Exotic Metal Construction - Selecting the Right Material
Exotic metals help create beautiful, long lasting and durable walls and roofs. But knowing you want an unpainted metal is not enough. Selecting the right material for the individual project can have a major impact on performance.
Even for an architect who has previously specified exotic metals, selecting the right material can be a challenge. And, the product manufacturers themselves are sometimes biased toward the material they specialize in. Understanding the basics of exotic metals and knowing that consultants are available to help make those decisions, can make specifying exotic metals a breeze.
Before we go much further, let’s hammer out a few definitions. We consider exotic metals to be high performance, sustainable options like stainless steel, zinc alloy, titanium, terne coated stainless, copper and nickel-based alloys. In the context of construction, exotic metal applications are commonly roofing, wall panels, and interior and exterior trim elements, such as column covers, fascia and elevator cabs.
Metal Selection Criteria
Before selecting materials for any project, it is first necessary to define the environment in which the building will be located. Among the factors to be considered are atmospheric contaminants/pollution, the proximity to salt water and the application of deicing salts, airborne abrasives including sand, soil, and debris, ultraviolet exposure, humidity range, externally induced fire risk from airborne sparks or brush fires, and the frequency of maintenance on the part of the owner.
Stainless Steel
As a rule, stainless steel is extremely durable, and corrosion and fire resistant. It is available in a variety of grades and finish treatments. When properly specified, fabricated and installed, stainless steel will last indefinitely with little maintenance in all but the most severe environments. Stainless Steel is available in several grades and each is appropriate for specific environments.
Type 304 is sufficient for most exterior applications.
Type 316 should be used within 10 miles of saltwater bodies. However, if the building will be subjected to saltwater spray, a nobler grade of stainless steel, titanium, or nickel should be specified.
In close proximity to the use of deicing salt, even on nearby roadways where vehicle traffic can create airborne particles, Type 316 should be used. If periodic rinsing from rains will not occur on all exterior surfaces, these areas must be washed each spring. If dependable maintenance is not predicted, a nobler grade of stainless steel or titanium should be used.
Specify types 304L or 316L if welding will be employed.
Any grade, including type 430, may be used in interior applications.
Once an appropriate grade has been selected, a finish choice can be made to create the desired visual effect. An uncoated metal that will last for many years without degradation is the optimal choice. Flatness, uniformity, reflectivity and aesthetics should all be considered when choosing a finish option.
Titanium
Titanium is also extremely durable, as well as corrosion and fire resistant. When properly specified, fabricated and installed, titanium will last indefinitely in the most severe environments such as buildings subjected to saltwater spray or in close proximity to deicing salt use, and facilities that will experience little, if any cleaning and maintenance.
Grade 1 titanium, which offers a good balance between formability and strength, is suitable for most applications. However, other grades with higher mechanical properties may be considered, as design requirements warrant. With the proper grade selected, a finish should be chosen that will achieve the necessary aesthetic. Again, selecting an uncoated material that will last indefinitely without degradation will provide the best performance. Typically, titanium has a variable, grainy surface that lacks visual consistency. This may be desirable in pursuit of a random “tile” effect in building panels, in which case a mill finish should be specified. However, if uniformity is desired, a finish such as Contrarian Micro Textures’ InvariSand will provide the flattest, most visually uniform surface possible.
Sand is a non-directional, low-gloss, uniformly textured titanium finish designed for use in architectural applications. While its lower reflectivity lends itself to roofing applications, it can be applied to wall panels, coping and trim. Since InvariTech has no coatings to deteriorate, it will last indefinitely with little maintenance.
Solid Zinc Alloy
As is the case with stainless steel and titanium, pure zinc is extremely durable and corrosion resistant when properly applied. With proper specification, fabrication and installation, it will last indefinitely with little maintenance.
In general, zinc is suitable in most environments, including…
Most climates, including those where moss, algae and fungus propagation is a problem. These organisms with not survive in contact with zinc.
Marine environments not subjected to airborne sand and salt spray. However, low pitch roof conditions in a marine environment can propagate an undesirable oxide development.
Alloy 710 zinc, which contains copper and titanium, is appropriate for most applications. Other grades are also available with different mechanical properties. Finish options can change the look of the material. Untreated zinc is quite reflective in its initial state. Once installed, it takes years for the surface to mature into a dull, medium gray patina. If it is desirable to have an aged appearance upon installation, pre-weathered material that has been chemically treated to replicate years of weathering is also available. Textured, low glare zinc offers the option of natural patina development without the initial glare problem of the untreated version. Unlike copper, zinc does not produce undesirable runoff that can stain masonry and paving materials below. Since it is a natural tendency for zinc to eventually look like the pre-weathered finish, scratches will blend into the surface over time.
Zinc vs Stainless in a Corrosive Environment
Consider all of your options when selecting an exotic metal. There are many material choices and many finish options for each of those materials. However, not every option is going to be right for your project and the most convincing sales person isn’t always the best resource. Consulting a metals or corrosion specialist can help ensure the metal you choose is the right metal for the job. While manufacturers are conditioned to present their own materials exclusively, a consultant or metallurgist will offer an unbiased opinion. We are rather unique at Contrarian Metal Resources because we offer a number of high performance metals that we either manufacture or distribute. In counseling architects, we take care to mention all viable options that will meet the design requirements.
A building under construction at a coastal university is an excellent example of the right metal being critical to the project’s success and its near-miss specification. The project was originally, and appropriately, specified as a stainless steel wall and roof application. During the course of the design process a zinc material was also considered and soon replaced the stainless steel on the specification.
An exotic metal was the right choice for the project, however zinc was not. Because of the flat roof design in a coastal setting, the zinc material would lead to oxidization that would be visually undesirable. Zinc can be specified in a coastal setting if the roof features a steep slope, allowing for proper ventilation and for any corrosive elements to be washed away. This project’s flat roof is much better suited to stainless steel.
Fortunately, the project will be completed with stainless steel, providing a corrosion-free, long-lasting finish.
Zinc is unquestionably beautiful as a metal finish in its natural state but must be properly specified and installed to realize its potential sustainability.
Metal Takes Off in Airport Environments
Airports create extremely sensitive environments and present a strong need for sustainable products. But not every product is sustainable in this environment.
Every time a jet takes off, spent kerosene residue from the jet fuel punishes the nearby buildings. This residue quickly destroys coatings that would last for years in other settings. This creates the need for bare metals on airport structures.
However, not just any bare metal will satisfy this need because of glare issues. Typical bare metals are highly reflective, creating a dangerous environment for any transportation setting. Low glare metal finishes solve that problem. An uncoated metal with a low glare finish can safely and easily withstand potentially damaging airport environments. The Detroit airport expansion, JFK’s Jamaica Air Train terminal, an aviation facility in Scottsdale, AZ, and the Raleigh-Durham airport project currently under construction, all specified our non-directional, low glare InvariMatte® stainless steel finish.
Cost Considerations
Cost is an important consideration with every project. When selecting an exotic metal, some architects or owners may be weary simply because of the term “exotic.” But that need not be the case.
When we measure cost, we argue that the cost that means the most to the building owner is the life cycle cost, or the present value of all the dollars required to construct, maintain and dispose of the building over the entire ownership period. The point we make here is that exotic, high-performance metals are the least expensive material choice, on a life-cycle basis for many building applications.
The Federal Highway Administration issued a report in 2001 estimating that in the United States alone, we spend $550 billion per year combating metallic corrosion. Of that cost, $113 billion per year is spent on construction related metal failures ranging from roof perforation to replacement of components that have become aesthetically unattractive.
Aside from catastrophic damage, metallic corrosion is clearly the chief cause of metal building panel failure. When metal building panels corrode, there are undesirable consequences that go beyond cosmetics. Corroding panel systems will begin to leak, causing potentially significant damage to the interior of a building. Repair costs can be substantial, usually involving removal and replacement. Architects and contractors can save their clients money by using materials that will last the life of the building with little or no maintenance.
Life-cycle costing involves adding all of the costs of a conventional panel system, including installation and maintenance over the life of a building and comparing that figure to the present cost of a sustainable installation. As an example, a $5 million wall system replacement 20 years from now at 5.25% interest would cost $1.8 million today. This calculation suggests that it would be more beneficial to upgrade to a sustainable panel system, provided the installation cost does not increase by more than $1.8 million. When this analysis is conducted, the sustainable option usually prevails.
The price paid for an individual product is simply not enough information to evaluate its true cost. Life cycle costs, sustainability and required maintenance are all costs that should be considered because a building’s costs do not end when construction is complete. Specifying a lower cost, but inadequate product, can have far greater budget implications than specifying the correct, though initially more expensive, product.
While exotic, high performance metals like stainless steel, zinc alloy, titanium terne-coated stainless, copper and nickel alloys can seldom be justified on strip malls, for example, they offer a compelling argument for use in buildings that are designed to last longer. In most environments, metal building systems made from more common metals like galvanized steel and aluminum will require replacement within the life span of the building on which they are installed. In marine environments or northern urban locations where de-icing salts are commonly used, specifying a common metal often means more than one panel system replacement is possible over the life span of the building. However, if an appropriate exotic metal is specified that will last the life of the building without replacement, it is usually the most cost effective choice. In addition to the low life cycle cost associated with using an exotic metal, there is an environmental benefit from executing a sustainable design.
Exotic Metal Finishes
It is important to point out that the full benefit of these types of metals is typically realized by using uncoated, bare metal surfaces. There is no sense putting a coating made to last 30-years on top of a metal that will last 100 years. Since building owners demand aesthetically pleasing finishes, Contrarian Metal Resources, along with other manufacturers of high performance metals have pursued quality improvements. New finish options have pushed the aesthetics of bare metal far beyond the initial expectations of architects, designers and owners. Additionally, there has been a considerable amount of work in recent years directed to improving the quality of high performance metals to meet architectural standards. Certain finishing methods have been developed that provide excellent uniformity. With the recent availability of coil stretching, flatter sheets are now possible without incurring the expense of sheet stretching. Composite panels have also come a long way, with high performance metal versions now available that exhibit excellent flatness with the economic advantage of using inexpensive core material to stabilize the much thinner skins of more exotic metal – further reducing material costs.
The need for high performance metals of better quality is how Contrarian Metal Resources got its start. Several years ago, we identified a need to make flatter, more uniform metals available for architectural applications and created a company to do just that. We have since developed excellent rolled-in finishes, launched a domestic zinc alloy program to compete with imports, and even brought high quality metals to the domestic market from other parts of the globe.
When properly specified, exotic metals have an advantage in the marketplace. These materials deliver low cost on a life cycle basis and sustainability. A solid specification for sustainable design is about selecting a metal that will meet the criteria of the design while matching the sustainability of the building. Beauty, cost and sustainability are all advantages to metals that are specified and installed properly. The quality improvements and finish options in high performance metals have now made it possible to take advantage of the longevity of these metals without sacrificing cosmetics. The combination of these factors makes a powerful argument in favor of continued growth in the use of exotic metals in construction.
