If you’re responsible for a commercial building or a strata property in Sydney, concrete repair is one of those jobs that eventually lands on every property manager’s desk. The question usually isn’t whether it’s needed – it’s what type of repair you’re actually dealing with, how long it will take, and what it’s reasonably going to cost.
This guide walks through the main types of concrete repair we’re asked about most often, what the process typically looks like, and the kind of timeframes and cost ranges you can expect. It’s written for property managers, strata committees, and commercial property owners who need a practical understanding before they start getting quotes, not a technical manual for engineers.
What types of concrete repair are there?
Concrete repair isn’t one job – it’s a category that covers several distinct problems, each with its own repair method. Here’s the breakdown.
Concrete cancer repair. This is the big one in Sydney’s older building stock. Reinforcing steel corrodes inside the concrete, the rust expands, and the concrete cracks and spalls from the inside out. Repair involves breaking out the affected concrete, treating or replacing the corroded steel, and reinstating the surface with a bonding agent and repair mortar. We cover this in detail in our dedicated guide to concrete cancer in Sydney carparks and balconies.
Spalling repair. Spalling is the visible symptom – chunks of concrete flaking, cracking, or breaking away from the surface. It’s often caused by concrete cancer, but can also result from freeze-thaw type stress (less common in Sydney’s climate), poor original mix design, or physical impact damage. Repair depth depends entirely on how far the deterioration extends behind the visible surface.
Joint failure repair. Expansion joints and construction joints are designed to let concrete move without cracking. When the joint sealant fails, breaks down, or was installed incorrectly, water gets into the joint and the surrounding concrete, accelerating deterioration and often leading to cracking either side of the joint line. Repair involves removing the failed sealant, preparing the joint properly, and reinstating with a product rated for the movement and exposure the joint experiences.
Slab repair. This covers everything from surface cracking and settlement cracking through to more significant structural repairs where a slab has moved, dropped, or cracked through its full depth. Car park slabs, driveway slabs, and structural floor slabs each have different repair considerations depending on load requirements and access.
Crack injection. For cracks that aren’t associated with active corrosion but need to be sealed to stop water ingress or restore structural continuity, epoxy or polyurethane resin injection is a common and effective method. It’s a more contained repair than breakout and reinstatement, and is often appropriate for narrower, stable cracks.
Waterproofing-linked repair. A large share of concrete repair work in Sydney exists because a waterproofing membrane failed somewhere upstream – on a balcony, a planter box, a roof deck, or a car park slab. Repairing the concrete without addressing the waterproofing failure that caused the damage is a false economy; the problem simply returns.
| Repair type | Typical cause | Typical method | Best suited to |
|---|---|---|---|
| Concrete cancer repair | Steel corrosion, carbonation, chloride ingress | Breakout, steel treatment, polymer mortar reinstatement | Carparks, balconies, facades |
| Spalling repair | Corrosion, impact, poor mix design | Breakout and reinstatement to sound concrete | Slabs, columns, beams |
| Joint failure repair | Sealant breakdown, poor original install | Joint preparation and resealing | Expansion and construction joints |
| Slab repair | Settlement, cracking, structural movement | Ranges from surface patching to structural intervention | Car park and driveway slabs |
| Crack injection | Shrinkage, movement, non-corrosive cracking | Epoxy or polyurethane resin injection | Stable, non-structural cracks |
| Waterproofing-linked repair | Failed membrane allowing water ingress | Concrete repair plus membrane reinstatement | Balconies, planter boxes, decks |
What the repair process actually looks like
Most legitimate concrete repair jobs, regardless of type, follow a broadly similar sequence.
Assessment. A proper assessment involves visual inspection, hammer testing (sounding) to identify delamination that isn’t visible on the surface, and in some cases core sampling to check the depth of carbonation or the condition of the reinforcing steel. This step determines the real scope of the job – and it’s the step that gets skipped by contractors who want to quote quickly and cheaply.
Scoping and quoting. Once the assessment is complete, a proper scope of works identifies exactly which areas need treatment, the repair methodology for each, the materials specified, and the standards the work will be carried out to, including AS 3600 for concrete structures. Vague one-line quotes are a red flag at this stage.
Preparation. The affected concrete is broken out to sound material – concrete that isn’t cracked, delaminated, or contaminated with chlorides. Any exposed reinforcing steel is cleaned, and where corrosion has reduced the steel’s cross-section significantly, it may need to be supplemented or replaced.
Reinstatement. A bonding agent is applied, followed by a repair mortar – often a polymer-modified mortar selected for its bond strength, shrinkage characteristics, and durability in the specific exposure environment. For larger structural repairs, this may involve formwork and a poured repair rather than a hand-applied mortar.
Finishing and protection. Depending on the location and exposure, the finished repair may be coated, painted to match the surrounding surface, or left as an exposed repair where appearance isn’t the priority. Where waterproofing was the underlying cause, membrane reinstatement happens as part of the same job.
Realistic timeframes
Timeframes vary enormously depending on scope, but as a general guide:
Small, contained repairs – a handful of spalled areas, a section of failed joint, isolated crack injection – typically take a few days to a week once access is arranged.
Medium-scope carpark or balcony remediation, covering multiple locations across a building, commonly runs from two to six weeks, depending on the extent of breakout required and whether waterproofing reinstatement is part of the scope.
Larger structural remediation projects – full carpark soffits, extensive facade work, multi-building strata remediation – can run from several months to over a year, particularly where staging around occupied buildings, scaffolding or access equipment, and council or engineering sign-off are involved.
Realistic cost ranges
Cost is genuinely scope-dependent, and any contractor giving you a firm figure before a proper assessment should be treated with caution. That said, as a rough guide for Sydney commercial and strata work: small, isolated repairs often sit in the low thousands of dollars. Medium-scope carpark or balcony remediation across multiple units commonly runs from the tens of thousands into six figures, depending on the building. Large-scale structural remediation projects can run well into six or seven figures once access, engineering, and staging are factored in.
The single biggest driver of cost blowouts is deferred maintenance – concrete damage that’s left unaddressed continues to spread, and the repair required in year three is almost always more expensive than the repair that would have been required in year one.
Frequently asked questions
How do I know if I need concrete repair or a full remediation project?
A proper assessment by a specialist contractor will tell you. Isolated cracking or a small area of spalling might be a contained job. Widespread rust staining, hollow sounds across multiple areas, or damage across several storeys usually points to a larger remediation scope.
Does insurance cover concrete repair?
This depends heavily on the cause and your policy. Gradual deterioration such as concrete cancer is typically not covered as a maintenance issue, whereas damage from a specific insured event may be. Speak with your strata insurer or broker directly about your specific circumstances.
Can repairs be done without disrupting building occupants?
In most cases, yes. Staged works, noise and dust management, and clear communication with residents or tenants are standard practice for an experienced remedial contractor working in occupied buildings.
What standards should the work meet?
Commercial concrete repair in NSW should be carried out with reference to AS 3600 (Concrete Structures), and where tiled or waterproofed surfaces are involved, AS 3958 (Ceramic Tiles) is also relevant.
Stakat Building carries out concrete repairs across commercial buildings, strata complexes, and industrial properties throughout Sydney, including concrete cancer remediation, spalling repair, joint repair, slab repair, and crack injection. If you’d like an honest assessment of what your building actually needs, we offer a free site assessment.