Powder coating or anodising on aluminium are just like any protective coating on metal. The durability will depend on the exposure zone they are in. Although aluminium is a durable metal, when exposed it will degrade in appearance over time, and it is also true of aluminium finishes. So specifying the right finish for the the exposure zone is important.
For powder coating the industry generally uses the American Architectural Manufacturers Association (AAMA) test documents to define the performance of powder coating in different environments. These are:
- AAMA 2603 - Extra-durable polyester powder coating (recommended for maximum exposure zone C, to NZS 3604).
- AAMA 2604 - High-durability polyester powder coating (recommended for maximum exposure zone D, to NZS 3604).
- AAMA 2605 - High-durability fluoropolymer powder coating (recommended for maximum exposure zone E to NZBC E2/AS1, and most geothermal / micro-climates).
For a number of years anodising thickness / grade has been defined by the Window and Glass Association New Zealand (WGANZ) (and WANZ before that), as AA12, AA20, and AA25. These relate to exposure zones as follows:
- AA12 - 12 microns minimum (recommended for maximum exposure zone B, to NZS 3604).
- AA20 - 20 microns minimum (recommended for maximum exposure zone C, to NZS 3604).
- AA25 - 25 microns minimum (recommended for maximum exposure zone D to NZS 3604, and zone E to NZBC E2/AS1, and most geothermal / micro-climates).
BRANZ have released a new Bulletin BU 634 "Finishing Aluminium" (replacing BU 349), which covers the subject in great depth. Recommended reading if you want to know more detail.
Where appropriate, Masterspec have updated standards in the Documents clause, and guidance notes.
Powder coating and anodising finishes are categorised by minimum standard for coating thickness to AAMA and WGANZ respectively. The Q+A is structured to align with exposure zones set out in NZS 3604, and NZBC E2/AS1.
Exposure zones are sometimes derived from other standards.
To help with this, our Table 1 (expanded from previous articles) illustrates how they roughly relate.
Table 1 - Comparison across Standards for Exposure Zones / Corrosion Zones
Acknowledgement: BRANZ Build June/July 2013 and NATSPEC NTN DES 010, for part of the information.
1) Corrosion Risk descriptions from AS/NZS 2312.1: 2014.
2) 9223 is used by the coil coaters for metal roofing and cladding.
3) AS/NZS 2728: 2013 - describes product types, linked with AS/NZS 2312, and ISO 9223
4) 2699 set, parts 1 to 3, deals with components for masonry.
5) E on its own or divided into EI Very High Industrial and EM Very High Marine.
6) C5 on its own or divided into C5I Very High Industrial and C5M Very High Marine.
7) SED specific design, particularly for extreme marine, geothermal, and micro-climate
8) Extreme marine or extreme industrial.