The Semantic Metal Surface

The Semantic Metal Surface is an article which outlines the sustainable aspects of various metals. Written by L. William Zahner, the piece was originally published in the architectural quarterly, “Forward, The Architecture & Design Journal of the National Associates Committee.”

When defining a logic to use a particular surface material, various aesthetic qualities such as color, texture, patterns and boundaries are often considered. In our pursuit to arrive at materials that perform over a lifetime and do not possess hidden cost to our children’s future, considerations of manufacture and eventual recovery and recycling of the material must also play a part. Architectural metals achieve these design requirements. They are durable and lightweight. They can be formed, shaped, pierced, cut and machined in ways only plastics can attempt to copy.

Architectural metals are the family of materials that encompass aluminum alloys, copper and copper alloys, brasses and bronzes, iron and steel alloys including stainless steels, lead, tin, titanium, and zinc.

Each of these metals has a vast array of finishes and textures that add color and interface with light like no other substances on earth. Many of these metals can be coated with other metals to enhance their performance or aesthetic appeal. For example, zinc in the process of galvanizing provides tremendous benefit via galvanic protection to steel. Aluminum and steel are often painted to provide a particular color while adding a barrier to prevent the ambient conditions from affecting the base materials’ performance. In these cases, metals act simply as an affordable ductile form.

Stainless steel, titanium and to a lesser degree aluminum, are known for their unchanging surface chemistry. They react with the surrounding environment, for the most part, at a very slow rate. Their oxides develop rapidly and resist additional surface attack. Other metals, such as copper and copper alloys, zinc, and the weathering steel alloys, are left exposed to react with the surrounding environment. These metals combine with substances in the air and develop very tenacious surface oxides. These oxides enhance the appearance of the metal and provide extremely impervious barriers. The barriers are very close to inert mineral forms that are found in nature.

These inorganic surface coatings, commonly known as patinas, develop as the metal is exposed to external pollutants such as carbon dioxide, chlorine and sulfur. When you think about it, a copper roof is removing carbon dioxide and sulfur from the atmosphere and trapping it in inert mineral compounds formed on the metal surface.

The metals used in architecture will not end up in some future waste heap because of the inherent value they possess. The metal recycling business worldwide is a robust industry employing many thousands of people. No other materials used in building construction are so thoroughly recaptured and recycled for use over and over again than metals. Environmental issues surrounding the mining and concentration of metals are valid but often are taken out of context. Efforts are being made within the industry to address long term affects of metal mining and processing. Recycling of metals reduces the need for mining and reprocessing recycled materials uses significantly less energy. Aluminum recycling, for example, has become a substantial secondary business.

Reducing the ravages on the environment caused by mining, recycling bypasses the large ore refining costs. Aluminum refinement requires tremendous amounts of electricity, some 20,000 kilowatt hours per ton of aluminum refined. Most small towns use less electricity per year than aluminum refinement uses per day. The aluminum scrap recycling industry claims that recycled aluminum saves up to 80 million tons of greenhouse gas emissions per year.

The same can be said for other metals. Over 80% of the copper used to create the beautiful façade on the de Young Museum of Art in San Francisco was derived from recycled scrap metal that was recast and turned into sheet copper. Every single perforation and sheared edge left over from the process of creating the elaborate panels was collected and recycled at the fabrication facility.

Copper has an infinite recycled life. It can be used over and over again. In the event the de Young is ever dismantled, one can be certain the surface will be recycled and used on the next great museum façade. Can you say this of other building materials? There are no significant recycling efforts underway for stone, concrete, glass, fiberglass or rubber membranes. Wood and brick have levels of secondary recycling potential but not anything remotely comparable to the infinite recycling ability of aluminum, copper, steel, titanium and zinc.

Metals are available in many forms designed to take advantage of the inherent character only metals possess. Metals can be rolled into extremely thin sheets, even foils, which have directional attributes such as grain, tensile strength and ductility. Even in these thin forms, corrosion resistance is not compromised. When correctly assembled, thin skins of metal can distribute the stresses that develop from changes in the ambient conditions without affecting long-term behavior.Creating thin surfaces of metal allows for optimizing the material usage while achieving very flexible, yet durable, lightweight enclosures. This attribute of metal is the reason why aircraft and automobiles are shrouded in metal skins.

For intricate building surfaces, metals offer similar advantages over other materials. Metal roofing has long been a lightweight surfacing material that provides protection from the environment. At the same time, metal can be a significant design element used to define the building geometry and establish the aesthetic image.

Technological advances in fabrication processes have taken thin flexible sheets of metal and created stunningly intricate wall surfaces for buildings. Perforating, pressing and forming of metal provides the designer a visual and tactile interface to offer his client and the public to experience. Incorporating shape and texture is no longer a significant ‘artistic’ premium.

Thin, inexpensive surfaces of metal can enclose a building geometry and offer a lifetime of performance with little maintenance. A common means of achieving a metal surface is to assemble smaller elements known by various terms as skins, cassettes, or shingles. These thin, flexible elements allow for intricate surfaces to be enclosed without compromising the long- term performance of the metal. Each shingle acts like a scale on a fish, overlapping and engaging into the adjoining shingle. Stresses do not pass over to the next panel but are released at each edge.

To make the thin surfaces work efficiently, close attention to the edges are necessary. The edges are what the eye captures and most inconsistencies will manifest themselves at the boundaries. They can destroy the appearance, allow moisture to enter behind the metal surface, and add unnecessary clutter to the overall appearance. When skillfully executed, the edges define the surface geometry and allow for the control and distribution of stresses and moisture.

The tendency is to apply covers to overlap the edges of large sealant joints. It is cheaper, quicker and for the most part, it will deter moisture, but it will affect the aesthetic. It will require adjustment and reseal at some point and often can be less affective in performing the function of keeping air and water from entering behind the wall surface. It can be like having patches on a fine suit. One spends the money on the cloth but hires a less skillful tailor to assemble the suit.

L. William Zahner, CEO of A. Zahner Company, has worked with many of the world’s leading architects, including Frank Gehry, Antoine Predock, Herzog and de Meuron and Tadao Ando. He has contributed to a number of high profi le projects using metal as a major building material, including the Guggenheim museum in Bilbao, Spain, the Experience Music Project in Seattle and the de young Museum in San Francisco.

Notes:

• 1. Composite materials that combine metal with plastic cores are not currently recycled. Thus, when their useful life expires, they are sent to the landfill — a true waste of metal.
• 2. Recycled aluminum uses less than 4% of the energy needed in the aluminum refining process. It is predicted by the year 2020 over 30 million tons of aluminum will be from recycled scrap. This is equivalent to 18 years of primary production. Source: Recycle Scrap Industry.
• 3. Excluding copper wire which often is made from refined copper ore, over 75% of the copper used in castings, sheet, brass and bronze work is recycled. Source: Copper.org