What if the normal paint is used on steel while using steels in the structures instead of coating (e.g. epoxy coating)?

The normal paints which we use for painting walls or exterior metals for aesthetic purposes do not use for the painting of the interior metals i.e. steels which are used as structural rebars, tension carrying components of structure, for some specific reasons. Firstly, the normal paints make the steel surface too smooth that the steel can’t build well in contact with the concrete surface. Hence the phenomenon of pulling out the steel from the concrete can occur during the application or experiencing large loading. This leads to the opposite theoretical concept of the deformed bars which are introduced to increase the friction between the steel and the concrete. Besides the surface should be prepared for normal paint. Otherwise, the paint would be unsteady, some portion being unpainted. 

Pull out of Steel Due to Load

The coating type paint makes the surface of steel too micro-level rough exterior that it can build more friction with the surface of the concrete and makes the bond more strong between them against loads. Thus, it follows the concept of sing deformed bars instead of plain steel bars. Additionally, there is no need of surface preparation for coating. Some of the popular coatings are as follows:

• Epoxy Steel Coating
• Polyurethane Steel Coatings
• Zinc Coatings