Powder Coating Primers: When Do You Need One and Which Type Should You Use?
Choosing the correct powder coating is important, but for some applications the coating system can also benefit from a suitable powder coating primer.
Thermaset’s ThermaPrime range includes epoxy and epoxy-polyester powder coating primers developed for different requirements, including barrier protection, improved corrosion protection, anti-gassing properties and improved edge protection.
The correct choice depends on the substrate, application and performance required from the complete coating system.
What Is a Powder Coating Primer?
A powder coating primer is applied to the prepared substrate before the final powder coating topcoat.
Thermaset manufactures the ThermaPrime range of powder coating primers, designed to provide hard, durable and protective finishes for a variety of specialist applications.
Different ThermaPrime products have been developed for different requirements, so selecting the correct primer is important.
Does Powder Coating Always Need a Primer?
No. Not every powder coating application requires a primer.
Whether a primer is required depends on factors including the substrate, pretreatment, coating system, service environment and required lifespan.
A suitable primer can improve properties including corrosion protection, adhesion, edge coverage and resistance to outgassing.
Where a primer is required, it should be selected as part of the complete coating system rather than considered separately from the topcoat.
ThermaPrime PBP 110 – Epoxy Barrier Primer
ThermaPrime PBP 110 is an epoxy powder coating barrier primer.
It is designed for interior use or for use as a primer or barrier coating and is formulated using selected epoxy resins and pigments.
Thermaset describes PBP 110 as providing a tough decorative finish on difficult substrates with excellent outgassing and overcoating properties.
PBP 110 itself is not suitable for exterior exposure. For exterior applications, Thermaset specifies that it should be overcoated with a suitable exterior-grade coating, such as an architectural-grade polyester powder coating.
ThermaPrime PPC 120 – Anticorrosive Powder Coating Primer
ThermaPrime PPC 120 is a zinc-free epoxy-polyester powder coating primer designed to provide improved corrosion protection for mild steel.
It contains advanced anticorrosive pigments which have a passivating effect on the steel substrate.
Thermaset states that if penetrating damage occurs to the coating, the PPC 120 system will considerably limit the spread of corrosion.
Light grey is available as standard, with other colours available to manufacture to order.
ThermaPrime PZP 130 – Zinc Phosphate Powder Coating Primer
ThermaPrime PZP 130 is an epoxy powder coating primer containing zinc phosphate.
It has been developed to provide improved corrosion protection for mild steel.
Thermaset recommends PZP 130 for use as an anticorrosive primer where good-quality chemical conversion pretreatment would normally be recommended or specified but may not be available.
The primer is intended to be overcoated with a suitable Thermaset powder coating selected according to the end-use application.
Thermaset recommends that PZP 130 is partially cured before the topcoat is applied. The substrate must also be clean and free from rust, grease, oil and mill scale.
Trials are recommended to optimise application conditions before full-scale use.
ThermaPrime AGP 135 – Anti-Gassing Powder Coating Primer
Some substrates are prone to outgassing during the powder coating process.
ThermaPrime AGP 135 is an epoxy-polyester anti-gassing powder coating primer specifically formulated for problem substrates that are prone to outgassing.
Thermaset identifies examples including:
- Cast aluminium
- Steel
- Galvanised steel
- Zamak
AGP 135 should be fully cured before a topcoat is applied.
Thermaset specifies a minimum curing schedule of 10 minutes at 180°C peak metal temperature and recommends a minimum film thickness of 60 microns to achieve good protection.
ThermaPrime EEP 140 – Extreme Edge Anticorrosive Primer
ThermaPrime EEP 140 is a zinc-free epoxy-polyester powder coating primer designed to provide improved corrosion protection for mild steel.
It contains advanced anticorrosive pigments with a passivating effect on the steel substrate.
One of its important characteristics is its modified viscosity profile.
Thermaset states that this produces improved edge coverage and therefore improved edge anticorrosion protection compared with other primers in the ThermaPrime range.
EEP 140 can be applied by manual or automatic spray equipment, with a dry film thickness of 60–100 microns recommended for best performance. Thermaset specifies a minimum of 60 microns to achieve good protection.
Surface Preparation Is Important
Correct substrate preparation remains important when using a powder coating primer.
Thermaset’s technical information specifies that, for maximum adhesion, substrates should be thoroughly cleaned of grease, rust and other contamination.
Recommended preparation varies according to the primer and substrate and can include solvent or chemical degreasing, grit blasting and appropriate chemical pretreatment.
Where chemical pretreatments are used, Thermaset recommends following the advice of the pretreatment chemical supplier.
Which ThermaPrime Powder Coating Primer Should You Choose?
The ThermaPrime range provides different options according to the requirements of the application.
PBP 110 – Epoxy barrier primer for interior use or use as a primer/barrier coating.
PPC 120 – Zinc-free epoxy-polyester primer designed for improved corrosion protection of mild steel.
PZP 130 – Zinc phosphate epoxy primer developed for improved corrosion protection of mild steel.
AGP 135 – Epoxy-polyester anti-gassing primer for substrates prone to outgassing.
EEP 140 – Zinc-free epoxy-polyester primer developed for improved corrosion protection and improved edge coverage.
The appropriate primer should be selected according to the substrate, environment, pretreatment and topcoat requirements.
Thermaset ThermaPrime Powder Coating Primers
Thermaset manufactures the ThermaPrime range of specialist powder coating primers for commercial and industrial applications.
Technical Data Sheets are available for individual ThermaPrime products, providing information including preparation, application, curing conditions, film thickness and performance testing.
If you’re unsure which primer is suitable for your application, contact Thermaset for technical support.
Frequently Asked Questions
Does every powder coating application need a primer?
No. The requirement depends on factors including the substrate, pretreatment, coating system, service environment and required lifespan.
Which Thermaset primer is designed for outgassing?
ThermaPrime AGP 135 is an epoxy-polyester anti-gassing primer formulated for problem substrates prone to outgassing.
Does Thermaset manufacture a zinc phosphate powder coating primer?
Yes. ThermaPrime PZP 130 is an epoxy powder coating primer containing zinc phosphate and is designed to improve corrosion protection on mild steel.
Which Thermaset primer is designed to improve edge protection?
ThermaPrime EEP 140 has a modified viscosity profile designed to provide improved edge coverage and improved edge anticorrosion protection.
Where can I find technical information for ThermaPrime products?
Technical Data Sheets for Thermaset’s ThermaPrime products are available through our website or by contacting our team.
