Can You Powder Coat Over Primer?

Powder coating helps metal surfaces retain their appearance and it protects them from corrosion and wear and tear. To ensure powder coating performs as well as possible, you must prepare metal surfaces carefully before applying it. 

Does this preparation include the use of primers? If so, what happens when you apply powder coating over primer?

Preparing Surfaces for Powder Coating

To maximise the effectiveness of powder coating, you must first prepare the surface you wish to apply it to.

This involves degreasing , etching and pre-treatment.

There are three ways to degrease metal surfaces:

• Vapour degreasing
• Aqueous washing 
• Immersion washing.

Vapour degreasing uses hot vapour from a heated chlorinated hydrocarbon solution to clean metal parts through condensation.

Aqueous washing cleans surfaces with detergent and hot water jets.

In immersion washing, the metal part passes through a series of tanks, applying a cleaning solution followed by hot and cold rinses.

After degreasing, the surface needs to be etched to remove any contaminants within the surface and then there are various pre-treatments to prepare metal surfaces for powder coating.

These include:

• Phosphating
• Chromating
• Non Chrome 

Chromating works by providing a conversion of the surface to create a barrier against corrosion, improving the eventual bonding process between the surface and the powder coating and is only suited to aluminium and zinc surfaces when preparing them for powder coating.

Phosphating works in a similar way but is suitable for Steel and Zinc surfaces 

At this stage, there is the potential to apply primer to surfaces to add extra protection to them from the effects of corrosion.

How Powder Coating Primers Work

Primers protect metals from corrosion. They are especially useful where surfaces will be exposed to moisture and wet in outdoor or aquatic environments.

Using a primer also improves the bond between the surface and the powder coating. Primers are usually zinc or epoxy-based. They act as airtight sealants. 

Aluminium and Zinc surfaces do not need Primers

For Mild Steel surfaces that are exposed to external conditions, Zinc or Zinc Free Primers should be used.

But both epoxy and zinc primers add a protective layer against corrosion, stopping it from creeping under the powder coating layer.

When Should You Powder Coat Over Primer?

Ultimately, you’ll need to base your decision on the specific job. Always consider the function and location of the metal part you’re powder coating.

The metals which may benefit from having a primer applied before powder coating are:

• Stainless and carbon steel
• Cast and wrought iron
• Zinc alloys
• Cast and wrought aluminium

However, you should also check first that the powder coating you wish to apply will work well with a primer.

For example, powder coatings with textured finishes must go directly onto the surface with no primer, otherwise, the primer base coat may prevent the powder from forming textures properly.

Answering Your Powder Coating Questions

For more information about powder coating and how, where and when to apply it, please contact us.