Updated July 2024 by Andrew Mackintosh
‘Concrete cancer’ or concrete spalling are the terms given to a range of defects in steel-reinforced concrete that ultimately undermine its structural integrity. Traditionally it’s a condition associated with coastal properties where salt and moisture damages the protective membrane on concrete and seeps through this relatively porous material. It’s no longer just an issue of the coast. The instance of concrete cancer in Brisbane is growing and can be very, very costly.
Action Property Inspections is a specialist service for pre-purchase building inspections in Brisbane. We do not offer concrete inspections as a stand-alone service however, will inspect the state of concrete as part of our pre-purchase reporting.
When I do home inspections in Brisbane’s north east or the Redlands area, concrete spalling has always been top of my “check list” but the growing issue of pollution-related spalling means that it’s fast becoming a problem in the inner Brisbane suburbs too. In my experience, concrete cancer is among the most “covered up” problems in homes for sale. Some sellers aren’t ethical. Shocking, I know. Because concrete cancer is such a deal breaker for buyers, sellers go to great lengths to disguise the signs. When I’m doing a building inspection in Brisbane, not just on the coast, I check for newly rendered concrete slabs. It’s a big red flag that the seller has “applied a disguise” to the affected area in hope that the buyer won’t notice the money pit they’re buying.
The causes of concrete cancer
More often than not, moisture and air are leading factors in the development of concrete cancer. Moisture attacks the steel reinforcing and causes it to rust. Air reacts on a chemical level with the steel, causing rust (iron oxide). The rusted reinforcing can expand up to seven times its normal diameter inside the concrete. The concrete itself doesn’t have a great deal of flexibility so it accommodates the expansion in the only way it can: by cracking. This allows even more moisture and air to get into the concrete. Eventually, whole pieces of concrete may flake or crumble away. This is known as concrete spalling or concrete scaling. It can impact any concrete area of a home or townhouse, including the slab, stumps or driveway.
Coastal risks
Concrete in coastal areas is more susceptible to concrete spalling because of the higher salt content in the environment, which also accelerates rusting. It’s also a significant issue in humid climates or areas of high rainfall such as Brisbane.
Moisture can work its way into the concrete in a number of ways. Sometimes there isn’t enough of a margin left between the reinforcement and the edge or the surface of a slab. It can also be caused by poor workmanship or inferior waterproofing materials or techniques. Steel reinforcing materials need to have been properly treated before being incorporated into a slab. Cracking of the concrete also provides an easy pathway for water to get into the concrete and attack the steel reinforcing underneath. Concrete is comprised of water, cement, sand and aggregate (like gravel, for example). If the mix was wrong to start with, with too much sand, it’ll be susceptible to failure. If the wrong type of sand (eg. beach or river sand) was originally used, over time it can be a recipe for disaster. The composition of the slump (ie. too much or too little water), or overworking the concrete when it is laid can also contribute to the problem. Eventually, failures like this can take the form of concrete cancer. Unfortunately, it can take many years for concrete cancer to become really obvious, and by then the damage can be extensive.
City risks
The rising rate of concrete spalling in capital cities, including Brisbane, is likely attributable to atmospheric changes. Carbonisation (or carbonation) is where carbon dioxide causes a chemical reaction in concrete, converting calcium to calcium carbonate. This changes the pH level in the concrete which in turn, damages the steel re-enforcement. Similarly, chlorine, including low levels of chlorine in Brisbane’s water supply, creates a chemical reaction in the concrete which then corrodes the interior re-enforcement.
Problems caused by concrete cancer
Concrete cancer can be a very dangerous defect to have in a building. It is at its most dangerous when the concrete cancer undermines the structural integrity of a critical structural element, such as an elevated balcony or verandah, like those so popular in Brisbane’s ‘Old Queenslanders’ or trendy apartments (click here to learn more). At best, concrete cancer is unsightly. At its worst, concrete cancer can cause a structural collapse. Crumbling concrete can also be a hazard in other ways too, falling and damaging property or even injuring people. It can be a public liability nightmare.
If you’re selling your property, concrete cancer can also adversely affect the value of your home. It’s often discovered and documented when a prospective buyer commissions a property inspection report.
If you are buying a property, concrete cancer can seriously undermine the value of your investment and place your family’s lives at risk.
Repairs
In some instances, you can carry out concrete cancer repairs, but always consult an expert to be sure you know exactly what you’re dealing with. Any crumbled or spalled concrete must first be cleared away so that access can be gained to the steel reinforcing underneath. An assessment must them be made as to whether the steel should be replaced or whether it would be sufficient to treat it with a rust inhibitor or an anti-corrosive. Steps must be then taken to properly waterproof the area before fresh concrete can be laid, especially in Brisbane where high rainfall can be a problem. In other circumstances, different concrete repair techniques may be used.
The symptoms and signs of concrete cancer
Take a quick look around a property and you might stumble across some signs of concrete cancer. The main symptom of concrete cancer is the crumbling or ‘spalling’ of the concrete.
However, concrete cancer can be hidden underneath paint or other building material such as tiles or brickwork. Here are just a few of the symptoms of concrete cancer:
- Distortion in the tiling or brickwork, and lifting of the tiles or bricks;
- Cracks in the concrete itself;
- Cracks in your ceiling or walls;
- Rust stains in concrete or rendered paintwork.
The risk for apartment buyers
High-rise apartments require regular sealant applications to protect the integrity of the concrete. If you’re buying into a body corporate managed apartment building, you may be legally obliged to pay for maintenance and repairs on the building’s concrete facade and any structural concrete. Do not purchase an apartment in a concrete building without getting a thorough building inspection and access to records around maintenance.
The challenge
Concrete cancer can be especially difficult to spot where there’s been a concerted effort to hide or disguise it. The only sure-fire way to distinguish between concrete cancer and something less worrying is to organize a professional pre-purchase building inspection. Get the advice of an expert to be sure of an accurate diagnosis. Action Inspections can assess the extent of your problem and give you advice about your concrete repair options so you can plan an appropriate and effective solution.