For most metal products the honest default is powder coating: it is tougher, cheaper at volume, and environmentally simpler. Wet paint wins when you need a very thin film, an exact color or specialty finish, a coating on a heat-sensitive assembly, or a run so small that no coater wants to set up a powder line for it. That is the whole decision in two sentences — the rest is knowing which of those exceptions applies to your part.

How Powder Coating Works

Dry pigmented polymer powder is electrostatically charged and sprayed onto a grounded metal part. The powder clings, and the part goes into an oven where the powder melts, flows out, and cures into a continuous film. No solvent is involved. Overspray can often be reclaimed and reused, so material utilization is high.

Consequences worth knowing:

  • The part must conduct and must survive the oven. Cure temperatures are high enough to distort thin sheet, damage plastics, and destroy electronics. Coat bare metal parts, then assemble.
  • Films are relatively thick. Powder builds a heavier film than wet paint, which is great for durability and bad for tight-fitting features. Mask threads, bearing bores, ground points, and mating surfaces, and add the film thickness into your tolerance planning.
  • Edge coverage is excellent. Electrostatics drive powder onto edges and corners, which is exactly where wet paint tends to thin out and fail first.
  • Deep recesses can starve. Faraday cage effects make interior corners and deep pockets hard to coat evenly.

How Wet Paint Works

Liquid paint — solvent-borne or waterborne — is sprayed and then either air-dries, cures at moderate temperature, or cross-links chemically as a two-component system. Multi-stage systems are normal: primer, base, and clear.

  • Very thin, very controlled films. When a part has to fit into a precise assembly, or when a coating must not soften a fine texture, wet paint is the answer.
  • Any color, any gloss, any effect. Metallics, pearls, soft-touch, dead-flat matte, and exact brand-color matching are all easier in liquid. Small custom color batches are far cheaper to mix than a custom powder lot.
  • No oven required. Heat-sensitive substrates, already-assembled products, plastics, and mixed-material assemblies can be wet painted.
  • Touch-up and repair are practical. A scratched wet-painted panel can be blended in the field. A powder-coated panel generally cannot.
  • Solvents and VOCs. Liquid systems bring ventilation, waste handling, and air-permit considerations that dry powder does not. Requirements vary by state and locality, so treat this as a question for your coater and, where relevant, a qualified environmental consultant — this article is educational only and is not regulatory or legal advice.

Point by Point

  • Abrasion and impact durability: powder, clearly. The thicker cross-linked film resists chipping in ways a typical wet film does not.
  • Corrosion protection: powder has the edge on uniformity and edge coverage, but pretreatment dominates the outcome for either system. A zinc phosphate or equivalent conversion coating matters more than the topcoat choice.
  • Cost at volume: powder wins — fewer coats, no solvent, reclaimable overspray, faster line throughput.
  • Cost at low volume: wet paint often wins, because powder means a color changeover and an oven cycle for a handful of parts. Sticking to a standard stocked powder color is the way to keep low-volume powder affordable.
  • Color and finish precision: wet paint, especially for exact matches and specialty effects.
  • Thin-film and tight-tolerance parts: wet paint.
  • Heat-sensitive or assembled parts: wet paint, or a low-temperature-cure powder if the substrate allows.
  • Environmental and worker exposure: powder is the simpler story.

So What Should Your Product Use?

Powder coat if the part is bare steel or aluminum, gets handled or knocked around, sees weather, or ships in volume — enclosures, frames, brackets, chassis, outdoor housings, tool bodies. Wet paint if the part is plastic or a mixed assembly, if a specific brand color or a metallic or soft-touch effect is central to the design, if the film must be thin, or if you are building tens rather than thousands.

Two alternatives are worth considering before you spray anything at all. Anodizing gives aluminum a hard, integral, very thin surface with no added film thickness to speak of — often a better answer than paint for machined aluminum parts, and worth pricing against coating (see anodizing aluminum cost). And for some products a properly specified material with a molded-in or mill finish removes the coating operation entirely, which is the cheapest finish there is.

Design Decisions That Come Before the Coater

A part designed for coating is much cheaper to coat. Give the finisher hang points or fixture holes in non-cosmetic locations. Avoid blind pockets that trap pretreatment chemicals or starve of powder. Keep sharp burrs and weld spatter off cosmetic faces, because coating amplifies rather than hides them. Specify which surfaces are cosmetic and which are functional, and mark masked areas explicitly on the drawing. If the part is sheet metal, these choices interact directly with bend reliefs and hem design — see our sheet metal design guide.

Material choice matters too. Steel and aluminum both coat well but need different pretreatment, and their base cost and stiffness differ enough that the decision should be made on the whole part, not the finish alone — our comparison of aluminum vs steel covers that. And the finish is part of the product's identity, not just its protection, which is why gloss level, texture, and color belong in a deliberate CMF design decision rather than being left to the coater's default.

What to Settle With the Finisher Before You Start

  1. Exact color reference and gloss level, with an approved sample you keep.
  2. Film thickness range, and where it is measured.
  3. Pretreatment process and whether it suits your substrate.
  4. Masking requirements — threads, grounds, mating faces, labels.
  5. Adhesion and, if the product goes outdoors, salt spray or accelerated weathering expectations.
  6. How rework and rejects are handled, and who pays for them.

Always approve a first-article sample under the lighting the product will actually live in. Colors that match under shop fluorescents can diverge badly in daylight. If you are still at the prototype stage, note that finishing prototypes uses different methods entirely — see painting and finishing prototypes for how to make a pre-tooling model look like the real thing.

Projects House specifies and manages finishing as part of production engineering — drawings, masking callouts, supplier selection, and first-article approval. If you have a metal product and are unsure which finish will hold up in your customer's environment, get in touch through our contact form and we will help you specify it properly.