Damaged or cracked areas of concrete or plaster must be removed. While doing this, care should be taken that the cracks are completely removed from the surface and a well-defined cavity is formed without affecting the good concrete or plaster. The size of the cut depends on the size, depth and extent of the repair. Before doing this, all structural load bearing members such as columns, beams and slabs should be supported, propped or isolated so that the load on these members is reduced or temporarily transferred to other good structural members. Care should also be taken during repair that weak members do not lose their strength further due to chipping and other removal procedures.
Rust should be completely removed from steel by gentle tapping, wire brushing and cleaning. The entire surface should be cleaned of dust and dirt by sand blasting or any other effective method and washed thoroughly. Excess water is drained from the cavity and all cracks and joints are thoroughly inspected and sealed with mortar and cured for 7 days.
The reinforcing bars are to be given a protective coating and the concrete surface is coated with a thin layer of cement grout before placing the patching material.
The cavities are then filled with good quality mortar or concrete as required. The repair material should be filled in layers approximately 10 mm thick. For columns, beams and slabs, grouting with ordinary cement concrete or polymer modified cement concrete is resorted to. The surface is properly cured for 7 days.
The surface is then allowed to dry and a finishing coat of mortar is applied in two coats. The surface is also treated for 7 days.
Cracks can also be repaired using ferrocement. This is done by peeling off the affected plastering and replastering the surface after positioning a sheet of steel wire mesh of the required size within the plaster.
Cracks can be plugged and sealed using cement grout or various brands of epoxy compounds available in the market.
It is important that due care is taken for the safety of residents and others during and around the repair.
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