Anodized Aluminum for Architectural Applications
Lightweight. Anodized aluminum (0.339 lb/ sq ft) weighs 60 percent less than stainless steel (1.044 lb/sq ft), brass (1.180 lb/sq ft), and copper (1.180 lb/sq ft). Anodized aluminum is also safer to handle during fabrication because of its lighter weight than other metals. It can also lower overall weight of products, reducing fuel usage, harmful emissions, and overall energy consumption.
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Anodized aluminum is significantly lighter than other metals. Chart courtesy of Lorin Industries |
Reflectance properties. Clear anodized aluminum can play a significant role in cool roof design because of its higher solar reflective index (SRI), solar reflectance, and thermal emittance than, for example, white polyvinylidene fluoride (PVDF) painted aluminum.
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Comparison of reflectance and thermal emittance properties of anodized aluminum and polyvinylidene fluoride (PVDF) paints. Table courtesy of Lorin Industries |
Testing standards comply with ASTM C1549 for total solar reflectance; ASTM C1371 for Thermal Emittance and ASTM E1980 for solar reflectance index (SRI) calculations.
Adhesive quality. While some applications require roughening of the aluminum surface for good adhesion, anodized aluminum is clean and ready for taking on adhesives without the health risks of breathing in aluminum dust particles. The aluminum oxide layer will accept adhesives without the use of a chemical treatment using hexavalent chrome. Anodized aluminum also outperforms other adhesion processes such as grit blasting and vapor degreasing.
Comparisons with Other Materials
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Anodized aluminum can be matched to simulate several other metals like antique copper and stainless steel. Photo courtesy of Lorin Industries |
Compared with PVDF paints and 316 grade stainless steel, anodized aluminum is somewhat less expensive, yet considerably less expensive than brass, natural zinc, and copper. Another advantage is that anodized aluminum weighs approximately 60 percent less than most other metals and is therefore much safer to handle during fabrication. The reduced weight also results in lower transportation costs.
Anodized aluminum has the advantage of a metallic appearance but not the disadvantage of detrimental oxidization that occurs with other natural metals. Following is a summary of the advantages and characteristics of various anodized aluminum finishes as compared to other metals:
Copper anodized aluminum. Copper is a unique metal with a distinctive look that makes it appealing for many building applications. But like other metals today, its cost is increasing and its weight and workability can complicate and add expense to the construction or manufacturing process. Copper anodized aluminum can offer the visual appeal of copper without many of its disadvantages:
• Provides a consistent, stable, and uniform color that will not stain like natural copper.
• Natural copper used in architectural structures today will eventually corrode and oxidize over time to create a green color called patina.
• Comes with a substantially lower price tag and is one-third of the weight of natural copper.
Typical architectural uses include: exterior composite or honeycomb panels, ceiling system designs, elevator panels, store fronts, retail store decoration, gutters and rain screens, and roofing systems.
Stainless anodized aluminum. Stainless steel has a clean, classic appearance, but its weight and workability can complicate and add expense to the construction or manufacturing process. Stainless anodized aluminum provides the appealing look of stainless steel plus several important advantages:
• Provides approximately 60 percent more square feet per pound than stainless steel.
• Will not show finger prints as much as stainless steel. The surface finish will not stain as easily and cleans up with only mild soap and water. No harsh chemicals are required.
• Durable, low-maintenance surface resists scratches and dents and can't chip, flake, or peel.
• Stainless anodized aluminum does not contain levels of chromium to prevent rusting, as does stainless steel. This contributes to a lower cost and avoids any potential health risk arising from the disposal of a carcinogenic substance.
• Increased production efficiency. Larger coil sizes, faster fabrication, and material that arrives clean and ready to use.
Typical architectural opportunities for stainless anodized aluminum include exterior composite and honeycomb panels, ceiling panels, column covers, elevator cab interiors, directional signs, and commercial kitchen back-splashes.
Brass anodized aluminum. One of the attractions of brass is its deep color and soft textures. Brass anodized aluminum has the same appeal plus many advantages over the natural metal:
• Provides approximately 60 percent more square feet per pound than natural brass.
• Will not tarnish or stain, unlike natural brass, which must be protected from the environment with an applied coating to prevent further oxidization.
• Since copper, a very expensive metal, is the base element found in brass (it is alloyed with a high percentage of zinc), the cost of brass is considerably higher than that of anodized aluminum.
Typical architectural uses of brass anodized aluminum include shopping mall store fronts, perforated parking garage screen panels, elevator cabs, ceiling panels, and decorative panels for interior decoration.
Zinc anodized aluminum. Long used in parts of Asia and Europe as a building envelope material, zinc has sustainability attributes and is growing in popularity in the U.S. When zinc anodized aluminum is compared with natural zinc, the former has several advantages for some applications:
• Provides 60 percent more square feet per pound than natural zinc.
• Does not scratch and burnish as easily as natural zinc and therefore has less handling and processing damage.
• Unlike natural zinc, zinc anodized aluminum will not “crack” during fabrication and bending in temperatures less than 40 degrees F.
• Natural zinc is difficult to clean, fingerprints easily, and over time will change color through environmental exposure. Zinc anodized aluminum is significantly easier to clean and will not change color in harsh environments.
Typical architectural uses include standing seam roofs, wall cladding, exterior composite and honeycomb panels, accent decorative trim, and interior decorative panels.
Paint. The anodized aluminum translucent oxide layer accentuates the rich metallic appearance of the aluminum and does not cover it up like paint. The oxide layer will not chip, flake, or peel like paint. While comparable in cost, PVDF paint does not have the benefits of anodized aluminum.
• If painted carbon steel is exposed to air and moisture, the steel will oxidize and red rust may “creep” under the coating causing the paint to peel and flake off. This is quite different from oxidization (corrosion) in steel, where red rust puffs up and flakes off, constantly exposing new metal to corrosion. Aluminum will create its own oxide layer and protect from any metal loss.
• Organic paints will chalk over time. Chalking is caused by a degradation of the resin systems at the surface of the painted finish, due predominantly to UV exposure. As the paint resin system breaks down, resin particles, along with imbedded pigment particles, lose adhesion and take on a white appearance. Anodized aluminum will not chalk.
• The aluminum oxide layer does not emit ozone depleting volatile organic compounds (VOCs) like PVDF paints.
• The anodic layer is harder than any PVDF paints on the market. In accordance with ASTM D3363, Test Method for Pencil Hardness, the aluminum oxide layer passes the maximum rating of 9H.
Composite anodized aluminum panels were used as exterior cladding for a UC Berkeley residence, Berkeley, Calif.
Photo courtesy of Westmet International