If you want a lifetime job, it could be painting the Sydney Harbour Bridge – once you finish you probably have to start at the other end again. The painting continues in order to stop the steel from corroding, and steel corrosion is what causes concrete rot, otherwise called concrete cancer or spalling.
How does concrete 'rot'?
Concrete is used in most commercial and residential buildings in a host of applications such as slabs, stairways, post and columns, support beams, balconies and verandahs, walls, pathways and pools. Huge volumes of concrete are involved in structures like bridges, wharves and high-rise towers. The concrete is generally reinforced using steel bars or mesh and in the larger developments significant amounts of steel are required for added strength.
The enemies of reinforced concrete are water and air. If these elements gain access to the steel enclosed within the concrete it can corrode – the steel expands as it breaks down and fractures the surrounding concrete. As the concrete cracks and crumbles, there is even greater opportunity for water and air to contact the reinforcing steel and the process intensifies. There are obvious safety issues as the structural integrity of the concrete is reduced.
How to identify concrete rot
It can be happening unseen within the concrete but as it continues it becomes more evident. You may notice rust marks running down the concrete, or the concrete flaking, cracking or crumbling. In extreme cases, large sections of the concrete will fall away, exposing the rusted reinforcing steel. Remedial treatment can involve substantial and expensive corrective measures.
A professional building inspection can identify the problem or warn of potential for future trouble. It can be water pooling somewhere, small cracks in the concrete or reinforcing too close to the concrete surface. Prevention is certainly better than cure with concrete rot – it may simply be a matter of improving drainage, painting a surface or sealing cracks with some sort of mortar or epoxy filler. If you have any concerns about concrete rot, it pays to get some expert advice.
I do like to be beside the seaside
Well yes, most of us do but it's here that concrete rot can be even more prevalent as chlorides in the moist, salty air react more aggressively with the reinforcing steel. Concrete rot is an ever-present issue in locations close to the sea and property owners need to be constantly on the lookout for any signs of deterioration and to ensure that protective measures are maintained.
The same can be said for chlorides associated with swimming-pool chlorine or saltwater pools.
Also, there is often moisture close to the ground surface in beachfront blocks and water can soak up into the structure. Large buildings with basement or underground car parks can experience the same problem with groundwater seepage.
In summary, concrete rot is a common problem. It can lead to significant structural damage which may be difficult and expensive to repair. It is not always easy to detect, it can result in serious safety implications and it can be avoided by getting expert advice and using the right materials and appropriate construction guidelines.