There are many causes of bearing steel from corrosion. As lack of protective concrete, concrete quality is poor, or is in the process of seawater corrosion, etc. As steel rust occupies very much larger volume (more than 10 times) than steel, the surrounding concrete cracks and tends to get separated from steel and finally it falls down. This is particularly important in the ceiling plaster under leaking roofs. If we notice any disturbance in this plaster, it should be repaired as soon as possible. There are many cases in which the ceiling plaster has fallen down suddenly.
The repair for such cases is carried out as follows.
Hammer test the area for loose areas and remove all loose particles of mortar, concrete, rust, etc. from the spalled surface and clean it with a wire brush.
Apply one coat of polymer bonding agent (latex based) over the entire area of steel and concrete to be treated.
Apply polymer modified 1:3 cement mortar over the reinforcement and provide necessary cover. Addition of super plasticizer to reduce water and the incorporation of fibres will help to produce strong mortar. If the area is large, guniting with additive for quick setting can be used for better efficiency of the work.
Apply two coats of polymer modified active corrosion inhibitor to the remaining steel. If additional steel is required, tie the new steel to the old steel by binding wires. Two coats of chromate paint can also be a substitute.
Cure the concrete.
Apply a coat of water proofing slurry coating for protection against environment, if necessary.