly: will this stop water coming through that crack? The honest answer is no.
- My slab has cracked, it is out of level, and it leaks. Do I need both trades?
- Probably, and the order matters. Establish the cause first — a camera and pressure test on the sewer and stormwater is where that usually starts, because a leaking service is both a common cause of washout and the cheapest cause to correct. Then let the ground engineer deal with the voids and the level. Only then seal the crack. Injecting a crack in a slab that is still settling is precisely the case where the repair holds and the concrete cracks again a few millimetres away, and you pay for the injection twice.
- Do I need an engineer for a slab lift?
- For anything that supports a footing rather than just re-levelling a path or a driveway slab, yes. Where the work amounts to underpinning, engineer involvement and possibly certification is likely to be required, and building approval may be too. It is verified per job because scope and state requirements differ. Separately, an engineer is the right person to advise on tree removal near a reactive-clay footing, because removing a mature tree can cause heave as the soil rehydrates.
- Is this QBCC-licensed work in Queensland?
- Trade work valued over $3,300 including labour, materials and GST requires the appropriate QBCC contractor licence, and residential work over that threshold also brings Home Warranty Insurance obligations. Which licence class applies depends on the scope — waterproofing is its own trade class, while structural concrete repair and ground support work can fall elsewhere. Ask any contractor in either trade for their licence number and check it against the QBCC public register. It takes about a minute and it is the cheapest due diligence available to you.
- Should I worry about a crack in my slab that is not leaking and not out of level?
- Usually not. AS 3600 allows for crack widths broadly in the 0.1 to 0.4 mm range at serviceability depending on the element and its exposure classification, so fine cracking as concrete shrinks and cures is expected rather than defective. The two questions that matter are whether water is passing through it and whether it is getting wider. Fit a crack monitor and read it over a few months if you want a number instead of an opinion — that is cheap, and it is the same evidence an engineer would want.