PERTHFixing concrete spalling: trades, methods and AS 3600
Rectifying concrete spalling in Perth: why patching fails, proper corrosion-arrest repair, the structural engineer and concrete remediation specialist
Concrete spalling does not fix itself and it does not stop on its own. Patching over it without addressing the rusting steel underneath is worse than doing nothing, because it hides an accelerating problem. Here is how it is actually repaired, who is qualified to do it, and the standards that govern the work.
Why a patch job fails
The instinct is to fill the hole and paint over it. The problem is that the steel is still rusting behind the patch, and rust keeps expanding, so the new material is pushed off within a few years, often taking sound concrete with it. Worse, patching one area can shift the electrochemical balance and accelerate corrosion in the concrete right next to the repair, a well-known effect called the incipient anode or halo effect. Concrete repair is not filling; it is arresting a corrosion process.
How it is properly done
Genuine remediation follows a sequence. The affected concrete is broken back until sound material and clean steel are reached, going behind the bars, not just to their face. The exposed reinforcement is cleaned of rust, and where it has lost significant section it is supplemented or replaced. The steel is treated or a corrosion-inhibiting system applied. The section is rebuilt with a repair mortar matched to the parent concrete, and the surface is often protected against further chloride and carbonation ingress.
On larger or chloride-contaminated structures, engineers sometimes specify cathodic protection, an electrical system that halts the corrosion across the whole element rather than area by area. Which approach suits depends on how far the chloride has penetrated and how much steel is left, which is why it is investigated and designed rather than chosen off a shelf.
Who is legally and practically required
A structural engineer assesses and designs the remediation. Concrete durability and capacity sit under AS 3600, and assessing how much reinforcement section remains, and whether the element is still adequate, is engineering work that depends on testing, not observation. On a suspended balcony or slab, an engineer's sign-off is what tells you the structure is safe again.
A concrete remediation specialist, or a registered building contractor working to the engineer's specification, carries out the work. Concrete repair is a specialised trade with its own materials and methods, and in WA building work over $20,000 must be contracted by a builder registered with the Building Services Board. Check the registration, as set out in our guide on verifying a builder.
The standards that govern the repair
The controlling standard is AS 3600, the concrete structures standard, which sets durability requirements including minimum cover to reinforcement by exposure classification, and is the deemed-to-satisfy reference for concrete under the National Construction Code, published by the Australian Building Codes Board. Loads are assessed under the AS 1170 series. A remediation that restores cover to the AS 3600 requirement for a coastal exposure classification is one that will last; one that puts the steel back under the same inadequate cover that failed the first time is buying a few years, not fixing the problem.
What it means for a buyer or owner
If you are buying a property with visible spalling on a structural element, get the building inspection first, then an engineer's investigation if it is flagged, and price the remediation before committing. If repairs have already been done, ask for the engineer's report, the specification, and evidence the cover was restored to the current exposure requirement, not merely filled.
In strata, a spalling balcony or common-property slab is shared cost, and it can be substantial. Where an owner has been landed with the consequence of a builder's inadequate original cover on a newer building, it can become a building service complaint or an expert witness matter, and the WA disputes process sets out the route.
Why the repair is harder than it looks
Concrete spalling is one of those defects where the visible damage is only the part of the problem you can see, and that fact governs everything about how it has to be repaired. The spalling on the surface, the cracked, flaking concrete and the exposed reinforcement, is the end result of corrosion that has been progressing inside the concrete, and the corrosion usually extends beyond the area that has visibly broken away. A repair that only addresses the concrete that has already spalled, without dealing with the corroding steel and the concrete around it that is on its way to spalling, is a repair that fails, because the corrosion it left behind keeps going and the damage reappears alongside the patch. A patch is not a repair. A durable spalling repair is a considered piece of work rather than a cosmetic fill.
Doing it properly means removing the affected concrete back to sound material and beyond the visibly damaged area, treating or replacing the corroded reinforcement, and reinstating the concrete with a material and a method that restore the protection the steel needs and bond properly to the existing structure. It also means addressing why the corrosion started, because concrete does not spall for no reason, and if the cause, usually moisture and salt reaching the steel, is not addressed, the repair is working against the same force that caused the original damage. A repair that ignores the cause is a repair with a limited life.
Why the cause has to be dealt with too
The most common reason a spalling repair fails prematurely is that it treated the symptom and left the cause running. Concrete spalling begins when moisture and salt reach the reinforcement, so a lasting repair has to consider where that moisture and salt are coming from and reduce it: improving drainage so water is not sitting against the concrete, addressing a leak that is keeping an element wet, and in the coastal environment recognising that salt-laden air is a constant that the repair material and the protection have to be chosen to resist. Where the element is exposed to the weather and the coast, the repair specification has to account for that ongoing exposure, or the new concrete will begin the same journey the old concrete took.
This is why proper spalling repair, particularly on structural elements or in coastal conditions, is specialist work rather than a job for a general patch. Getting the diagnosis right, how far the corrosion extends, what is driving it, what the element is carrying, and getting the repair specification right, the extent of removal, the treatment of the steel, the reinstatement material, the protection against future ingress, is what separates a repair that lasts from one that spalls again in a few years. On a structural element the stakes are higher still, because the repair has to restore not just the appearance but the load-carrying capacity of the concrete, which is an engineering question.
What it means for a buyer or owner
For a buyer, evidence of concrete spalling, or of a previous spalling repair, is worth understanding rather than glossing over. Active spalling on a structural element is a major defect that will need proper, and potentially expensive, repair, and it is worth knowing the extent before committing. A previous repair is worth a closer look too, because a cosmetic patch that did not address the corrosion or the cause may be hiding continuing deterioration rather than resolving it, and spalling that reappears alongside an old repair is a sign the earlier work was inadequate. In a coastal apartment or multi-storey building, where structural concrete spalling can become a major shared repair, the question extends to the building's records and whether a remediation program is anticipated or under way.
For an owner who has spalling, the practical message is not to reach for a quick patch. Getting the extent and cause properly assessed, and the repair properly specified and carried out, is more expensive up front than a fill, but it is the difference between fixing the problem and painting over a process that continues underneath. Where the spalling affects structural elements, a structural engineer or a concrete-repair specialist is the right starting point, because the diagnosis and specification are beyond what a cosmetic repair can address. Getting them wrong means paying twice.
Common questions
Can you just patch concrete spalling?
No. The steel keeps rusting behind a patch, which is pushed off within years, and patching can accelerate corrosion in adjacent concrete. Proper repair arrests the corrosion and restores cover.
Who repairs concrete cancer?
A structural engineer assesses and designs the remediation under AS 3600; a concrete remediation specialist or registered building contractor carries it out. In WA, building work over $20,000 needs a registered builder.
What standard governs concrete repair?
AS 3600, the concrete structures standard, which sets durability and minimum cover by exposure classification and is the deemed-to-satisfy reference for concrete under the National Construction Code.
This comes up on every apartment & strata inspection we carry out.
Read next: the name on the sign may not be the business building your house and concrete spalling: when the steel inside rusts.
Sources
Read rather than recalled. Summarised here; the documents themselves are Crown copyright and are linked rather than reproduced.