People often come to us with a colour in mind and very little else decided. That is fine as a starting point, but the colour is the last thing that matters technically. What matters first is where the part lives, what it has to survive, and what substrate it is made from. Everything else follows from those three answers.

Start Here: Three Questions to Answer First

Question 1: Will this part ever be exposed to direct sunlight?

This is the most important question in any outdoor powder coating specification. UV radiation breaks down epoxy linkages in the coating over time, causing chalking and colour fading. If the part will sit outdoors, even occasionally, epoxy-containing coatings are the wrong choice.

Yes, outdoorsPure polyester chemistry only. UV resistance is the non-negotiable requirement here and only polyester delivers it consistently.

No, indoors onlyHybrid epoxy polyester is a good option. You get better corrosion and chemical resistance at a lower cost than polyester.

Question 2: What is the substrate?

Steel and aluminium need different pre-treatment and respond differently to coating chemistry. Galvanised steel, cast iron, and MDF each have their own requirements too.

SteelZinc phosphate pre-treatment. Hybrid or polyester depending on the environment. Higher film build on edges and complex geometry.

AluminiumChromate-free conversion coating. Pure polyester for anything outdoors. Qualicoat specification for architectural applications.

Question 3: What does the coating need to resist?

UV and weather are not the only threats. Chemical exposure, impact, temperature cycling, and moisture all influence which chemistry is right.

Corrosion and chemicalsHybrid epoxy polyester for indoor steel. Higher film build. Zinc phosphate pre-treatment is essential.

Impact and abrasionPolyester with higher film build (80 microns plus). Consider textured finishes which hide minor surface damage better than gloss.

The Main Chemistries and When to Use Them

Epoxy Polyester Hybrid

Indoor / Corrosion protection

Use for

Electrical enclosures and switchgear
Industrial shelving and racking
Indoor machinery and equipment
Automotive underbody components
Pipework and internal surfaces

Do not use for

Anything exposed to sunlight
Architectural aluminium
Outdoor gates, fencing, furniture
Any application where colour stability over years is required

Pure Polyester (TGIC or HAA)

Outdoor / UV resistance

Use for

All outdoor steel applications
Architectural aluminium (Qualicoat Class 1)
Agricultural and construction equipment
Outdoor furniture and street furniture
Automotive exterior trim and wheels

Worth knowing

TGIC-free (HAA hardener) versions available for REACH compliance
Slightly more overbake-tolerant than hybrids
Works on both steel and aluminium substrates
Wider colour range than super-durable options

Super-Durable Polyester

Demanding outdoor / Long service life

Use for

High UV environments: Middle East, Mediterranean, tropical
Qualicoat Class 2 architectural specifications
Buildings and facades with 15 to 25 year service life requirements
Prestige projects where colour retention matters over decades

Worth knowing

15 to 30% higher material cost than standard polyester
Smaller approved colour range
Requires Qualicoat-licensed applicator for certified work
Payback is in avoided remediation cost on long-life structures

Polyurethane Powder

Premium finish quality

Use for

Applications demanding exceptional surface smoothness
Automotive interior trim and visible components
High-gloss decorative applications
Parts where flow and levelling are critical

Worth knowing

Higher cost than polyester systems
Sensitive to moisture during application
Excellent hardness and scratch resistance
Not always necessary when a well-specified polyester achieves the same result

Film Build: The Variable Nobody Talks About Enough

Chemistry gets most of the attention in coating specifications. Film build gets less than it deserves. A pure polyester coating applied at 45 microns will not perform anything like the same chemistry at 75 microns, especially on corrosion protection and impact resistance.

For most industrial applications, target 60 to 80 microns mean film build. On parts with complex geometry or tight inside corners, check that edges and recesses are hitting at least 40 microns. That is where coating fails first and where pre-treatment problems show up earliest.

Application Type	Recommended Film Build	Reason
General industrial steel (indoor)	60 to 80 microns	Standard corrosion and mechanical protection
Outdoor steel (gates, railings, equipment)	70 to 90 microns	Additional barrier against moisture ingress
Architectural aluminium (Qualicoat)	60 microns minimum mean, 40 minimum at any point	Qualicoat Specification requirement
Electrical enclosures (dielectric requirement)	80 to 120 microns	Dielectric strength increases with film build
Automotive underbody	80 to 100 microns	Stone chip and moisture resistance

When You Are Not Sure

If your application does not fit neatly into one of the categories above, the safe approach is to describe the service environment to your coater and ask them to recommend a chemistry and test standard. A reputable applicator should be able to point you to an accelerated weathering test result or salt spray data for the powder they are recommending.

If they cannot, that is worth knowing before you place the order.

Factory Story

We had an enquiry from a fabricator making outdoor advertising structures. They had been using a hybrid epoxy polyester because their previous coater had told them it was "more durable." Technically, that is true in some dimensions. But eighteen months into installation, the boards were chalking badly in the sun, and the client was fielding complaints from the end customer. When they came to us, the first thing we asked was whether the structures were outdoors and in direct sun. They were, all of them. We switched them to a pure polyester with a 75-micron target film build. The structures have now been up for over two years without any visible change in appearance. The previous coater was not wrong about the chemistry being durable. They were wrong about which kind of durability mattered.

Not sure which coating type is right for your parts? Give us a description of the substrate, the environment it will operate in, and any test standards you need to meet. Our technical team will come back to you with a recommendation and the data to support it.

What's the Best Type of Powder Coating for My Project?

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