Another name for this issue, is concrete spalling.
How Does It Start?
Concrete cancer begins when the steel mesh, wires, or rebars that may reinforce concrete are exposed to moisture. When the lime in the concrete gets wet, a chemical reaction causes the steel to rust. The corroded steel expands, triggering fractures. These cracks allow more water to enter, and they may lead, perhaps, to the facade of a home or building crumbling off. Concrete cancer on horizontal surfaces such as roofs leads to leaks.
What Are the Effects?
When signs of concrete cancer appear, the deterioration has been underway for about five to 15 years. Signs of concrete cancer are sometimes difficult to detect unless a person who is an expert in this structural defect, like those from Jeffrey Hills and Associates, examines a home. In addition to cracking, crumbling and leaky roofs, indicators of spalling include rust stains that seep through the concrete, bubbles forming on the render of the concrete, and cracks with white flakes on the surface. Due to age and home building techniques, homes build before 1990 are more susceptible to these effects.
What Can You Do?
To address the problem, seal cracks. For larger areas, you may want to break the concrete and remove the corroded steel. Then, you can either replace the good steel or treat it with anti-corrosives. On the concrete surface, you should then get repair mortars to be used. Unless you know how to do this already, this is probably something that you can leave up to a professional. Finally, the concrete is protected by elastomeric membranes that are waterproof. They can be either sprayed or rolled on, and they are used on flat roofs too.
How to Prevent This from Happening
To prevent spalling, protect concrete against moisture. Seal cracks. Buildings near salt water where its chlorides can enter the cement and cause concrete cancer must be protected. Special paints are available that protect against the corrosive chemical effects of being situated in a seaside community. On a roof, standing water should be removed, and the cause of poor water runoff should be addressed.
When concrete cancer is suspected, property owners are advised to seek an evaluation from a professional who specializes in treating it. The entire structural integrity of the building is at stake. In extreme cases, this problem has necessitated the complete or partial demolition of a structure.