Volume 13, Issue 6 - July/August 2012
Handle with Care
The smell of the fresh salt air reminds us not only of summer days at the beach but also of how window finishes perform in corrosive environments. Protecting metal framing—particularly aluminum—comes to mind.
Aluminum-framed windows are popular in several niche residential markets that provide a mainstay, if not a resurgence, of demand for aluminum products. A primary example of these is hurricane- and impact-resistant windows, now mandated by codes in most jurisdictions along the Atlantic and Gulf coasts and feature aluminum frames for their inherent strength.
An anodized finish must pass tests for color and gloss uniformity, abrasion and corrosion resistance, and resistance to “crazing” (the formation of a network of fine cracks). It must also pass a weathering test, which requires minimal color fading or chalking (formation of a white film) due to sunlight after 10 years of exposure in a Florida test location.
The most significant and widely used applied finishes for architectural aluminum are carbon-based liquid organic paint coatings, which include acrylics, polyesters, siliconized acrylics and various types of fluoropolymers. These finishes must be formulated, applied and tested to ensure they provide adequate protection against UV radiation, moisture, temperature, atmospheric pollutants and physical damage. An alternative to liquid spray-on coating is an electrostatically applied, baked-on powder coating.
To realize the full protective potential of any coating, it must have acceptable adhesion to the aluminum substrate. The metal must be properly cleaned and deoxidized, then chemically treated to convert the surface to an inert film to which the subsequent coating will firmly bond.
Such pretreatment is especially important for aluminum profiles intended for use in a seacoast environment with its corrosive humidity, salt, wind and other factors. Chromium pretreatment and an appropriate primer system have proven to be the most effective in these locations.
AAMA has developed standards that describe laboratory test methods and performance criteria for organic finishes on aluminum profiles. For aluminum profiles, these standards are AAMA 2603, 2604 and 2605, which set the criteria for basic, high-performance and superior-performance organic coatings respectively. All three 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.
Proper In-Service Care
Ken Brenden serves as technical services manager for the American Architectural Manufacturers Association.