Let's Make Zinc-Rich Primers Simple (July 2022 Update)

Zinc-rich primers are an excellent form of corrosion protection for facility owners and paint contractors to consider. Let’s first address how zinc primers work to ensure a complete understanding of these coating systems.

zinc coating on marine surface

How do zinc-rich primers work?

Zinc-rich primers are part of a group of coatings known as galvanic protection systems. Galvanic systems are also know “sacrificial” systems because the coating used corrodes instead of the integral structure or component.

Zinc is more electrically active than steel and other structural materials. When the corrosion cell is formed (whenever the structure interacts with moisture, i.e., the electrolyte), the zinc primer acts as the sacrificial anode, protecting the structural material. Magnesium, aluminum and zinc can all be used as galvanic coating systems because they’re all active metals.

What are the advantages and disadvantages of zinc-rich primers?

Zinc-rich primers, and all galvanic systems, are perfect primers for steel assets in highly corrosive environments. Zinc is particularly useful in marine, tanker and underground applications, i.e., immersive environments. Any environment exposed to constant moisture will benefit from a zinc primer.

The main drawback of zinc primers is that they are consumed while providing protection. This means they have a relatively limited lifetime.

Types of zinc primers

Zinc primers come in two basic forms: inorganic and organic zinc-rich coatings.

Inorganic zinc vs. organic zinc coatings

Inorganic zinc coatings:

Can be used without a topcoat in mild atmospheric environments
Usually only use silicate as a binder
Contain more zinc and provide better galvanic protection
Require abrasive blasting or near-white blasting to be long-lasting and effective
Are usually applied in shops via a spray

Organic zinc coatings:

Must be top-coated to provide long-lasting protection
Use a wide variety of binders from epoxy to alkyd
Are easier to apply
Are usually applied in the field via a brush or roller

Organic zinc coatings usually act as maintenance coatings for inorganic coatings due to their relative ease of application.

Zinc chromate vs. zinc phosphate

In general, zinc chromate is a more effective and robust than zinc phosphate. Zinc chromate is epoxy based, while zinc phosphate is an alkyd, which means zinc chromate is more durable when used in a primer.

While zinc chromate primers might be more durable, longer lasting, and ultimately more effective, they also come with serious risks.

Studies have found that zinc chromate is harmful and carcinogenic to humans. The New Jersey Department of Health and Senior science notes there are no safe levels of carcinogens in humans.

If you choose to use zinc chromate, make sure to have proper ventilation and use the appropriate breathing equipment. Use zinc chromate primers at your own risk.