In corrosion protection, what is the effect of applying primer over existing paint?

Applying primer over existing paint is generally not recommended due to a few reasons related to the chemistry and adhesion qualities of the materials involved. Primer is designed to bond directly with the substrate or the bare metal surface to provide a strong foundation for subsequent layers of paint. When primer is applied over an existing paint layer, it may not achieve the proper adhesion required for effective corrosion protection and durability.

The existing paint can potentially interfere with the primer’s ability to cling adequately to the surface. This lack of proper adhesion could lead to issues like peeling or flaking in the future, undermining the protective qualities of both the primer and the outer paint layers. In addition, if the existing paint is not compatible with the primer (for example, if it is an oil-based paint and you use a water-based primer), it can lead to chemical reactions that degrade the integrity of the coating.

Overall, using primer directly on a properly prepped and clean surface is vital for achieving the best performance in terms of corrosion prevention and surface durability.