Powder Coating & Paint: Guidance for Design Engineers

Powder coating and conventional liquid paint are two of the most common ways to finish metal parts. They both protect against corrosion, wear, and UV damage, and can provide virtually any color or texture. But they behave differently in practice—how they're applied, how thick they are, how durable they are, and even how they interact with part geometry all vary. Understanding these differences early helps prevent surprises in manufacturing and assembly.

This guide gives engineers a practical overview of each process, explains where they overlap and where they differ, and highlights the considerations you need when specifying finishes for CNC-machined or fabricated parts.

What Powder Coating and Paint Have in Common

Despite their differences, both finishes share some fundamental principles:

• Protection: Both provide corrosion, wear, and UV resistance.
• Aesthetics: Both allow for color, gloss, and texture customization.
• Thickness: Both add measurable material to the surface.
• Adhesion matters: Clean, properly prepared surfaces are essential for long-term performance.
• UV stability: Both can be formulated to resist fading outdoors.

How They Differ

Materials and Surface Preparation

Powder Coating

• Works best on steel, stainless steel, aluminum, and zinc-plated surfaces
• Requires clean, dry, and often pre-treated surfaces (e.g., chemical conversion or phosphate coatings)
• Electrostatic application works best on conductive parts

Liquid Paint

• Common for steel, aluminum, some plastics
• Needs cleaning, degreasing, and sometimes primer
• Primer improves adhesion, corrosion resistance, and color consistency

Dimensional Considerations

Both processes add material to surfaces, which can affect:

• Sliding fits or tight assemblies
• Threads or press-fit areas (masking may be required)
• Sealing surfaces

Typical thickness ranges:

• Powder coating: 1-4 mils (25-100 µm)
• Liquid paint: 1-5 mils (25-125 µm)

While these coatings are softer than plating, even small thicknesses can interfere with precision fits, so designers should account for them in drawings and tolerances.

Performance and Durability

Powder Coating

• Excellent scratch, chip, and chemical resistance
• Best for industrial machinery, outdoor structures, and high-wear parts
• Hard finish may be brittle on thin or flexible parts

Liquid Paint

• Softer, more flexible
• Easier to touch up or repair
• Can be formulated for UV and chemical resistance, but more sensitive to mechanical damage

When to Choose One Over the Other

Powder Coating

• Industrial or structural steel parts
• Outdoor furniture or architectural components
• Automotive panels requiring high durability and uniform finish

Liquid Paint

• Small batch runs or custom colors
• Complex parts with internal recesses, threads, or tight assemblies
• Applications requiring frequent touch-ups or color changes

Special Considerations

• Both coatings cannot penetrate threads or press-fit tolerances without masking.
• Powder coating requires curing ovens; liquid paint can often be air-dried or baked.
• High-end processes sometimes use electrocoat (e-coat) primers to enhance corrosion resistance before powder or paint—common in automotive or outdoor applications.

Practical Takeaways for Design Engineers

• Always consider the added thickness when designing fits, threads, and seals.
• Decide early if internal or threaded surfaces need masking.
• Powder coating is hard and durable but harder to repair; paint is **easier to touch up** but softer.
• Surface preparation and cleanliness are critical for both methods.
• When in doubt, check with your shop—each facility may have process limitations that affect your part.