Stainless steel is a sustainable exterior cladding material due to its superior corrosion resistance. In addition to the environmental benefit of sustainability, stainless steel is difficult to beat on a life-cycle costing basis (in the long run, it’s cheaper than most other materials). To take advantage of stainless steel's sustainability, it is best to use it in a bare, uncoated state. This requires careful grade and finish selection to ensure good results.
II. Grade Selection
A. T316 is appropriate in most seacoast or northern climates in close proximity to the use of deicing salts.
B. T304 is appropriate in most other locations.
C. Other grades of stainless steel may be specified that are appropriate in more severe conditions. Conversely, it may be possible to use a less expensive grade in a given application. The important thing is to consult a stainless steel supplier with the requisite expertise to recommend an appropriate, cost-effective grade for your application. At Contrarian Metal Resources, we routinely make such recommendations and back them up with a 30-year limited warranty on material supplied.
III. Finish Selection
In order to determine an appropriate finish for a panel application, the following factors must be considered:
A. Glare Tolerance: Most stainless steel finishes are rather reflective. This can be a desirable attribute. However, at many site locations, such as those near airports and highways or for buildings that are out in the open, glare can be a problem. For these situations we recommend a low glare finish like InvariMatte®.
B. Degree of Pedestrian Contact: In high traffic areas, a more cleanable, fingerprint resistant finish is desirable. InvariLux™, Starlight™, InvariWeave™ and other coined textures perform well here. Some of the deeper patterns also offer a higher degree of abrasion resistance.
C. Tolerance for Variability of Appearance: Most designers and building owners want visual uniformity, particularly with a non-reactive material that does not develop a patina, like stainless steel. However, in some cases like industrial plants or smaller trim elements, a certain degree of visual variability can be tolerated. But in the majority of cases, architectural cladding systems demand highly controlled surface characteristics and superior flatness in order for the installation to look good. Some finishes, such as the rolled-in finishes produced by Contrarian Metal Resources, are very repeatable and are stretched to improve flatness. The most common problem facing specifiers of stainless steel in architecture is that the industry's decorative finishing infrastructure is dominated by #3/#4 polish that is produced to satisfy the kitchen equipment market. Architectural cladding systems require better surface uniformity and better flatness than the industry is conditioned to supply. Since this vast majority of polished stainless steel buyers are not willing to pay for architectural quality, the specifier assumes a great deal of risk when calling out "#4".
Whatever finish you choose, we believe the best value is delivered to the owner when a proprietary specification is written. This may sound counter-intuitive, but there are few competent architectural stainless steel suppliers in the world. Specifying industry standard finishes will pull the client into a range of product quality that may not be at all suitable for the project. Since cladding systems are so visually prominent, it is foolish to assume that risk. As to any concern over material pricing on a proprietary spec, it’s a matter of trust. Use a supplier you trust to help you develop a specification and put them in the documents. A reputable stainless steel company will not abuse the situation.
D. Visual Design Requirements: While this is a very important part of any project, we mention it last, because the thought process on choosing a finish as a design element should definitely include the factors mentioned above. There is a wide array of stainless steel finishes available, from low glare to a perfect mirror. New geometric patterns have been developed that create striking visual effects within the surface. When selecting a finish for a cladding application, it is important to view the finishes being considered from a greater distance than the top of your desk. From 20 feet away, the typical distance from which one might view an installed panel, some of the more subtle surface textures will disappear. Overall glare characteristics of the different stainless finishes will overcome surface textures when viewed at a distance. This is important to consider, as some deeply textured finishes are less repeatable than others, especially smoother, rolled-in finishes. There is typically an economic benefit to the smoother textures as well.
Stainless steel offers sustainability in a wide array of visual choices. Finish selection is more complicated than what looks good on your desk. To ensure good results, you should consult a stainless steel company that specializes in architectural applications. In doing so, you will have access to metallurgical expertise and if you are willing to write a proprietary specification, you will have requisite quality control on the finish you select that will meet the demands of your application.