Coating of concrete performed by applying liquid or semi-solid materials to a concrete surface. The concrete coating can be paints, cement-based topping, overlay, and epoxy aggregate system. The purpose of the concrete coating is to stop the ingress of water inside concrete. The prevention of water ingress will prevent the ingress of aggressive chemicals such as chloride and sulfate.
Chloride diffuses into concrete in solution. The ingress of chloride will adversely affect concrete durability. Chloride will cause steel corrosion. Corroded steel will expand and exert stresses on concrete which can cause concrete cracking and spalling. Also, the effective cross-section and tensile strength of steel will be reduced. The ingress of sulfate will affect concrete durability also. Sulfate will react with concrete causing destructive expansion.
The concrete coating should prevent the ingress of water. If the water gets behind the coating under unknown conditions. The water will be trapped between the coating and concrete surface. The vapour pressure of trapped water will reduce the adhesion of the coats to concrete surface, and the coating will start to peel off.
Moreover, the water will create a suitable environment for the growth of mould (fungal hyphae) on a concrete surface. The selected surface treatment should be impermeable to liquid water but permeable to water vapor. The discharging of water vapor is important to avoid the undesirable effects such as loss of coating adhesion and growth of mould on the concrete surface.