Understanding Powder Coating Primers and Their Applications
While primers are not required for all projects, they can serve as a foundation for subsequent topcoats by providing improved adhesion and corrosion resistance. Available in two primary chemistries, epoxy and hybrid, primers offer unique benefits tailored to specific application needs. In this article, we'll delve into the characteristics, advantages, and types of primers with their end use cases, helping you make informed decisions for your powder coating projects.
Although similar in nature, there are some differences between an epoxy and a hybrid primer. Epoxy primers generally have high mechanical strength and corrosion resistance. Hybrid primers are epoxy-modified polyester that add over-bake stability and improve adhesion properties to epoxies.
Unless otherwise stated, primers must be partially cured prior to applying the top coat. This ensures seamless inter-coat adhesion between the primer and the topcoat. For a partial cure, we recommend 50% to 80% of the specified powder’s cure schedule, while also considering the time it takes for the metal to reach the curing temperature (PMT). For instance, Zinc Rich Primer’s full cure schedule is 15 min @ 375ºF. So, you would bring the part up to 375ºF, and then cure for 7-12 min. Out-Gass Builder primer is one exception to this rule. This powder is unique and requires a full cure cycle. Fully curing primers that are not specifically designed for this purpose will result in a more challenging application process of the topcoat and diminished field durability.
Several advantages of utilizing primers in your project include:
- Extending the longevity of the coating in exterior environments.
- Adding a second layer to the substrate to add resistance against impact.
- Helps reduce orange peel to ensure a uniform topcoat application.
- Assists in addressing coating issues such as outgassing.
- Providing additional protection to prevent the metal from corrosion.
Epoxy Primer
A reliable, epoxy based coating that provides a durable and long lasting finish. It's versatile and can be applied to various substrates. This primer excels in protecting surfaces from corrosion and chemicals.
Key Features:
- Includes White Epoxy Primer and Gray Epoxy Primer
- Suitable for use on steel and aluminum
- Increases overall chemical resistance
- Use White Epoxy Primer to help preserve top coat brightness
Zinc Rich Primer
An epoxy coating enriched with zinc serves as a rust resistant barrier. The zinc within the coating reacts with oxygen to produce zinc oxide, which effectively shields a steel substrate from corrosion. Conversely, zinc oxide in contact with aluminum initiates corrosion, thereby diminishing the coating’s lifespan.
Key Features:
- Available at a higher concentration (Heavy Zinc Primer) for environments with higher corrosion rate
- Increases durability and impact resistance
- Not suitable for use on aluminum
Red Primer
A good primer for applications that require a lower temperature. This powder is best utilized for substrates that cannot be cured at the typical 400°F.
Key Features:
- Suitable for use on steel and aluminum
- Good choice for parts that require a low cure temperature
Out-Gass Builder Primer
Out Gass Builder Primer has two primary functions: reducing/eliminating outgassing on porous metals and smoothing out imperfections on damaged substrates. Its high-build characteristics enable it to be used as a building/filling material, like a “Bondo” for powder coating. It can be applied, cured, and sanded in multiple layers to achieve a smooth finish.
Key Features:
- Designed to address outgassing issues for cast metals and aluminum
- Can be used as a building/filling material
- Can be sanded and recoated