Understanding concrete spalling
Concrete cancer is caused when the steel reinforcing within a concrete slab begins to rust. As the steel rusts it expands, displacing the concrete around it, causing it to become brittle and crack thus accelerating the process.
Signs of concrete cancer include:
- Crazing and cracking concrete (concrete spalling)
- Rust stains which seem to leak out from within the concrete
- Bubbling (also called Plating) of concrete render
- Leaks which appear in overhead concrete surfaces
The dangers of concrete spalling
Concrete spalling – especially on the outside of a building – not only looks terrible, but it is potentially dangerous too. Over time, and with increased exposure to the elements, untreated pieces of concrete may fall from your structure. The risk is it falling and damaging property, or even worse, hitting a person walking below.
The causes of concrete cancer
There are a number of reasons your building may have spalling concrete. The more common reasons include:
- A poorly poured substrate which has allowed moisture to seep into it through cracks and voids
- Inadequate preparation of the reinforcing steel when the original concrete was poured.
- The ends of the reinforcing are too close to the surface. In heavy rains, water may seep through causing lime and other chemicals in the steel to oxidise.
- Incompatible metals being used in close proximity to each other, thus causing a reaction which allows water into the slab
- Stress fractures from bearing weight or general wear-and-tear allow water to penetrate the concrete and react with the steel