Powder Coating
April 2026 · 6 min read
Powder coating is one of the most durable and environmentally clean metal finishing processes available. Here is a step-by-step explanation of how the process works, from raw metal to finished product.
Powder coating is used widely across New Zealand for switchboard enclosures, agricultural equipment, outdoor furniture, architectural metalwork, and industrial components. The finished product is a tough, even coating that holds up far better than liquid paint in demanding conditions. Clive Wilson Powder Coating has been applying industrial and commercial finishes from our Invercargill facility for over 50 years. Here is exactly how the process works.
Surface preparation is the most critical stage of the process. A powder coat is only as good as the surface it goes on. Any contamination, rust, mill scale, or residual oil will cause adhesion failure, corrosion under the coating, or a visible surface defect in the finished product.
Depending on the substrate and its condition, preparation involves one or more of the following:
The right combination depends on the metal type, its condition, and the performance requirements of the finished coating. Cutting corners on preparation is the single most common cause of premature powder coat failure.
The prepared part is hung on a grounded rack and moved into the spray booth. An electrostatic spray gun charges the dry powder particles as they pass through the nozzle. Because the part is electrically grounded, the charged particles are attracted to the metal surface and wrap around it, providing good coverage on edges, internal faces, and complex shapes.
At this stage, the powder is held to the surface by electrostatic attraction only. It has not formed a coating and can be brushed off. The part moves carefully to the curing oven without disturbing the powder layer.
The coated part goes into the curing oven at 180 to 200 degrees Celsius for 10 to 20 minutes, depending on the powder specification and the thermal mass of the part. The heat causes the powder to melt, flow across the surface, and then cross-link chemically into a hard, continuous film as it cures.
This cross-linking reaction is what gives powder coating its mechanical strength, chemical resistance, and adhesion. The resulting film is bonded to the metal at a molecular level, not simply sitting on top the way liquid paint does. It cannot be peeled, and it does not soften with heat at normal operating temperatures.
Parts are allowed to cool after the oven before handling. The coating reaches full hardness as it cools and is ready for use or further finishing once it reaches ambient temperature. Parts are then inspected for coverage, adhesion, and surface quality before release.
Common defects that inspection checks for include:
Good preparation and controlled application minimise these issues. Our quality procedures include film thickness measurement and adhesion testing on every production batch.
For applications with higher corrosion requirements, a two-coat system is specified. A primer powder is applied and cured first, then the top coat powder is applied and cured in a second oven pass. This adds cost but significantly improves corrosion performance and coating durability.
| System | Application | Corrosion Rating |
|---|---|---|
| Single coat | Indoor, sheltered outdoor | C2–C3 |
| Phosphate + single coat | Standard outdoor NZ | C3–C4 |
| Zinc primer + top coat | Coastal, high humidity | C4–C5 |
| Galvanise + zinc primer + top coat | Marine, industrial | C5–CX |
Most conductive metals can be powder coated, including mild steel, galvanised steel, aluminium, stainless steel, brass, and copper. The part must be conductive for the electrostatic application to work and must withstand oven curing temperatures without distortion or damage.
This rules out most uncoated plastics and any assemblies with heat-sensitive components such as pre-fitted seals, bearings, or electronics, unless low-cure powder chemistries are used.
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