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Finding the Right Aluminum Finish

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Beyond buildings, Minnesota bus shelters rely on anodize to withstand harsh conditions. Photo courtesy of Duo-Gard Industries Inc.

Regardless of a project’s proximity to the ocean, transportation facilities have an added challenge of protecting their exterior-facing architectural aluminum products from corrosion. Without proper precautions and finishes, corrosion to finished aluminum components ultimately can lead to systemic failure. Such failures can produce dangerous and costly results when they affect the connecting points and places within transit and aviation centers.

Curtainwall, skylight and window framing; sunshades and canopies; column covers, rainscreens and exterior panels all commonly are manufactured from aluminum. Typically, they are integrally connected to a building’s façade and continually exposed to weathering, pollution, chemicals and abrasions.

The finish of these aluminum components not only enhances the appearance of a transportation project, but also adds protection against unsympathetic surroundings. The American Architectural Manufacturers Association (AAMA) continues to set the highest standard for architectural finishes, especially in highly corrosive environments where aviation and transit facilities often are located.

Orlando airport’s painted skylights stand up to sun and salt. Photo courtesy of Acurlite Structural Skylights Inc.

High-Performance Painted Coatings

High-performance, 70 percent polyvinylidene fluoride (PVDF) resin-based coatings for architectural aluminum products are available in nearly any conceivable color or combination of colors, while shielding against weathering, pollution and aging. These paint coatings can withstand enduring and intense UV radiation. Such attributes support long-term color and gloss retention, and chalk resistance. These highest-performing 70 percent PVDF coatings meet the most stringent exterior, architectural specification AAMA 2605, “Voluntary Specification for High Performance Organic Coatings on Architectural Extrusions and Panels.” This specification requires paint coatings to meet rigorous testing performance standards including more than 4,000 hours of heat- and humidity-resistance, and salt spray.

While salt spray performance considerations usually are reserved for coastal conditions, it’s important to remember that salt mixture frequently is used to de-ice roads, making it an equal concern in colder climates.

Designed by HKS Architects Inc., the Intermodal Terminal Facility (ITF) at the Orlando International Airport’s South Airport Complex features an 8,000-square-foot skylight. The heavy-duty, low-rise, segmented barrel vault skylight was manufactured and installed by Acurlite Structural Skylights Inc. to meet the aviation facility’s high-performance conditions.

“Although the aesthetics are certainly important, the skylight specifications are more performance driven than aesthetic,” acknowledges David Thomas, AIA, associate principal, project manager at HKS. “Firstly, we didn’t want it to leak and the skylight system needed to meet Florida product approval. The finish also needed to be able to withstand the harsh Florida climate and local airport conditions.”

Corrosion resistance was among these conditions and specification considerations for the ITF skylight’s finished aluminum framing. Hundreds of aluminum-framed segments compose the skylight system’s dimensions spanning 40.5 feet wide by 197.5 feet long. Each aluminum extrusion was manufactured with recycled content and finished in a Bright Silver color using a 70 percent PVDF resin-based coating system.

California’s Anaheim Regional Transportation Intermodal Center (ARTIC). Photo courtesy of Bess Adler, Thornton Tomasetti

High-Performance Anodize Finishes

Aviation and transportation facilities that specify Class I anodize finishes also resist the ravages of time, temperature, corrosion, humidity and warping. Anodized aluminum withstands extreme temperature changes and weather conditions, constant exposure to vehicle exhaust, and daily use by passengers. Over-sprayed salt de-icing can be managed with a simple rinsing as needed. With basic maintenance, architectural aluminum products enjoy a long life cycle.

Because it is an integral part of the substrate, the anodize process produces an oxide film that is uniform, exceptionally hard and protects the rest of the aluminum substrate from deterioration. It also provides excellent wear and abrasion resistance. The coating produced is extremely durable and the hardness of the surface is comparable to a sapphire—the second hardest substance on earth. This characteristic makes anodize an ideal choice for use in high-traffic areas where resistance properties are important.

To ensure the intended performance, Class I anodize must meet or exceed all requirements of AAMA 611, “Voluntary Specification for Anodized Architectural Aluminum.” In the most challenging applications, anodized aluminum will perform as specified and will not reduce the service life of the aluminum, but may affect the natural beauty of the surface finish. Avoid any conditions that quickly can corrode an anodize finish such as mortar, cement and other alkaline materials.

Minnesota’s first Bus Rapid Transit (BRT)—the A Line—recently added 38 shelters and 40 signage pylons engineered by Duo-Gard Industries Inc. Constructed of aluminum and finished in a Class I clear anodize, the shelters and signage offer high-traffic durability in an urban setting. Given their proximity to the roads, corrosion resistance to de-icing salts in winter and weather resistant in every season were top considerations in specifying the finish on all of the shelters.

“It was important that the design be easily replicable for future expansion, as well as easily maintainable,” says Katie Roth, project manager for Metro Transit BRT/Small Starts. “We wanted the aesthetic to convey speed of service, shown in the sleek curvature of the arched roofs. Of course, we needed weather protection and personal security, and we also wanted to maintain openness and an easy flow.”

Metro Transit owns and maintains more than 700 transit shelters throughout the Twin Cities. The A Line’s shelters are sized in small, medium and large, and are installed according to site conditions and ridership patterns. Brought to life in finished aluminum, the framing members feature narrow sightlines and maximum viewing areas.

Working with Metro Transit, Luken Architecture created the concept for the BRT shelters as part of an overall design team led by Kimley Horn and Associates Inc. More than 1,000 riders also contributed to the design by stating their preferences for improved appearance and functionality. Specifying the right finish for aluminum components on transportation and aviation facilities, not only creates a lasting impression of quality and safety for all to see.

When choosing a corrosion-resistant coating to withstand demanding conditions, remember to select either the highest-performing organic paint coating that meets the AAMA 2605 specification, or a Class I anodize that meets AAMA 611.

Tammy Schroeder, LEED Green Associate, is a senior marketing specialist at Wausau, Wis.-based Linetec, an architectural metal finishing company. With 19 years of experience in the finishing industry, she serves as an industry educator on high-quality, high-performance architectural coatings and services. These include liquid paint coatings, powder coat, anodize, thermal improvement and stretch forming for aluminum. For more information, visit, or contact Schroeder at