Concrete cancer is one of the most common structural issues affecting buildings across Sydney and coastal NSW. Despite its name, it is not a disease but a progressive deterioration process that, if left untreated, can compromise the structural integrity of balconies, car parks, facades and other concrete elements.
What causes concrete cancer?
Concrete cancer occurs when steel reinforcement inside concrete begins to corrode. As the steel rusts, it expands to several times its original volume, cracking and displacing the surrounding concrete. This process is typically triggered by carbonation of the concrete cover or chloride ingress from coastal environments.
In Sydney, the combination of salt-laden air, humidity and aging building stock from the 1960s through 1980s makes concrete cancer particularly prevalent. Buildings within a few kilometres of the coastline are especially vulnerable.
How to identify concrete cancer
The most visible sign is spalling, where sections of concrete crack, bubble or fall away from the surface, often exposing rusted reinforcement underneath. Other indicators include rust staining on concrete surfaces, hairline cracking in regular patterns, and hollow-sounding areas when tapped.
Early detection is critical. What begins as minor surface cracking can progress to significant structural damage if left unaddressed. Regular building condition assessments by a qualified structural engineer are the most reliable way to identify concrete cancer before it escalates.
The concrete cancer repair process
Professional concrete cancer repair follows a methodical sequence defined by the structural engineer in a repair methodology or specification. The process typically involves the following stages:
Breakout and preparation: Damaged concrete is removed using controlled mechanical methods to expose the corroded reinforcement. The breakout area extends beyond the visible damage to reach sound concrete and uncorroded steel.
Steel treatment: Exposed reinforcement is cleaned to remove all corrosion products, typically to a bright metal finish. A passivating primer or protective coating is then applied to the steel to inhibit future corrosion.
Repair mortar application: A polymer-modified repair mortar is applied in layers to reinstate the concrete profile. Product selection, mixing ratios and application thickness are all specified by the engineer.
Protective coating: An anti-carbonation coating or waterproof membrane is applied over the repaired area and surrounding concrete to prevent future moisture and CO2 ingress.
Why documentation matters
Every stage of concrete cancer repair should be recorded in an Inspection and Test Plan (ITP). This document provides traceable evidence that the work was completed in accordance with the engineer's specification, the correct materials were used, and each stage was inspected before proceeding.
An ITP supports the builder's quality obligations, satisfies the engineer's review requirements, and provides a clear record for the building owner. Without proper documentation, there is no verifiable evidence that the repair was executed correctly.
Choosing the right repair contractor
Concrete cancer repair is not general concreting work. It requires technical understanding of corrosion mechanisms, familiarity with repair material systems, and the ability to execute to an engineer's repair methodology. When selecting a subcontractor, builders should look for demonstrated experience with remedial concrete works, a clear quality assurance process, and the ability to deliver ITP documentation with every project.