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Epoxy Primer

Reviewed by Raghvendra GopalCheckmark
Last updated: July 8, 2021

What Does Epoxy Primer Mean?

Epoxy primer refers to a sealer that has a non-porous finish. It is primarily recommended as the first base coat over bare steel. These base coats or epoxy primers can be used over fiberglass, plastic or the black iron phosphate coating as well.

Epoxy primers are used for a wide variety of materials due to their strong adhesion, good mechanical ability, and durable chemical resistance in wet and high-humidity environments. The ability of an epoxy primer to resist corrosion is related to its thickness; the thicker the epoxy primer layer, the better the protection.

This primer can also be used on cracks and dents. Its bonding capacity is excellent and it produces a good surface finish. Epoxy primers not only offer excellent adhesion to metals, but also serve as a proper base for extra undercoat products and top coats (paint). Epoxy primers are also commonly used to coat metal cans and containers, especially those used to hold acidic food, such as tomatoes.
Epoxy is made up of chains of carbon linked to other elements such as hydrogen, nitrogen or oxygen, which is why it can be classified as an organic compound. These carbon chains occur through a covalent bond, in which the elements share a pair of electrons.

The term epoxy is broad and can at times refer to the epoxide functional group, which is made up of carbon and oxygen atoms in chains. Considering the fact that functional groups are a determining factor for the main characteristics of a molecule during a chemical reaction, molecules that contain the epoxide functional group react chemically in order to create a rigid, yet flexible material.


Corrosionpedia Explains Epoxy Primer

Epoxy primer is a sealer that produces a good surface finish on applied top coats. A two-part epoxy primer contains zinc phosphate, which acts as a corrosion-inhibiting pigment. Epoxy primers can be used to waterproof materials that consequently protect the bare metal from oxidation. A dry, very clean surface is needed before applying epoxy primer. Two-part epoxy primer needs to be mixed thoroughly before applying.

The term epoxy refers also to the epoxy resins that usually appear after curing, curing being a term that refers to a chemical process in which a material hardens due to air, heat, or chemical additives exposure. Curing occurs with the help of a catalyst in epoxy, which works as a chemical additive that increases the rate of a chemical reaction. An exothermic reaction is the result, creating a cross-linkage in the polymer. This resulting cross-linkage proves to be responsible for the rigidity and strength seen in epoxy materials.

Since paints in the automobile and marine industries are very important for resisting corrosion (rusting), epoxy coatings are widely used as primers to improve the adhesion of the metal surface. Epoxy primers are also used in structural steel coatings for high-build thickness with the application of only one or two coats.

A two-part epoxy primer is known as a structural steel primer. It needs two components that are cured chemically through cross-linking. This two-part epoxy primer produces a film that is resistant to abrasion, chemicals and moisture. It is very suitable for use on properly prepared steel and concrete. This primer is also recommended for power plants, marine applications, water treatment plants and tank exteriors. Filler can be applied directly over epoxy primer and more epoxy applied over the filler to completely encase it in epoxy.

Epoxy also provides some build so it can be used exclusively without any other primer/surfacer.
Epoxy can be reduced 50% and used as a sealer before a base coat.

The degradation of epoxy coatings having various filler materials has been studied under natural and accelerated environmental conditions. ZnO-containing epoxy coatings show more pronounced UV stabilization characteristics, which could extend the service life of the epoxy coating compared to other filler materials exposed to same environmental conditions. The relatively minor decrease in the adhesion strength by ZnO-containing coatings indicated its better mechanical integrity and UV resistant characteristics compared to coatings containing TiO2, Fe2O3 and graphite filler materials. The addition of antioxidants and photo-stabilizers in the epoxy coatings shows excellent resistance during aggressive salt spray tests with a negligibly minor loss in the adhesion strength without any blistering.


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