What We Fix
What We Fix
Sunken Concrete Slabs
Why is my concrete floor sinking — and can it be fixed without ripping it up?
Concrete floor slabs sink. It happens gradually — a slope you didn't notice until a door started sticking, a gap that opened at the skirting, a crack that appeared across the tiles. The slab hasn't broken. The ground beneath it has moved.
Most people assume the only fix for a sunken concrete slab is to jackhammer the floor, rip up the tiles, dig out the ground, recompact, repour, and wait for it to cure. Weeks of work. House unliveable. But here's what 15,000+ jobs have taught us: the concrete is almost never the problem. The ground underneath is. Fix the ground, and the slab goes back where it belongs.
The signs below will help you work out what's happening beneath your floor — and whether your sunken concrete slab can be relevelled without replacing it.
What are the symptoms of sunken concrete slabs?
Some signs are obvious. Others show up as problems you didn’t connect to the floor slab. Here’s what to look for — and why it’s happening.
Sloping or Uneven Floor
Place a ball on the floor. If it rolls, the slab has dropped on one side. You might feel it underfoot — a lean toward one corner, a slope across the room. Furniture wobbles. A spirit level confirms what your feet already told you. The most common cause is reactive clay — soil that swells when it’s wet and shrinks when it dries. Each weather cycle shifts the ground beneath the slab a little further. If the slope has appeared gradually, the ground is still moving.
Doors Sticking or Not Closing
A door that used to close fine and now drags, jams, or swings open on its own. The door isn’t the problem — the floor beneath it has shifted. When a slab drops unevenly, the door frame goes with it. If multiple doors in the same area are affected, the slab has moved significantly. Poor compaction during construction is a common driver — the filled side of the site settles, the cut side doesn’t, and the floor slopes toward the fill.
Gaps at Skirting Boards
A gap between the bottom of the skirting and the floor that wasn’t there before. The skirting is fixed to the wall. The floor has dropped away from it. Run your finger along the base — if the gap is wider at one end than the other, the slab has tilted rather than dropped evenly. Water runoff from poor drainage or leaking downpipes washes fine particles out of the soil beneath the slab, leaving voids. The concrete drops into the gap.
Cracked Floor Slab or Tiles
Cracks running through floor tiles, or visible cracks in an exposed concrete floor. Concrete doesn’t bend — when the ground beneath it drops away, the slab spans an unsupported gap and cracks. Tree roots growing under slabs are a common culprit: when the tree is removed or the roots die back, the space they occupied becomes a void. If the cracks are getting wider, the void beneath is getting bigger.
A Hidden Plumbing Leak
A leaking pipe you can’t see. Water mains, sewer lines, and stormwater drains run beneath floor slabs — when one cracks or disconnects, water saturates the soil for months before anyone notices. The ground softens, loses its bearing capacity, and the slab sinks into it. If your water bill has crept up unexpectedly, a leak under the slab is worth investigating. Fix the water source first, or the floor will just sink again.
Sunken Driveway, Garage Floor, or Outdoor Slabs
The driveway has dropped away from the garage, or the garage floor slopes toward the roller door. Water pooling on paths instead of draining. A pool surround pulling away from the coping. The ground beneath outdoor concrete is vulnerable to the same forces — reactive clay, poor compaction, water erosion. If it’s happening outside, the same thing may be happening beneath your floor.
How to spot a sunken concrete slab
How to fix sunken concrete slabs
Non-Invasive. Laser-Monitored. Guaranteed.
No Jackhammers. No Tiles Ripped Up. Walk on It Today.
Concrete relevelling, also known as slab jacking, lifts your floor back towards level through coin-sized holes — no jackhammers, no tiles ripped up, no concrete trucks. As the foundation relevels, you'll notice doors closing again, furniture sitting flat, and the slope underfoot disappearing. Most jobs are done in a few hours, not weeks.
Slab replacement works — but it means jackhammering the floor, ripping up tiles, digging out the ground, recompacting, repouring, and weeks of curing. Here's what 15,000+ jobs have taught us: the concrete almost never needs replacing. The ground beneath it does.
GeoPoly™ SJ120 — a controlled-expansion resin — is injected through the access holes directly into the ground beneath the slab. The resin fills the voids, compacts the weakened soil, and expands with precision to lift the concrete back towards level. Laser levelling equipment monitors every millimetre of movement in real time. The resin hardens within minutes — tougher than the original ground.
Need your slab relevelled? Learn about our concrete relevelling solution.
Structural Engineers · Licensed Builders · Skilled Technicians
Help & Advice
Articles to help you understand sunken concrete slabs and what to do next.
ConcreteReplacing a Concrete Driveway
Your concrete driveway takes a battering on a daily basis. You drive your vehicle over it.
ConcreteRelevel Your Driveway — Don't Replace It
Nine times out of ten, the slab isn't the problem. The concrete is fine. The ground underneath it has dropped.
Industry AdvicePolyurethane Applications
Polyurethane was invented in the 1930s by German Industrial chemist, Dr Otto Bayer. He designed it as a substitute for rubber, a scarce material during World War 2 and was used on a limited scale as aircraft coating during the same war.
Floor LevellingSelf-Levelling Compound Explained
If you're planning a renovation, self-levelling compound might seem like the perfect fix for uneven floors. After all, it's widely recommended by builders and tilers for its quick application and smooth finish.
Floor LevellingLevelling a Sloping Floor
A sloping floor is easy to dismiss—until it gets worse. What starts as a slight tilt can turn into misaligned walls, sticking doors, or even structural instability.
Common questions about sunken concrete slabs
The questions homeowners ask us most often.
