What Is Powder Coating? How the Process Works, Step by Step

The short answer

Powder coating is a finish applied as a dry powder instead of a liquid. The powder is a blend of resin, pigment and additives that control gloss, flow and hardness. A spray gun gives the powder particles an electrostatic charge, the grounded metal part attracts them and holds them in place, and an oven then melts the powder and cures it into a continuous film.

There is no solvent to evaporate. What goes on the part is almost entirely what stays on the part, which is why powder is the default finish for so much industrial metalwork: brackets, enclosures, frames, chassis, racks and equipment housings.

Powder is a thermoset, not a dried paint

Nearly all industrial spray powder is thermoset. During cure, the resin chemically cross-links into a dense network. Once cured, it does not re-soften when heated again. That cross-linking is where powder gets its hardness, chemical resistance and toughness.

Thermoplastic powders also exist. They melt and flow but don’t change chemically, and they are usually applied by dipping a preheated part into a fluidized bed. They are a niche, and a different process from production spray coating.

Industrial powders come in several resin families: epoxy, epoxy-polyester hybrid, TGIC polyester, TGIC-free (HAA) polyester, polyester urethane and superdurable polyesters. The chemistry decides whether a part can live outdoors, how it handles chemicals, and what the cure schedule is. Cardinal’s stock powders average 25 to 50 microns in particle size, finer than most people expect when they first see it.

How powder coating works, step by step

Here is the sequence a part follows on a batch powder line like ours, from receiving to packing.

1. Review the part and the callout

Before anything is sprayed, someone has to read the drawing or PO: the color, gloss and texture, the film thickness if one is specified, what must be masked, and where the part can hang. Hang points matter more than most designers realize, because the contact point is also the electrical ground and usually ends up uncoated. Our guide to designing parts for powder coating covers hang holes, tolerances and features that are hard to coat.

2. Clean and pretreat

Many adhesion and corrosion failures trace back to prep. Cardinal’s data sheets say it plainly: substrate pretreatment is a critical factor in corrosion resistance and product life.

Across the industry, prep usually means removing oil, cutting fluid, shop dirt, rust and laser or mill scale, and on many lines applying a conversion coating that improves adhesion and slows corrosion under the film. Common pairings:

• Iron phosphate on steel, typically a 2 to 5 stage wash
• Zinc phosphate on steel or galvanized, typically 5 to 9 stages
• Chrome or non-chrome conversion coatings on aluminum
• Zirconium (“transition metal”) pretreatments on lines that run mixed metals

In our shop, prep is a solvent wipe or degrease and a multi-stage wash with rinses, and parts are dried before they go to the booth. If your spec names a specific conversion coating, put it on the PO and we’ll confirm at quote time how we meet it.

Castings and hot-dip galvanized parts often get an outgas pre-bake to drive out trapped air and moisture before coating; our guide to powder coating galvanized steel and castings explains why. Where heavy rust or scale has to come off, or a spec calls for a blast profile, abrasive blasting is part of the prep. We coordinate it with a blasting partner inside the coating job, on the same quote and PO. Our prep and masking services page covers what we handle in-house.

3. Mask and plug

Threads, bores, grounding pads, bearing seats and mating faces usually need to stay bare. They are covered with high-temperature tape, caps and plugs rated for the cure. Masking is hand labor, so it is one of the biggest drivers of time and price on a part. It should be called out on the drawing, not requested over the phone.

4. Rack and ground the part

Parts hang on hooks or racks that connect them to earth ground. This is not a detail. The electrostatic process only works if the charge on the powder can bleed off through the part to ground. A poor ground means less powder sticks, coverage in recesses suffers, and film build gets uneven. Racks build up cured powder over time and have to be stripped or cleaned to keep contact good.

5. Spray the powder

There are two common ways to charge powder:

In either case, the charged powder wraps toward the grounded part, including some of the back side, and clings to it until cure. Overspray that misses the part is collected in the booth. On a reclaim booth it is sieved and reused; on a quick-color-change booth it is often scrapped.

6. Work around the Faraday cage effect

Inside corners, narrow channels and blind holes shield themselves from the electric field. Powder follows the field lines to the nearest edges and flat faces instead of reaching into the recess. This is the Faraday cage effect, and it is the main reason some features come out thin.

Operators fight it by lowering gun current, slowing powder velocity, moving the gun closer, keeping a good ground and coating the recesses first. Design helps more: wider channels, open corners and through-holes instead of blind holes all coat better and faster.

7. Cure in the oven

The oven melts the powder, lets it flow out into a smooth film, and then holds it at temperature long enough to cross-link. More on time and temperature in the next section.

8. Cool, unmask, inspect and pack

Parts cool on the rack, then masking comes off and parts are inspected. There is no air-dry or solvent flash time; once a cured part is cool, it can be handled, packed and shipped.

Inspection in the industry usually includes a visual check for coverage, runs, contamination and color, and a dry film thickness reading with a gauge per ASTM D7091 (magnetic gauges on steel, eddy-current gauges on aluminum). Specs may also call for a cross-hatch adhesion test (ASTM D3359) or a solvent-rub cure check (ASTM D5402) on a test panel. On production programs we follow the customer’s QC procedure, and we provide Certificates of Conformance on request.

Powder coating temperature: why metal temperature is what counts

A powder’s cure schedule is a time at metal temperature, not an oven setting. The clock starts when the part itself reaches the cure temperature. A thin bracket gets there quickly. A heavy weldment or thick plate can spend much longer in the oven before its cure clock even starts. Shops profile ovens with a data logger attached to a part to see the real metal temperature curve.

Typical schedules vary by chemistry and by product. A generic reference from Products Finishing (Kevin Biller, ChemQuest, 2023):

Specific products differ from that table. Cardinal’s stock TGIC polyester, epoxy, hybrid and polyurethane powders, which we coat with, are rated for 10 minutes at 400°F metal temperature. Cardinal’s C909 superdurable polyester cures at 10 minutes at 350°F. Time and temperature trade off within a window, so always go by the data sheet for the exact powder.

Two practical points for buyers:

• Your part has to survive the cure. Our process is built for metal parts that can be electrically grounded and withstand the cure temperature. Masking keeps powder off a surface, but it does not protect a heat-sensitive part from the oven. Plastic components, rubber seals, lubricants and electronics usually have to be removed before coating, or the part has to be coated before assembly or finished another way, such as liquid paint. If you’re not sure about a material, see what metals can be powder coated.
• Overbake and undercure both cause problems. Undercured powder can be soft and poorly bonded. Many powders tolerate a fair amount of extra time, but Cardinal notes slight yellowing on overbake, especially in whites and pastels.

Film thickness

Powder builds thicker than most liquid paints in a single coat. According to DeFelsko, electrostatic spray typically produces about 1 to 10 mils (25 to 250 microns), and a spec of 2 to 5 mils with about ±1 mil tolerance is common in industry. Each powder has its own tested range. Cardinal’s T009 TGIC polyester is tested at 1.5 to 3.0 mils, and its C909 superdurable at 2.5 to 4.0 mils.

Too thin, and you get poor hiding and weak corrosion protection. Too thick, and you risk incomplete cure, chipping, poor adhesion, wasted powder, more outgassing on castings, and parts that no longer fit. That last one matters on threads, press fits and mating slots. Either mask those features or design clearance for the film. If your drawing doesn’t state a thickness, our coating callout checklist shows what to include.

Transfer efficiency and VOCs

Transfer efficiency is the share of the coating that ends up on the part. In a separate 2026 Products Finishing article on powder sustainability, Kevin Biller puts powder’s first-pass efficiency at about 70 to 90 percent, against 25 to 65 percent for liquid spray, and overall powder use at 95 percent or better when overspray is reclaimed. Other industry sources quote lower first-pass figures, and part shape matters a lot: a large flat panel catches far more powder than an open wire form.

VOCs: powder has no solvent, so emissions are negligible. Booth air can be filtered and recirculated, and parts don’t need flash-off time. Some polyurethane powders release a small amount of blocking agent during cure, so “near-zero VOC” is the accurate claim.

Those two points, plus one-coat film builds and no drying wait, are why powder usually wins on cost for production metal parts. It isn’t always the right call, though. Heat-sensitive assemblies, very frequent color changes, thin-film requirements and specs that name a liquid system all point to wet paint. We compare the two in powder coating vs. liquid paint.

What this means for your next RFQ

If you’re sending parts out for powder coating, the process above suggests what to put in front of your coater:

• Material and any prior finish (bare, galvanized, cast, previously painted)
• Powder color, gloss and texture, or the exact product if you have one
• Film thickness range, if it matters to fit or performance
• Masking areas marked on the drawing
• Acceptable hang or contact points
• Quantity per run and how often the part repeats
• Any QC records or certificate you need with the shipment

We coat production runs of metal parts with Cardinal powders on a batch line in Colorado Springs. Send drawings and quantities through our request a quote form and we’ll come back with questions on anything the callout leaves open.