Powder Coating vs Paint: How to Choose

Powder coating sprays a dry, electrostatically charged polymer powder onto a grounded part. The charge makes the powder cling and wrap slightly around edges. The part then goes into an oven, typically at 180 to 200 C, where the powder melts, flows and cures into a continuous film.

Wet paint is a liquid carrying pigment and binder in a solvent or water. It is sprayed, the carrier evaporates, and the film cures either in air, with heat, or under UV depending on the chemistry.

Almost every practical difference follows from those two descriptions. The oven is why powder is unavailable on heat sensitive substrates and assemblies. The electrostatic attraction is why powder covers edges better and produces less overspray waste. The absence of solvent is why powder films are thick, and why they are hard to make thin.

This is the point that costs people parts. A powder coat film is typically 60 to 100 microns thick, and it goes on every unmasked surface. Wet paint is commonly 25 to 50 microns, and some systems go thinner.

On a flat cosmetic panel none of that matters. On a part with fits it matters enormously. A 60 micron film on both walls of a slot removes 120 microns from the slot width. A bore that was a slip fit becomes an interference fit. A threaded hole that was not masked is now a threaded hole that no longer accepts its screw.

The rules that follow are simple and routinely ignored. Mask threads, bearing bores, sealing faces, ground paths and any mating surface with a fit. Where a surface must be both coated and dimensioned, tell the shop the finished dimension and let them work back to the machined size. And if a feature genuinely cannot tolerate the film, that feature is a masking line item, which has a cost.

Ask for the coating specification on the drawing, including thickness range and which surfaces are excluded. A note saying only powder coat black leaves every one of these decisions to somebody who has not seen your assembly.

Powder wins on mechanical toughness. The film is thicker and generally more resistant to chipping, scratching and impact, which is why it dominates on tools, appliances, outdoor furniture and anything that gets handled roughly.

Powder also covers edges better. The electrostatic attraction pulls powder around sharp corners where wet paint thins out and pulls back, and edge failure is one of the most common places a painted part starts corroding.

Wet paint wins on repairability and touch up. A scratched painted part can be blended and resprayed locally. A damaged powder coat generally cannot be touched up invisibly, and the honest repair is to strip and recoat the whole part.

Both are only as good as the preparation underneath. The most common cause of a finish failing is contamination or an inadequate pretreatment, not the coating chemistry. On steel that means a phosphate or equivalent conversion coating; on aluminum, a chromate or a chrome free equivalent. If a quote seems unusually cheap, the pretreatment is usually where it was saved.

The oven rules powder out for a category of parts, and this is not negotiable chemistry.

Most plastics cannot see 180 C. Neither can assemblies containing seals, bearings, adhesives, electronics or anything with a temper you care about. Heat treated aluminum is worth checking specifically: a 6061-T6 part held near 200 C for a full cure cycle can lose some of its temper, which matters on a structural part and does not on a cosmetic one.

Wet paint has no bake requirement in most systems, which is why it is the answer for plastics, mixed material assemblies, large weldments that will not fit an oven, and anything already assembled.

Size is the other limit. Powder needs an oven the part fits inside. Wet paint needs a booth, and booths scale more cheaply than ovens do.

If you need an exact color, especially a match to an existing part or a brand standard, wet paint is the more reliable route. Paint can be custom mixed in small quantities to a specified value, and the color is verifiable before it goes on the part.

Powder is manufactured in batches. Standard RAL and common colors are readily available, but a custom color means a minimum order of powder, and batch to batch variation is a real phenomenon on critical matches. Two parts coated from different batches of nominally the same color can differ visibly side by side.

Gloss and texture behave similarly: powder offers a wide but discrete range of standard finishes, while paint is tunable. For fine metallic effects, multi coat systems and clear coats over graphics, paint has more room.

For the specification numbers themselves, thickness classes, gloss ranges and the common standards, the finish reference charts carry the tables rather than repeating them here.

Powder is cheaper per part at volume and often more expensive for one part. The reason is setup: color changeover on a powder line means purging equipment, and running a single part means the same changeover cost against one unit.

Material efficiency runs the other way and favours powder strongly. Overspray powder can be reclaimed and reused, so utilization commonly reaches 90 percent or better, while wet paint transfer efficiency is often 50 to 70 percent with the rest lost as overspray.

Masking is manual labor, and it is the line item that most often surprises people on a finishing quote.

Every masked feature is a plug, a cap, a tape line or a custom fixture, applied by hand to every part and removed by hand afterwards. Three masked threads on a part is a few seconds each. Twenty masked features on a part is a different job, and at volume it can exceed the cost of the coating itself.

Two design habits reduce it substantially. Group features that need masking onto as few faces as possible, and where a surface must stay bare for grounding or sealing, ask whether a single larger masked area can replace several small ones. And consider whether some threads can be tapped after coating instead of masked before it, which is frequently cheaper and gives a cleaner thread.

Call out masking explicitly on the drawing with a note or a marked view. Assuming a shop will infer which bores are functional is how coated bearing bores happen.

Most decisions resolve on temperature, film thickness and volume, in that order.

Send the model with a marked up view showing which surfaces must stay bare: threads, bearing bores, sealing faces, ground paths, mating surfaces with a fit. Specify the color by standard rather than by name, give a gloss level, and state the thickness range you expect.

Say where the part lives, because outdoor and UV exposure change the recommended chemistry, and say whether the part is assembled or will be assembled after finishing.

Then ask three questions. What is the pretreatment, since that determines whether the finish lasts. What does the masking add, and is there a grouping of features that would reduce it. And which dimensions should I hold at the machined stage so they land correctly after coating, given the film thickness you are quoting.