Specifying Powder Coating for Aluminum Extrusions

Aluminum extrusions look straightforward to coat – until a facade starts chalking after three years or a profile arrives with thin edges. Specifying powder coating for architectural aluminum means choosing a complete system: the right pretreatment, the right resin family, the right film build, and the right way to measure quality along a long profile. This guide covers each decision.

Why Aluminum Needs Different Pretreatment Than Steel

Steel relies on blasting and phosphate conversion layers for adhesion, while aluminum brings its own natural oxide layer and a different corrosion chemistry. For architectural extrusions the modern standard is a chrome-free conversion coating that prepares the surface without hexavalent chromium chemistry. The pretreatment step is where most long-term adhesion failures begin: a profile that looked perfect at the factory can delaminate on a facade if the conversion layer was skipped or too thin.

Choose the Resin System by Exposure, Not by Price

Interior profiles are fine with standard polyester. For exterior facades, window frames and curtain wall systems, specify a super-durable polyester or a PVDF-based system depending on the project: super-durable polyester gives excellent color and gloss retention at a practical cost, while PVDF is chosen for landmark projects where the spec demands the highest weather resistance. Ask for the manufacturer data on chalking, color retention and gloss retention over the design life of the building.

Film Thickness and Gloss for Architectural Quality

• Exterior architectural profiles: typically 60-100 microns (2.4-3.9 mils) dry film
• Interior profiles: 50-80 microns is usually sufficient
• Gloss: state a target range, e.g. 30-40 gloss units, not a single number
• Edge coverage: measure at corners and cut ends, not only on flat faces

Color and Gloss Consistency Along a Long Profile

A 6-meter profile shows color variation more brutally than a small panel. Metallic and mica finishes are especially sensitive to spray distance, voltage and film thickness along the length. Specify the acceptable delta-E against the approved master, require measurement at multiple points along the profile, and keep the approved sample and production check panels together so the coating supplier and the coater are judging against the same reference.

Handling, Masking and Racking Marks

Aluminum profiles are soft enough that handling damage shows immediately under a gloss coating. Decide in advance where racking marks are acceptable, whether masking is required for mating surfaces and threaded holes, and how profiles will be packed for transport. These small decisions, written into the spec, prevent the most common disputes on architectural orders – marks, scratches and coated surfaces that should have stayed bare.

QA on Long Profiles: Measuring Along the Length

• Measure film thickness at the two ends and the middle of each sampled profile
• Check adhesion with a cross-cut test at a cut end and on a flat face
• Verify color against the approved master under standard light
• Keep one coated profile section from each batch as a retained reference

Specify the System, and the Supplier Will Follow

Send us the profile cross-section, the design life and exposure class of the project, and your approved color sample. We will confirm the pretreatment, resin system, film thickness and QA plan, and provide a technical data sheet your architect or quality team can sign off before production starts.