What is Powder Coating? A Complete Guide
Powder coating is a dry finishing process in which electrostatically charged polymer powder is sprayed onto a grounded metal part and then cured under heat, where it melts, flows and chemically crosslinks into a single continuous film. There is no solvent at any stage, so there is nothing to evaporate. Which is why powder coating emits no volatile organic compounds and produces no liquid hazardous waste.
It is not paint applied differently. It is a different class of material with different physics, and understanding that difference is what lets you specify it properly.
How it works, stage by stage
1. Surface preparation
The metal is degreased, stripped of rust and mill scale, and given a chemical conversion coating: typically zinc phosphate on steel, or a chromate or chrome-free treatment on aluminium. It is then rinsed, usually with demineralised water, and dried completely.
This stage determines coating life more than any other single factor, including the choice of powder. A premium coating over an unwashed surface fails faster than a basic coating over correctly prepared metal. Most coating failures that get blamed on the powder originate here.
2. Application
Powder is fluidised in a hopper, aerated until it behaves like a liquid, then pumped to a spray gun. The gun charges each particle, either by corona (a high-voltage electrode ionising the air) or by tribo (friction against the gun barrel). The part is electrically grounded, so charged particles are attracted to it and cling by electrostatic force alone.
Because the attraction is electrostatic rather than mechanical, powder wraps around edges and reaches surfaces the gun is not pointing at. It also means powder cannot run or sag, because nothing is flowing yet.
3. Curing
The coated part enters an oven. As the metal reaches temperature the powder melts, flows out into a smooth continuous film, and then crosslinks, a chemical reaction between resin and curing agent that forms a three-dimensional molecular network. Once crosslinked, the film cannot be remelted. That irreversibility is what makes it a thermoset.
The critical detail: cure is counted from when the metal reaches temperature, not from when the part enters the oven. A heavy or thick-walled component can take several extra minutes just to come up to temperature. Get this wrong and you have an under-cured film that looks perfect and fails on adhesion.
Typical Oracle Industries cure schedules: 180–200 °C metal temperature for 10–15 minutes; Pure Epoxy dead matt at 200 °C; low-cure formulations at 140–160 °C for heat-sensitive substrates.
Why it outperforms liquid paint
| Powder coating | Liquid paint | |
|---|---|---|
| Solvent content | None, 100 % solids | Typically 40–60 % solvent by volume |
| VOC emissions | Zero | Significant; often regulated |
| Overspray | Reclaimed and reused | Waste; disposal cost |
| Material utilisation | Up to ~95 % with reclaim | Commonly 40–60 % |
| Film build per pass | 60–120 µm in one pass | Multiple coats needed |
| Runs and sags | Cannot occur | A constant risk |
| Cure time | 10–20 minutes | Hours to days |
| Impact resistance | High, thermoset network | Generally lower |
| Hazardous waste | None liquid | Solvent and sludge |
Where powder coating is not the right answer
An honest guide has to include this, and most do not.
- The part must survive the oven. Anything that cannot take 140–200 °C: most plastics, wood, assemblies with seals, gaskets, bearings or electronics: is out, unless it can be masked or disassembled.
- Very large or very heavy parts need an oven big enough to hold them and enough energy to bring the metal to temperature.
- Touch-up is difficult. Damaged powder coating cannot be spot-repaired the way liquid paint can. Repair usually means stripping and recoating.
- Very thin films are hard to achieve. Below roughly 40 µm, coverage becomes unreliable.
- Small batches with many colours can be uneconomic. The colour change and cleaning cost is fixed regardless of quantity.
- Complex internal geometry suffers from the Faraday cage effect, where the electrostatic field cannot reach into deep recesses.
The four thermosetting chemistries
| Chemistry | Best for | Weakness |
|---|---|---|
| Epoxy polyester (hybrid) | Indoor decorative metal, furniture, shelving, appliances, panels | Chalks under UV. Indoor only. |
| Pure polyester | Anything outdoors, architectural aluminium, railings, outdoor furniture | Lower chemical resistance than epoxy |
| Pure epoxy | Chemical and corrosion service, pipes, valves, tanks, enclosures | Not UV stable at all |
| Polyurethane | Premium appearance and humidity resistance | Higher cost; narrower cure window |
The selection rule is simpler than it looks: if the part sees daylight, it needs polyester. Everything else is secondary.
What performance actually looks like
Oracle Industries tests every product line in its own laboratory and publishes the reports in full. Representative values, on 0.8 mm panels with zinc phosphate pre-treatment at 70–80 µm:
| Property | Method | Result |
|---|---|---|
| Cross-hatch adhesion | ASTM D3359 / ISO 2409 | 5B / GT-0 |
| Pencil hardness | ASTM D3363 | H–2H |
| Impact resistance | ASTM D2794 / ISO 6272 | ≥100–120 kg·cm² |
| Mandrel bend, 5 mm | ASTM D522 | Pass, no cracking |
| Erichsen cupping | ISO 1520 | ≥5 mm |
| Salt spray | ASTM B117 / ISO 9227 | 500–1300 hrs by chemistry |
| Humidity | ASTM D2247 | 800–1500 hrs by chemistry |
| Storage stability | Internal | 12 months, cool and dry |
Common questions
Is powder coating better than paint?
For most metal components, yes: on durability, environmental impact and material efficiency. But it is not universally better: liquid paint wins where the part cannot be heated, where the item is too large for an oven, or where field touch-up matters.
What metals can be powder coated?
Mild steel, galvanised steel, aluminium, cast iron and magnesium alloys. Galvanised and cast surfaces need preheating to prevent outgassing.
How thick should the coating be?
Generally 60–80 µm indoors and 80–120 µm for exterior or aggressive industrial service. Too thin loses corrosion protection; too thick loses flexibility and chips at edges.
Can powder coating be applied over rust?
No. It is a barrier coating, not a rust converter. Over rust it bonds to loose oxide and lifts as corrosion continues underneath.
How long does it last?
Indoors, correctly applied, generally the life of the product. Outdoors it depends on chemistry, film thickness, pre-treatment and environment. Which is why exposure is the first question to settle.
Working out which coating your application needs? Read our selection guide browse the glossary or ask us directly.