Powder Coating Galvanised Steel: Preparation, Outgassing and Choosing the Right Powder
Galvanised steel can be powder coated, but the preparation and coating system need to be carefully considered.
Thermaset’s technical guidance specifies particular pretreatment requirements for galvanised steel and also highlights the potential need for degassing or anti-bubbling measures depending on the type of galvanising.
Thermaset also manufactures specialist powder coating primers for substrates prone to outgassing, including galvanised steel.
Can Galvanised Steel Be Powder Coated?
Yes.
Thermaset includes galvanised steel within its substrate-preparation guidance across a number of powder coating ranges.
The important consideration is that the substrate must receive the appropriate preparation and pretreatment before the powder coating is applied.
What Pretreatment Does Galvanised Steel Require?
Thermaset’s technical guidance states that galvanised steel requires multistage pretreatment with either zinc phosphate or chromate conversion.
Depending on the type of galvanising, degassing or the use of anti-bubbling additives may also be required.
Thermaset recommends seeking detailed advice from the pretreatment supplier.
This means the preparation process should be established according to the actual substrate and coating requirements rather than treating every galvanised component in exactly the same way.
Why Is Degassing Important?
Thermaset identifies galvanised steel as one of the substrates where degassing or anti-bubbling measures may be required.
The company’s ThermaPrime AGP 135 is specifically formulated for problem substrates that are prone to outgassing.
Substrates listed by Thermaset include:
- Cast aluminium
- Steel
- Galvanised steel
- Zamak
If galvanised steel is being used, the possibility of outgassing should therefore be considered when establishing the preparation and coating process.
What Is ThermaPrime AGP 135?
ThermaPrime AGP 135 is an epoxy-polyester anti-gassing powder coating primer.
It is formulated for use on substrates prone to outgassing and specifically includes galvanised steel among its listed applications.
Thermaset specifies that AGP 135 should be fully cured before applying a topcoat.
The minimum specified curing schedule is 10 minutes at 180°C peak metal temperature.
AGP 135 should be applied by corona electrostatic spray equipment with an even dry film thickness of 60–80 microns. Thermaset recommends a minimum of 60 microns to achieve good protection.
Preparation Before Applying AGP 135
Correct preparation remains important when using an anti-gassing primer.
Thermaset provides specific preparation guidance for different substrates and recommends following advice from the pretreatment chemical supplier where chemical pretreatments are used.
The appropriate preparation should therefore be established before the primer and topcoat system is applied.
Choosing a Powder Coating for Exterior Galvanised Steel
Where a finished component will be used outside, the topcoat itself needs to be suitable for exterior exposure.
Thermaset manufactures polyester powder coatings designed for both interior and exterior applications.
Its polyester range is formulated to provide a tough decorative finish with excellent outdoor durability and resistance to yellowing.
Thermaset’s technical information distinguishes this from its standard epoxy coatings, which are not designed for long-term exterior exposure.
The intended environment should therefore be considered when selecting the final powder coating.
Colour and Finish Options
Once the appropriate coating technology has been established, the required colour and finish can be considered.
Thermaset’s polyester powder coatings can be matched to customer-supplied samples or many RAL and BS colour references.
Gloss, semi-gloss and matt finishes are available within its standard polyester powder coating range.
This allows the coating technology to be selected according to the performance requirements before the required appearance is specified.
Follow the Correct Curing Specification
Curing requirements vary according to the particular Thermaset powder coating product.
Thermaset advises customers to refer to the product box label for the recommended curing conditions.
Where a specification refers to peak metal temperature, the component itself needs to achieve the specified temperature.
A typical value for a number of Thermaset polyester powders is 10 minutes at 180°C peak metal temperature, but the specification for the individual product should always be followed.
Consider the Complete Coating System
Thermaset’s published technical information makes clear that substrate preparation, pretreatment, primer where required, topcoat and curing conditions all need to be considered.
For galvanised steel in particular, the technical guidance highlights:
- Appropriate multistage pretreatment
- The possible need for degassing
- The possible use of anti-bubbling measures
- Specialist anti-gassing primer options
- Correct curing of the selected product
The precise process depends on the substrate and the coating system being used.
Powder Coatings for Galvanised Steel from Thermaset
Thermaset manufactures an extensive range of powder coatings and specialist primers for commercial and industrial applications.
Where outgassing is a concern, ThermaPrime AGP 135 is specifically formulated for problem substrates including galvanised steel.
For exterior applications, Thermaset also manufactures polyester powder coatings designed to provide excellent outdoor durability.
Contact Thermaset’s technical team if you need help selecting an appropriate powder coating or primer for a galvanised steel application.
Frequently Asked Questions
Can galvanised steel be powder coated?
Yes. Thermaset provides specific substrate-preparation guidance for galvanised steel across its powder coating ranges.
What pretreatment does Thermaset recommend for galvanised steel?
Thermaset states that galvanised steel requires multistage pretreatment with either zinc phosphate or chromate conversion. Detailed advice should be obtained from the pretreatment supplier.
Can galvanised steel suffer from outgassing?
Thermaset states that, depending on the type of galvanising, degassing or the use of anti-bubbling additives may be required.
Does Thermaset manufacture an anti-gassing primer for galvanised steel?
Yes. ThermaPrime AGP 135 is an epoxy-polyester anti-gassing primer formulated for substrates prone to outgassing, including galvanised steel.
Which Thermaset powder coating is suitable for exterior applications?
Thermaset manufactures polyester powder coatings designed for interior and exterior use with excellent outdoor durability. The specification for the individual product should always be checked. Contact our team for more information.
