The Evolution of Powder Coatings in Fenestration Systems Over 60 Years
Posted on Tuesday, February 28, 2023
By Rich Rinka
Powder coating is an effective, durable finish for aluminum extrusions used in the fenestration industry. In architecture, fenestration refers to all openings in a building envelope, including curtain walls, windows, doors, and skylights. Powder coating protects the substrate from environmental impactors like cold, heat, and corrosive elements, while also protecting against human impacts like handling and cleaning.
While powder coating for aluminum windows, doors, and skylights has been an option since the late 1940s and early 1950s, the fenestration industry has only had material specifications for the last 60 years or so. In April of 1965, the Architectural Aluminum Manufacturers Association (AAMA) published its first standard on the topic, decades before becoming the Fenestration and Glazing Industry Alliance (FGIA) in 2020. AAMA 603.1, Specification for Decorative Painting of Aluminum Extruded Products, came in at a mere five pages of direction, compared to today’s version totaling 52 pages and spanning three separate documents, all of which were recently re-released in 2022 by FGIA.
The relatively brief 1965 standard contained 14 sections:
- Pretreatment requirements.
- Surface appearance of finished product after painting.
- Test specimens.
- Dry film thickness (for surfaces to be exposed to weather).
- Dry film hardness.
- Film adhesion (both dry and wet).
- Color uniformity.
- Specular gloss.
- Humidity resistance.
- Weather exposure (outdoor and accelerated).
- Salt spray resistance.
- Chemical resistance (mortar test and acid test).
- Ability to repair film.
- Resistance to sealants.
Just like the organization that developed the technical publication, the original 1965 standard has evolved. Today, it is a suite of three FGIA documents:
- AAMA 2603, Voluntary Specification, Performance Requirements and Test Procedures for Pigmented Organic Coatings on Aluminum Extrusions and Panels (with Coil Coating Appendix).
- AAMA 2604, Voluntary Specification, Performance Requirements and Test Procedures for High Performance Organic Coatings on Aluminum Extrusions and Panels (with Coil Coating Appendix).
- AAMA 2605, Voluntary Specification, Performance Requirements and Test Procedures for Superior Performing Organic Coatings on Aluminum Extrusions and Panels (with Coil Coating Appendix).
FGIA is always reviewing its technical standards for how they work in the fenestration industry to make sure they are meeting the industry’s needs. These standards describe laboratory test methods and performance criteria shown to be critical to coating performance. They are organized in order of basic performance, high performance, and superior performance (i.e., ‘good, better, and best’)—a triumvirate of increasingly stringent performance criteria. This tier system allows architects to choose the best and most cost-effective match for the type and location of the building as well as its typical weather exposure.
While the bones of both the 1965 original standard and the current 2022 version of the FGIA suite of aluminum finishes documents remain the same, directives like dry film thickness and test methods have changed or have been replaced by improved methods over the decades. Requirements have also become more stringent with time. For film thickness, the entry requirement for an AAMA 2603-compliant finish must be a minimum of 20 microns (0.8 mil) thick, while those meeting AAMA 2604 and 2605 must be a minimum of 30 microns (1.2 mil) thick. Additionally, new requirements for things like detergents used for cleaning powder coated window frames are now included.
All three of today’s standards test for color uniformity, specular gloss, dry film hardness, film adhesion, impact resistance, chemical resistance, resistance to corrosion caused by humidity and salt spray, and resistance to color fading or deterioration due to weathering. AAMA 2604 and 2605 add abrasion resistance to this list. For other factors, exposure conditions vary. For example, exposure time to the corrosive influences of high humidity increases across AAMA 2603, 2604, and 2605 from 1,500 hours to 3,000 hours, to 4,000 hours, respectively. Weathering test duration also increases from one year, to five years, to 10 years, respectively. Corrosion susceptibility based on reaction to salt spray testing varies among the standards as well.
The salt spray resistance test is now titled cyclic corrosion testing and calls for scoring the film deep enough to expose the base metal and exposing the sample for 2,000 hours, as directed in ASTM G85, Standard Practice for Modified Salt Spray (Fog) Testing, Annex A5, dilute electrolyte cyclic fog/ dry test. The sample is evaluated using a rating scale that is defined in ASTM 1654.
Corrosion testing has also evolved over time. FGIA has been conducting testing to evaluate alternatives for the use of salt spray fog to quantify corrosion more accurately. One of these improvements is the replacement of the ASTM B117 test with the ASTM G85 method in these specifications. ASTM B117, Standard Practice for Operating Salt Spray (Fog) Apparatus provided a controlled corrosive environment to produce relative corrosion resistance information. However, correlation and extrapolation of actual corrosion performance were not always predictable.
The cyclic corrosion testing method described in ASTM G85 is effective for evaluating a variety of corrosion mechanisms, including general, galvanic, and crevice corrosion. It is a more realistic way to simulate observed outdoor conditions than traditional steady state exposure tests, such as ASTM B117. Since actual atmospheric exposures usually include both wet and dry conditions, by using cyclic corrosion testing, accelerated laboratory tests can be patterned after these natural cyclic conditions.
The 1965 standard described pretreatment requirements as simply calling for a chemical conversion coating to be tightly adhered after drying and prior to paint application. Today’s standards go into much more detail, including identifying different surface treatment systems intended to improve the final performance of the coated parts. As an example, chromium chromate or chromium phosphate systems are required to have a minimum coating weight of 431 mg/m2 (40 mg/ft2). The requirements and comments on metal preparation and pretreatment are continuing to evolve and future versions of the AAMA 2603, 2604, and 2605 will most likely provide additional guidance in this area.
Those using powder coating for the window, door, and skylight industry should know that applicators are certified by the paint manufacturers. A coating project without the right coatings and all associated processes will not be sufficient to provide the expected long-term performance and durability. It is imperative applicators follow the processes required by the coating manufacturers, and wherever possible, have certification from the coating manufacturers. Additionally, FGIA offers a program that includes verification of paint applicator processes for fenestration materials, the Verified Components Program. Learn more at FGIAonline.org/ components.
Rich Rinka is technical manager, fenestration standards and U.S. industry affairs at FGIA.