Understanding Corrosion Testing Requirements in Architectural Performance Coatings
When specifying architectural coatings, corrosion resistance is an important consideration, particularly when coated aluminum will be exposed to moisture, salt, humidity, or other corrosive conditions.
So, what does it actually mean when a powder coating meets an AAMA performance specification?
The architectural industry relies on three major AAMA performance specifications to establish performance requirements for coatings used on architectural aluminum: AAMA 2603, AAMA 2604, and AAMA 2605. While these specifications evaluate several properties, including adhesion, impact resistance, humidity resistance, and weathering, each includes specific requirements for corrosion resistance.
Understanding how those requirements differ can help architects, specifiers, and fabricators select the appropriate coating for the application.
While these specifications are now maintained by the Fenestration and Glazing Industry Alliance (FGIA), they are still commonly referred to throughout the industry as “AAMA specs.”
AAMA Standards and Corrosion Resistance
Corrosion testing evaluates how well a coating protects the underlying metal when exposed to a corrosive environment.
One of the primary tests referenced by the AAMA specifications is salt spray testing, performed according to ASTM B117. In this accelerated laboratory test, coated panels are exposed to a controlled salt-laden environment and then evaluated for corrosion and other signs of coating failure.
Typically, the coating is deliberately scribed through to the substrate before testing. This allows evaluators to determine how effectively the coating prevents corrosion from spreading underneath the film from a damaged area.
The three AAMA specifications establish different corrosion-resistance requirements based on the intended performance level of the coating.
AAMA 2603: General Interior Performance
AAMA 2603 is generally associated with coatings intended for interior architectural applications, where exposure to outdoor weather and corrosive environments is limited.
For corrosion resistance, AAMA 2603 requires 300 hours of salt spray exposure. Following exposure, the coating is evaluated for corrosion and coating failure around the scribe.
For many interior applications, this level of corrosion resistance provides an appropriate balance of performance and cost where coated metal will not be subjected to demanding exterior conditions.
IFS 300SP is formulated to meet and exceed AAMA 2603 requirements and is designed for general interior architectural applications.
AAMA 2604: Enhanced Corrosion Resistance
AAMA 2604 significantly increases the corrosion-resistance requirement and is commonly specified for high-performance architectural applications, including many exterior commercial projects.
The salt spray requirement increases to 3,000 hours — ten times the exposure duration required under AAMA 2603.
After exposure, the coating is evaluated for corrosion and its ability to resist corrosion spreading from the scribe. The higher requirement reflects the more demanding environments in which AAMA 2604 coatings are expected to perform, including exposure to moisture, humidity, pollutants, and airborne salts.
IFS 400SD is formulated to meet and exceed AAMA 2604 requirements, providing enhanced durability for architectural applications while also supporting sustainability goals.
AAMA 2605: Superior Architectural Performance
AAMA 2605 represents the industry's highest level of architectural coating performance and is typically specified when long-term exterior durability is critical.
An important point is that AAMA 2605 also requires 3,000 hours of salt spray testing. In other words, AAMA 2605 does not simply increase the salt spray requirement beyond AAMA 2604.
Instead, the significant difference is found across the overall performance requirements. AAMA 2605 places much more demanding requirements on properties such as weathering, color retention, gloss retention, chalk resistance, and overall film performance.
This is why AAMA 2604 and 2605 should not be differentiated simply by their salt spray exposure time. AAMA 2605 represents a higher level of overall architectural performance.
IFS 500FP, a FEVE fluoropolymer powder coating, is formulated to meet and exceed AAMA 2605 requirements and is designed for demanding exterior applications where long-term performance is critical.
Salt Spray Testing Is Only Part of the Picture
It can be tempting to assume that a higher number of salt spray hours automatically means a more durable coating. In architectural coatings, however, corrosion testing is only one component of the AAMA performance requirements.
Overall coating performance also depends on factors such as resin chemistry, pigment selection, substrate preparation, pretreatment, application, film thickness, and cure.
This is especially important when comparing AAMA 2604 and AAMA 2605. Both require 3,000 hours of salt spray exposure, but AAMA 2605 demands a substantially higher level of overall performance across the specification.
Powder and Liquid Coatings: Same AAMA Requirements
Another common misconception is that AAMA requirements apply differently to powder and liquid coatings.
They don't!
The AAMA specifications establish performance requirements for architectural coatings regardless of whether the coating is applied as a powder or liquid. Both technologies must demonstrate compliance with the applicable requirements.
The difference is in the chemistry and formulation used to achieve that performance.
Modern architectural powder coatings can meet demanding corrosion and weathering requirements while offering the application, environmental, and material-efficiency advantages associated with powder coating.
Choosing the Right Corrosion Performance
Understanding the corrosion requirements behind AAMA 2603, 2604, and 2605 is an important part of selecting the right architectural coating.
AAMA 2603 provides a level of performance appropriate for many interior applications. AAMA 2604 provides enhanced performance for more demanding architectural environments, while AAMA 2605 combines stringent corrosion requirements with the industry's highest overall level of architectural coating performance.
Ultimately, the right specification depends on the environment, substrate, expected service life, and overall performance requirements of the project.
Remember: salt spray hours are only one piece of the puzzle. A durable architectural coating system depends on the complete combination of coating chemistry, pretreatment, application, and cure.