Corrosion (rust) is a process where chemical reactions take place through the exchange of electrons. The corrosion reactions that would otherwise naturally occur can be inhibited by preventing the exchange of electrons. Since there needs to be iron, water and free electrons present for rust to form, eliminating any one of these agents will prevent rust.

One rust prevention method is to insulate the metal from moisture and oxygen by covering it with a protective coating such as spray-on type rustproofing (rust proofing), undercoating or paint.

Another method is Capacitive Coupling, used by some products, which relies on the paint as a dielectric or barrier to the free electrons, causing the metal to be at a lower potential difference, theoretically slowing rust formation.

Cathodic Protection is another method used to prevent rust using one of two technologies; either Impressed Current or Sacrificial Anode. So, what are the limitations of Undercoatings (spray-on type rust proofing), Capacitive Coupling and Cathodic Protection?