Powder coating thickness looks like a simple finish requirement, but it affects fit, assembly, grounding, thread engagement, gasket compression, hinge movement and cosmetic appearance. If the RFQ only says “powder coat black,” the supplier may quote a finish that looks acceptable but creates downstream assembly problems.
For sheet metal parts, powder coating should be specified as a controlled finish: pretreatment, color, texture, dry film thickness, masking, edge coverage, inspection and packaging.
The practical answer - Define powder coating thickness as a functional requirement, not only a color. State target dry film thickness range, masked grounding areas, threaded features, gasket surfaces, cosmetic class, adhesion expectation and inspection method. Tight mechanical interfaces should account for coating buildup on both mating surfaces.
Why dry film thickness matters
Dry film thickness, often called DFT, is the cured coating thickness on the part. Too little coating can reduce corrosion protection and coverage. Too much coating can cause fit problems, orange peel, poor edge definition, blocked holes and assembly interference.
DFT matters most at:
- Sliding or mating surfaces.
- Hinges and latch interfaces.
- Gasket compression flanges.
- PEM nuts, studs and standoffs.
- Threaded holes.
- Grounding pads.
- Tight slots and tabs.
- Cosmetic visible panels.
- Door seams and corners.
The drawing should define which areas are cosmetic, which are functional and which should remain uncoated.
Coating buildup changes fit
Powder coating adds thickness to every exposed surface. If two coated parts slide together, the coating buildup can affect both sides of the clearance. A slot that fits in bare metal may bind after coating.
Designers should review:
- Tab-and-slot clearances.
- Door-to-frame gaps.
- Hinge knuckle clearance.
- Inserted hardware clearance.
- Mounting rail fit.
- Removable panels.
- Gasket grooves and compression stops.
For assemblies, specify whether dimensions apply before coating or after coating. If final fit matters, inspect the coated part or complete assembly, not only the raw metal.
Pretreatment still decides durability
Thickness alone does not guarantee coating performance. Pretreatment controls adhesion and corrosion resistance. Poor cleaning or conversion coating can cause peeling even when DFT looks correct.
A practical powder coating plan includes:
- Degreasing and cleaning.
- Oxide or rust removal.
- Conversion coating or appropriate pretreatment.
- Dry-off before powder application.
- Correct cure schedule.
- Inspection for coverage, adhesion and defects.
For more detail, see our powder coating pretreatment guide.
Masking and grounding areas
Many industrial sheet metal parts need uncoated conductive areas. These can include:
- Grounding studs and bonding pads.
- EMI contact areas.
- Weld nuts or threaded holes.
- Mounting points for electrical components.
- Areas later welded or soldered.
- Precision datum pads.
Masking should be shown on the drawing or an annotated image. Verbal instructions are easy to miss, especially when the part has many holes or symmetric features.
Common powder coating defects
Watch for:
- Thin coverage on sharp edges.
- Excess buildup in corners.
- Orange peel on visible panels.
- Pinholes or outgassing.
- Contamination bumps.
- Poor adhesion.
- Color mismatch between batches.
- Coated threads.
- Damaged edges after packing.
Some defects are cosmetic; others affect corrosion, assembly or electrical function. Define the acceptance level based on the product, not a generic finish note.
RFQ wording buyers can use
Use wording like this:
Powder coat per approved color and texture sample. Confirm pretreatment, target dry film thickness range, masked areas, grounding points, threaded features, cosmetic faces, adhesion check and packaging method. Dimensions marked critical are required after coating unless noted otherwise.
Attach a marked-up drawing for masking and cosmetic class. It is faster than explaining finish details in email.
How DRAmetal supports powder coated assemblies
DRAmetal reviews coating thickness together with fabrication and assembly. Use the sheet-metal surface-finishing service to specify dry-film thickness and masking, then check the effect on a custom control cabinet or other assembled enclosure before releasing the finish schedule.
If your enclosure or bracket has tight fit areas, send the assembly model and finish notes. We can help define practical coating and masking requirements before production.
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