Concrete Cancer Repair for Sydney Strata Buildings
We carry out concrete cancer repair in Sydney apartment buildings, scoped by testing rather than by what can be seen.
Rust stains running down a soffit. A hairline crack that has started to lift at one edge. A patch of render that sounds hollow when you tap it. By the time concrete cancer is visible from the ground it has usually been developing for years, and the question in front of a committee is no longer whether to act, but how far the repair has to go.
We repair concrete cancer in apartment buildings across Sydney, from a single balcony soffit to a full car park slab. The scope comes from testing rather than from what can be seen, because those two things are rarely the same size.
What concrete cancer actually is
Concrete cancer is corrosion of the steel reinforcement inside a concrete element. Steel sitting in sound concrete is protected by the alkalinity around it. When carbon dioxide works its way in from the surface, or chlorides reach the bar, that protection breaks down and the steel begins to rust. Rust takes up several times the volume of the steel it replaces, so it pushes the surrounding concrete outwards until it cracks and falls away.
That falling away is concrete spalling, and the two words describe one failure caught at different stages.
Three things drive it in Sydney buildings. Shallow cover from the original pour, water getting in through a failed membrane or a blocked drain, and airborne chlorides in the suburbs close to the water. Most of the buildings we survey have two of the three.
Testing before quoting
A visual inspection tells you where the concrete has already failed. It tells you very little about how much more is about to. Before pricing a repair we survey the element properly:
Test 01
Delamination survey
By hammer tap or acoustic testing, to find concrete that has debonded but not yet fallen.
Test 02
Cover meter reading
To establish how much protection the reinforcement actually has.
Test 03
Carbonation depth testing
On cored samples, to see how far the front has travelled.
Test 04
Chloride sampling
Where the building sits close to the water.
That survey is the difference between a repair that holds and one that fails at the patch edges within two years. Patching what is visible without measuring what sits behind it is the most common reason a building pays for the same work twice.
How the repair is carried out
Once the extent is known, the sequence is consistent.
1
Break out to sound concrete
We break out to sound concrete, past the corroded zone rather than to the edge of the visible damage.
2
Clean and treat the reinforcement
Exposed reinforcement is cleaned back to bright steel and treated, and where a bar has lost section it is supplemented or replaced.
3
Galvanic anodes where chlorides call for them
Where chloride levels make further corrosion likely, galvanic anodes go in and corrode sacrificially so the reinforcement does not.
4
Reinstate with a matched repair mortar
Reinstatement uses a repair mortar matched to the parent concrete for strength and shrinkage, not a general purpose product off a shelf.
5
Protect the finished surface
The finished surface is then protected, usually with an anti-carbonation coating. That last step is the one most often missing from a cheap quote, and it is the one that decides how long the repair lasts.
Repairs in an occupied building
Almost every building we work in is occupied. Residents stay in place, the car park stays in use, and reaching a balcony soffit means working past somebody’s home.
We sequence the program so the building stays livable. Containment and dust extraction on breakout, staged access so no resident loses their balcony for the whole job, and a schedule a strata manager can put into a notice without fielding twenty questions afterwards. Work in occupied buildings is most of what we do rather than an exception we accommodate.
Compliance, warranties and who signs what
Structural concrete repair to a Class 2 building sits inside the Design and Building Practitioners Act. That means regulated designs prepared by registered design practitioners, and a building compliance declaration lodged at completion. We lodge that declaration ourselves, because it cannot be delegated, and we sequence the design and the lodgement so they do not hold up an occupation certificate. What the Act asks of an owners corporation is set out on our Class 2 compliance page.
The work carries statutory warranties under the Home Building Act: six years on major defects, waterproofing included, and two years on everything else, from completion.
6 years
On major defects, waterproofing included, from completion.
2 years
On everything else, from completion.
Class 2 Builder Sydney is the trading name of Sydney Building & Construction Group Pty Ltd, Licence No. 283692C.
Have the extent tested
Send through photographs and we will tell you whether the element needs a survey. If it does, we will scope it, price it, and set out what the repair involves before anyone commits to a program. A site inspection is the quickest way to find out how big the job actually is.
