Almost all concrete cracks. The question is whether the crack is cosmetic, a sign of movement, or a sign of corroding steel, because each needs a different repair. Using the wrong fix is why so many patched cracks reopen.
Types of concrete cracks
Shrinkage cracks
Fine, often random or map-like cracks that form as concrete dries. Usually cosmetic, especially in driveways and paths.
Settlement and movement cracks
Wider cracks, often with one side higher than the other, caused by ground movement, poor compaction or reactive clay. These can affect house slabs and need investigation. See what causes cracked house slabs.
Corrosion cracks
Straight cracks along the line of the reinforcement, often with rust staining. These mean the steel inside is corroding, the start of concrete cancer.
Structural cracks
Cracks in beams, suspended slabs and load-bearing elements, or cracks that keep growing. These need an engineer.
Repair methods
- Routing and sealing: for non-structural cracks, a flexible sealant keeps water out and allows small movement.
- Epoxy injection: for structural cracks that have stopped moving, low-viscosity epoxy bonds the concrete back together.
- Polyurethane injection: for leaking cracks in basements and retaining walls.
- Break-out and repair: for corrosion cracks, damaged concrete is removed, steel treated and the section rebuilt.
- Slab stabilisation or replacement: where the ground beneath has failed.
Fix the cause first
Movement cracks will reopen if the cause continues. Leaking pipes, poor drainage, trees and reactive soils need to be addressed, and in some cases footings strengthened by underpinning.
DIY or professional?
Hairline shrinkage cracks in paths and driveways can be sealed by a handy homeowner. Cracks in house slabs, suspended slabs, balconies and anything with rust staining or movement should be inspected.
Concrete repairs in Sydney
See our concrete repair service or send us a photo of the crack with a tape measure for scale.
Frequently asked questions
Are cracks in a concrete slab normal?
Fine shrinkage cracks are normal. Wide cracks, cracks with one side higher, or cracks that keep growing should be inspected.
Can epoxy fix a cracked slab?
Epoxy injection can structurally bond cracks that have stopped moving. If the slab is still moving, the cause must be fixed first.
When does a cracked slab need an engineer?
When cracks are wide, growing, in suspended slabs or structural elements, or accompanied by uneven floors and sticking doors.
