Powder coating vs wet paint for metal parts: how do you choose?

The short answer

Two processes, one decision

Both finishes protect metal, and the gap between them is not quality but mechanism. Powder coating starts as a dry thermoset powder, usually polyester, epoxy or a hybrid, that is given an electrostatic charge and sprayed onto a grounded part. The powder sticks by attraction, the charge repels any excess so the build stays even, and the part then goes into an oven where the powder melts, flows and cross-links into a continuous film. Wet paint starts as pigment suspended in a solvent or water carrier, is sprayed or brushed on, and hardens as the carrier evaporates or as a low-temperature bake cures the resin. Everything that separates the two, from film thickness to environmental footprint to how you repair a scratch, follows from that one difference between a dry powder and a liquid.

Powder coating against wet paint, side by side

Put the numbers on one table and the trade becomes clear. Powder coating builds 60 to 120 microns in a single pass, because the electrostatic attraction keeps depositing powder until the layer insulates the surface, and a heavy functional grade reaches 150 to 250 microns. Wet paint lays down only about 15 to 20 microns per coat and typically needs three or four passes to reach a comparable barrier, which is more labour and more chance of a run or a sag. That thickness difference is what buys the durability: decorative powder has shown over 1,000 hours of neutral salt spray where wet paint systems commonly land at 200 to 500 hours. Powder also produces no volatile organic compounds, its overspray can be reclaimed, and material utilisation reaches 95 percent or more with a recovery system against 30 to 50 percent for a liquid spray line.

Film thickness decides the protection

The reason powder coating outlasts wet paint in the field is mostly film thickness, and thickness is also what constrains the design. A decorative powder coat is thick enough to bury a shallow laser etch and to change the fit of a close-tolerance assembly, so any surface that must mate, seal or thread has to be masked or allowed for. Functional powder at 150 microns and above is a genuine barrier against impact and abrasion, but it is also brittle enough to crack if the coating is asked to flex across a sharp bend, which is why the part should be designed with radii rather than knife edges. Wet paint gives a thinner, more conformable film that moves with a flexing panel and costs far less to build up on a complex shape, at the price of a shorter service life in a corrosive environment.

Where powder coating is the wrong choice

Powder coating has three hard limits. It needs the part to survive the cure oven, so plastics, heat-treated assemblies, soldered joints and anything with a temperature-sensitive label are ruled out; wet paint or a low-bake system is the only option there. It needs a conductive substrate to hold the electrostatic charge, which excludes bare plastic, glass and composites unless they are given a conductive primer. And it cannot match an arbitrary colour: the powder is a fixed solid pigment, so a metallic, a pearlescent, a soft-gloss spot colour or a tight brand blue often cannot be produced, while wet paint matches any shade. A fourth, softer limit is repair: a powder film damaged on site cannot be blended invisibly, whereas a wet-painted part can be touched up with the same paint and a brush.

Where wet paint earns its place

Wet paint remains the right answer in four situations. Small batches and one-off prototypes rarely justify a powder line and its oven cycle, and a 2K polyurethane or epoxy paint gives a serviceable finish in minutes. Colour-critical work, such as a customer shade chart, a metallic automotive effect or a multi-layer decorative scheme, is wet paint territory. Heat-sensitive assemblies must be painted. And parts that will be handled or serviced in the field benefit from a finish that can be repaired on site rather than returned to a coater. Chemical and solvent resistance is another wet-paint niche, because high-build epoxy and polyurethane systems can be formulated for environments where a standard powder would soften.

What to write in the finish note

The finish note decides whether the order is quoted correctly, so it should name the process or the standard, give a thickness range rather than a single figure, state whether dimensions are controlled before or after coating, and list the surfaces that must stay bare. Masking is the most commonly forgotten line: threads, bores, press fits, sealing faces and electrical grounding points all need to be excluded, and both powder and paint will change a mating dimension. If the part must also be tested, say so, because a salt-spray or adhesion result costs extra and takes time. All the figures here are planning ranges for standard lines; the film a given shop delivers depends on the resin, the substrate and the cure, so a thickness measurement and a salt-spray result on your own part are the numbers that settle a specification.

See surface finishing for the coating routes we run, sheet metal fabrication for the brackets, panels and enclosures that most often go to a powder line, and die casting for cast housings that need a conductive substrate before coating.