{"id":44866,"date":"2017-09-29T15:20:55","date_gmt":"2017-09-29T19:20:55","guid":{"rendered":"https:\/\/www.constructionspecifier.com\/?p=44866"},"modified":"2017-09-29T15:20:55","modified_gmt":"2017-09-29T19:20:55","slug":"think-zinc-designing-specifying-longevity","status":"publish","type":"post","link":"https:\/\/www.constructionspecifier.com\/think-zinc-designing-specifying-longevity\/","title":{"rendered":"Think Zinc: Designing and specifying for longevity"},"content":{"rendered":"
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All photos courtesy RHEINZINK America and Sheet Metal Supply Ltd.<\/span><\/em><\/span><\/figcaption><\/figure>\n

by Ben Kweton, CSI-EP
\n<\/strong>With natural roof and fa\u00e7ade metal materials that have been in use for centuries, importance should be placed on specifying a material not solely for its longevity, but also with an understanding of its long-term aesthetic potential (and pitfalls). Just as we do not plant saplings without the idea of them one day growing into trees, zinc cannot be specified without an appreciation for the patina and aging process. The material is long-lasting, lends itself to unique detailing, and is amazingly versatile, but an understanding of the maturation process manages client expectations and allows a specification to leave a legacy long after the project is complete.<\/p>\n

Architectural zinc has enjoyed a successful history of European application for almost three centuries and increasing popularity in North America since the early \u201990s. As an alloy primarily comprising of zinc with additional controlled amounts of titanium and copper, the material provides a unique, low-maintenance aesthetic at an extremely low amortized lifetime cost.<\/p>\n

Freshly produced natural \u2018bright-rolled\u2019 zinc will have a shiny silver appearance and a smooth finish. Without any applied protective organic coatings, it will also be the surface condition that begins the patina process the fastest. Bright-rolled zinc is the material on which most other \u2018weathered\u2019 products are based. Without the head start of a secondary patination process, natural zinc can be expected to slowly weather to a matte-gray patina. The duration of this process depends on environmental and building conditions, with the greatest predictor of final appearance being the observation of local in-situ projects that have been through several years of exposure.<\/p>\n

Common surface patina is achieved through the formation of first zinc hydroxide or Zn(OH)2<\/sub>, then zinc carbonate (ZnCO3<\/sub>). Both of these compounds not only add to the aesthetic appearance of the product, but also protect the material and increase its longevity.<\/p>\n

In marine environments, zinc, combined with salt in the air, will form zinc oxychloride (Zn2<\/sub>OCl2<\/sub>) on the surface. In an age where most people lack the patience and foresight to enjoy the natural process of patination, there are several methods\u00a0 of producing zinc with a more aged appearance.\u00a0 The three main sources for these enhanced surface conditions are phosphating, pigmentation, and a natural pickling process.<\/p>\n

The phosphating process deposits a phosphate-crystal coating onto the natural zinc alloy. The duration of the phosphate process and thickness of the coating determine the finished color range and luminance. Thus, this method produces a zinc coating rather than a head start on the natural patina process. Any scratching or scuffing will reveal the underlying alloy and start to weather naturally, potentially causing aesthetic concerns. Through the life of a phosphate product, the alloy is expected to eventually develop its natural patina compounds and force the phosphate coating to give way.<\/p>\n

Tinted products can be produced in a multitude of colors and are typically applied over natural bright-rolled or phosphate zinc. The initial appearance usually preserves the initial random and natural texture of zinc and these coatings. Just as with the phosphate surface aspect, the pigments can be expected to fade and the natural patina of zinc to overtake the initial appearance. Exposure, slope, environment, and wetting and drying cycles all play a part in determining how long this process will take.<\/p>\n

Lastly, a weathered look can be achieved through a pickling process, where the alloy is etched in an acid bath to achieve either a natural blue-gray or graphite-gray appearance. It is important to note in the case of pickling, the process is actually bringing out the natural patina formation, and two separate alloys are responsible for the different shades (blue-gray and graphite-gray).<\/p>\n

After long-term weathering, the materials will remain lighter and darker by comparison. The initial appearance of these surfaces tends to have a subtle directional grain running lengthwise through the material, though this grain will dissipate as the patina develops. Should either of these surfaces be scuffed or scratched, the self-healing properties of the alloy will restore the surface through repatination, eventually matching the surrounding metal and becoming unnoticeable. The healing process is a distinct advantage over phosphate and tinted products that use a single alloy.<\/p>\n

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Either as a complementary accent or the primary fa\u00e7ade, zinc integrates well with an extensive palette of materials.<\/span><\/figcaption><\/figure>\n

Design considerations
\n<\/strong>While it is exciting to get the photography team and drone pilots out right after the landscaping is done and the ribbon cutting is happening, design\/construction professionals also need to consider the potential life cycle of zinc can go well past a century on wall applications, and 80 to 100 years on a roofing application. Though it is difficult to extrapolate what the aesthetic will be into the next decade\u2014much less the next century\u2014some considerations should be taken past the initial display of material samples.<\/p>\n

The very best predictor of long-term surface appearance is to physically observe a zinc project that has had the opportunity to weather. Most, if not all, zinc manufacturers keep a running list of projects based on type of project, specific material, and locale, and make this available to any interested parties. It is important to note how long a project has been in place and how the weathering process has changed the tone and texture of the surface in relation to initial samples, and equally critical to address any questions or concerns directly with the manufacturer, representative, supplier, or installer.<\/p>\n

Exposure plays a very important role in the patination process. A slightly pitched roof weathers more quickly than a steeply pitched roof, which weathers more quickly than a fa\u00e7ade. For this reason, tinted or pigmented zinc is typically not used on roofing applications. The only way to achieve a long-term appearance darker than the matte pewter gray patina is by using a separate alloy specifically designed to weather and maintain a darker appearance through its life cycle.<\/p>\n

Consistent and uniform weathering can be a greater challenge in a fa\u00e7ade application. Though the same factors apply, walls often receive less exposure to wetting and drying cycles from protective overhangs. Though patination of zinc in a fa\u00e7ade application will take much longer to weather uniformly, it is reasonable to expect that it will happen eventually. The speed at which a project weathers into the natural patina is highly dependent on its microclimate.<\/p>\n

Zinc manufacturers do their best to mitigate tonal variation from batch to batch. Tonal variation occurs naturally and may be found within the same coil or sheet. Since the material is not painted, it exhibits the natural colors of the constituent elements. This is part of the beauty of the product\u2014it is not a cause for rejection.<\/p>\n

Further, zinc can be expected to perform and last very well in marine environments. As mentioned previously, the patina is formed as a different compound, but zinc can also react with the salt air to form a water-soluble white zinc chloride crystal. This is not adhesive by nature and is typically washed off through rainfall or even an occasional washing to maintain the desired appearance. Again, even in a marine environment, there is a reasonable expectation of an 80- to 100-year life cycle with proper design and installation, depending on exposure.<\/p>\n\n\n\n\n
OIL-CANNING<\/strong><\/span><\/td>\n<\/tr>\n
Oil-canning, or perceived waviness in the pan of the panels, is the skeleton in the closet for the architectural metal community. Even perfectly installed roofs and walls will exhibit this phenomenon to some degree, and poor installations only serve to exacerbate the situation. Unfortunately, there is no magic-bullet solution to the issue, though it is possible to put a little lipstick on the pig and help ameliorate the situation with the following suggestions.<\/p>\n
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  1. Be sure to start with the flattest surface possible\u2014plumb, square, and level. Metal, including zinc, cannot be used to cover up poor carpentry.<\/li>\n
  2. Consider making panels out of thicker material. Most fabricators can run panels up to 1.0-mm (0.04-in.) zinc, though installers will have a harder time performing more intricate details.<\/li>\n
  3. Natural\/bright-rolled zinc with a high initial gloss will show more oil-canning than a preweathered product.<\/li>\n
  4. Panel width can be reduced to lessen the size of an unbroken plane, or striations\/ribs can be added to the panel pan.<\/li>\n<\/ol>\n

    Oil-canning is never a cause for material rejection, but should be explained and managed prior to fabrication and installation. The manufacturer, fabricator, and installer may all have valid suggestions on how to make the project look as good as possible.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

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    Interior applications for zinc panels continue to be popular as architects seek ways to relate the exterior fa\u00e7ade to interior design.<\/span><\/figcaption><\/figure>\n

    Proper detailing
    \n<\/strong>Zinc, like any other metal roof and fa\u00e7ade skin, is best treated as a water-shedding or rainscreen system, working in conjunction with weather barriers to achieve highly functional, long-term solutions. Each zinc manufacturer can provide guidance as to proper detailing. Some key points include the following:<\/p>\n