How to Select a Powder Coating: A Decision Guide

Choosing a powder coating comes down to four questions in a fixed order: where the part lives, what metal it is made of, what it has to survive, and what it has to look like. Get the order right and the choice is usually obvious. Get it wrong, most often by choosing on price before exposure, and the coating fails in months rather than years.

The short answer

Question 1, Where does the part live? (This decides more than anything else)

Ultraviolet exposure is the single most decisive variable, and it is binary in practice: either the part sees daylight or it does not.

Epoxy resin is excellent at almost everything except UV. Under sunlight the epoxy backbone breaks down at the surface and the film chalks: it goes dull, the colour washes out, and a wiped finger comes away with pigment powder on it. This is not a defect and it is not a manufacturing fault; it is the chemistry doing what epoxy chemistry does. It is also why an epoxy or epoxy-hybrid coating used outdoors will look tired within a single Indian summer.

Polyester resin does not have this weakness. That is the entire reason Pure Polyester exists as a separate product at a higher price.

Edge cases worth naming

• Under a shed or canopy but outdoors: still counts as exterior. Diffuse UV and rain both reach it.
• Inside a factory with skylights: usually fine for a hybrid, but check whether the part sits in a direct sun patch.
• Coastal locations: you now have two problems, UV and chloride. Pure Polyester handles the UV; specify the corrosion requirement separately and expect to increase film thickness and upgrade pre-treatment.
• Buried, enclosed or inside a cabinet: UV is irrelevant. Choose on corrosion and chemical exposure instead, which usually points to Pure Epoxy.

Question 2, What is the substrate?

Pre-treatment matters more than the powder. A premium coating over an unwashed, rusty surface fails faster than a basic coating over correctly prepared metal. If you take one thing from this guide, take that.

Question 3. What does it have to survive?

Corrosion

Corrosion performance is measured by neutral salt spray to ASTM B117 / ISO 9227, reported in hours until rust creep exceeds a defined limit. Oracle's tested values, at 70–80 µm on zinc-phosphated panels:

A caution about salt spray hours. They are a comparative laboratory measure. They rank coatings against each other under one accelerated condition; they do not convert into years of service life, and a coating with double the hours does not last double the time in the field. Use them to compare options, not to predict a warranty.

Chemicals

For acids, alkalis and solvents, Pure Epoxy is the strongest performer. If you know the specific chemical, the concentration and the contact time, tell us, generic "chemical resistance" claims are close to meaningless without those three numbers.

Heat

Standard thermosetting powders are not high-temperature coatings. If the part runs continuously above roughly 120 °C, that is a separate specialist conversation before you choose from this range.

Impact and flexibility

Parts that get knocked, stacked, or formed after coating need flexibility as much as hardness. All four Oracle lines pass a 5 mm mandrel bend with no cracking and achieve ≥5 mm Erichsen cupping. Film thickness is the lever here: going too thick makes a film harder and more brittle, and edges start chipping.

Question 4. What does it have to look like?

Specify gloss as a band with a tolerance, "60 ± 5 GU at 60°", not as a single number. Gloss varies slightly with film thickness, cure and substrate, and a single-figure specification is one nobody can reliably hit.

For colour, give us a RAL number, an NCS number, or a physical sample. We match by spectrophotometer to ΔE ≤ 1.5 (CIELab), with a minimum of 100 kg per custom shade.

Common mistakes, in order of how often we see them

1. Choosing an indoor hybrid for an outdoor part to save cost. It fades within a season and gets recoated, which costs more than the correct powder would have.
2. Specifying corrosion hours without specifying film thickness. The number is meaningless without the thickness it was measured at.
3. Treating pre-treatment as the applicator's problem. It is the largest single determinant of coating life and belongs in your specification.
4. Setting oven temperature instead of metal temperature. Cure is counted from when the metal reaches temperature. A heavy part can take several extra minutes just to get there, and under-cure is invisible until adhesion fails.
5. Going thicker to be safe. Beyond the specified range you lose flexibility and impact resistance and gain edge chipping.
6. Not asking which test method produced a number. "1000 hours" means nothing without ASTM B117 and a thickness beside it.

A decision path you can follow in sixty seconds

1. Does it see daylight? Yes → Pure Polyester. Stop here unless chemicals are also involved.
2. No daylight. Are chemicals or serious corrosion involved? Yes → Pure Epoxy.
3. No. Is the priority appearance, gloss depth, or humidity? Yes → Polyurethane.
4. Otherwise → Epoxy Polyester.
5. Now fix the substrate and pre-treatment, then the film thickness, then the gloss and colour.

What to send us with an enquiry

Six lines get you an accurate quotation first time:

• The part and what it does
• Indoor or outdoor, and if outdoor, coastal or inland
• The substrate and its pre-treatment
• Shade: RAL number, NCS number, or a physical sample
• Finish and gloss band
• Quantity in kg (minimum 100 kg per shade)

Not sure which of the four applies to your part? Send us the details and we will tell you. Including when the honest answer is that you need something we do not make.