Considerations for anodized aluminum cladding

Specification standards

The specification terminology for anodize finishes can be complex. At its simplest, specify a Class I anodic finish to meet AAMA 611, Voluntary Specification for Anodized Architectural Aluminum, for exterior wall cladding applications. AAMA 611-20 is the most current version of this industry-accepted standard published by the Fenestration and Glazing Industry Alliance (FGIA).

To codify the specification of anodized aluminum, the Aluminum Association has designated Architectural Class I and Class II in subcategory ‘A’ for anodic coatings. These classes pertain to the minimum dry film mil thickness of the anodic coatings. Class I has a thickness of 18 µm (0.7 mil) or greater, and Class II has a thickness of 10 to 18 µm (0.4 to 0.7 mil).

Coating thickness can be measured by an ‘eddy current,’ a nondestructive test instrument, or by cutting a cross-section of the anodized aluminum, mounting it in a slide, polishing the edge, and reading the coating thickness directly with a microscope.

The Shops at Clearfork in Fort Worth, Texas, designed by Nelson Partners, includes six buildings clad in metal wall panels finished in various anodize tones. The exterior wall cladding was specified with a Class I anodic finish to meet AAMA 611. The greater mil thickness allows the anodized aluminum to withstand continuous weathering and outdoor exposure with minimal maintenance.

The Aluminum Association Designation System’s (AADS) Class I and II should not be confused with the six types and two classes of anodic coatings described in the military model specification, MIL-PRF-8625 (formerly MIL-A-8625), used primarily for non-architectural applications.

Almost all exterior architectural aluminum applications, including cladding, require a Class I specification. The greater mil thickness allows the anodized aluminum to withstand continuous weathering and outdoor exposure with minimal maintenance. Class II coating is recommended for interior applications or light exterior applications that receive regularly scheduled cleaning and maintenance.

In accordance with AAMA 611, Class I anodize also is a suitable choice for coastal climates and other salt spray conditions, including locations were salt is used to de-ice roads and sidewalks. Finishes meeting this standard possess exceptional resistance to corrosion, humidity, temperature, warping, discoloration, and wear.

Sustainability guidelines

Along with its consistent appearance and high performance, the modern acid etch anodize process also is more environmentally responsible than old, conventional, caustic etch chemistry. Since a smaller amount of the material is removed, not only less waste is sent to the landfill, but also the byproducts are recyclable. As the acid etch process takes less time, it is less resource intensive and reduces the amount of water and electric energy required. Further, emissions associated with energy production and use are also reduced.

Anodize with acid etch chemistry creates a matte finish. This also has the advantage of helping to hide small defects in secondary (recycled) billet or die lines and scratches that may occur on the aluminum’s surface.

Anodized aluminum is an inert material that is not combustible, poses no health risks, has a long life cycle, and is 100 percent recyclable. Since there is no degradation to the metal’s inherent properties and strength, anodized aluminum wall cladding can be ‘upcycled’ as future building components or other products.

More than 570 m2 (26,214 sf) of copper anodize aluminum wall panels clad Nash Women’s Center in Rocky Mount, North Carolina. An inert material, anodized aluminum poses no health risks, is not combustible, has a long life cycle, and is 100 percent recyclable.

When specifying anodized aluminum for green building projects, material ingredient disclosure and documentation is increasingly needed. Simplifying transparency and evaluation, the International Living Future Institute (ILFI) offers a publicly accessible online database of building products and materials that have earned a Declare Label. Declare screens a product’s ingredients directly against the Living Building Challenge (LBC) Red List and flags chemicals of concern.

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3 comments on “Considerations for anodized aluminum cladding”

    1. are you looking for presentations on anodizing for exterior walls, or for a particular panel system?

  1. I’ll start by saying that Linetec is a great company that willingly offers expert advice, and provides finishing services second to none. I thank Linetec (particularly Tammy Schroeder) for the many valuable articles it has provided, and for the wealth of information on its website.

    But I’ve always been puzzled by Linetec’s use of terms related to anodizing. When talking with their representatives, I often would suggest changes, but they never responded. Of course, the people who deal with clients usually can’t make changes on their own, so in June of 2010, I sent an email the vice president of sales and marketing. In it, I explained that “Anodize is a verb, it is not a noun. To anodize is to apply a protective coating. Anodizing is either a verb, ‘We are anodizing the metal’ or a gerund that is the name of the process, ‘Let’s talk about anodizing.'” I also noted other instances where Linetec’s literature or website used terms incorrectly. I don’t recall receiving a response.

    More recently, while serving on the Construction Specifier’s Editorial Advisory Board, I reviewed an article titled “Maintaining and Protecting Architectural Aluminum Finishes,” which appeared in the February 2010 issue of the Construction Specifier. In my comments, I changed “anodize” to “anodizing” in several locations, and to “anodized” in at least one location. It was interesting to see that in the published article, virtually all of my other suggestions and comments were addressed, yet the incorrect use of “anodize” remained.

    If this were an industry trend, I might care less, but I’ve looked at information about anodizing published by several other anodizing companies, and they use the terms correctly – even the oddly-named “US Anodize.”

    I know, some will say, “What’s the big deal? It’s only a word!” But in the world of specifications and construction documents, we must be consistent, and we must use defined words as they are defined. I don’t know why Linetec insists on its use of these words in their unusual way, but at least they are consistent. I can imagine a time when someone new to the company was familiar with the word “paint” – which can be either a noun or a verb – but not “anodize” – and might have thought “anodize” would be used in the same way as “paint.” I doubt that specifiers have been using “anodize” as a noun; I wonder how many cringe just a bit when they see it used that way.

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