Powder Coating vs Liquid Paint — Choosing a Metal Finishing System per ASTM B117, Qualicoat in Thailand

See the whole-system guide: the Metal Fabrication / machine-shop fit-out guide — this article is one step — see the end-to-end fit-out guide.

Metal parts made in a factory — steel frames, electrical enclosures, racks, brackets, steel furniture, aluminium profiles — need a surface finish for corrosion protection, appearance, and service life. The question at order time: "powder coating or liquid (wet) paint?"

Both finish metal, but the process and properties differ clearly — choose wrong and the finish fails, or you overpay. This article compares them by standards and real use.

1. The Difference Is in the Process

Powder coating = a thermoset powder (epoxy/polyester) applied electrostatically to the part, then baked at ~180-200°C to melt and cure into a hard film.

Liquid (wet) paint = a liquid sprayed/applied, then air- or low-bake-dried — epoxy, PU, acrylic, fluoropolymer, etc.

2. Property Comparison

3. How to Choose

flowchart TD
  A[Metal part] --> B{Fits the oven?
+ withstands 180-200C}
  B -->|No - large/installed/heat-sensitive| C[Liquid Paint]
  B -->|Yes| D{Need multi-color/
special shade/matching?}
  D -->|Yes| C
  D -->|No - single color, high volume| E{Need high durability
+ no VOC?}
  E -->|Yes| F[Powder Coating]
  E -->|Not essential| G[Choose by cost/lead time]
  F --> H[Reference Qualicoat/AAMA
by required life]
  C --> H

Selection summary:

• Large/installed/multi-color/matching → liquid paint
• Single color, high volume, high durability, no VOC → powder coating
• Sun-exposed architectural aluminium → reference AAMA 2604/2605 or Qualicoat

4. Standards Used to Reference Quality

• ASTM B117 — salt spray (corrosion resistance)
• ISO 8130 — coating powder test methods
• ASTM D3359 — adhesion (tape test)
• AAMA 2603/2604/2605 + Qualicoat — durability grades for architectural aluminium (2605/Qualicoat Class 2-3 = fluoropolymer, highest sun resistance)

5. Checklist Before Ordering Metal Finishing

1. Measure the part against the oven — over-size = must use liquid
2. State the environment (indoor/outdoor/coastal) → set grade/salt-spray
3. Choose color/shade — multi-color/matching = liquid suits better
4. Specify the grade (AAMA/Qualicoat) for sun-exposed work
5. Ask for test results salt spray / adhesion + surface pre-treatment before coating

We supply and coordinate complete metal finishing — both powder coating and liquid paint to ASTM B117 / Qualicoat / AAMA — with guidance on choosing the system by part size, environment, color, and required life, including pre-treatment and test results for acceptance.

Talk to our engineering team to choose a cost-effective, durable finishing system — call 02-096-2118 or LINE OA @sahawatt1988.

Summary

• Powder coating = thicker, more durable (B117 500-2,000 h), no VOC, but needs an oven (size limit) and offers fewer colors
• Liquid paint = works on large/installed parts, multi-color/matching, easy repair, but thinner and has VOC
• Decide by part size + color + durability + VOC + volume
• Sun-exposed architectural aluminium → reference AAMA 2604/2605 or Qualicoat
• Reference quality with ASTM B117 (salt spray) + ASTM D3359 (adhesion)

Match the system to the job for a durable, cost-effective finish — neither overpaying nor peeling early.