How Zinc Plating Enhances Architectural Elements
Electroplating metal architectural/structural elements with zinc both protects them against corrosion and adds to their aesthetic appeal
Metal architectural structures are designed to be both functional and aesthetically appealing. Electroplating elements of those structures with a zinc coating can contribute significantly to the success of both goals. The fundamental purpose of plating is to protect the metal against corrosion that can affect the strength of structural elements. But plating is also a valuable technique to enhance the visual appeal of decorative metal surfaces in both interior and exterior settings.
It is this blend of capabilities that has made zinc electroplating structural and decorative elements popular with many architects.
Electroplated zinc plating provides a metal structural component with a clear, thin coating (approximately 5-25 microns) that protects the underlying surface without interfering with its functionality or its decorative features. This contrasts with thicker (100-150 micron) coatings applied by hot-dip galvanizing, which can fill in threads and holes and blur the appearance of decorative features. The process of hot-dip galvanizing also involves high heat, which can warp long metal structural items and even large steel panels.
In addition, zinc plating provides a “sacrificial coating.” This means that, if the plating is later scratched—even to the depth that the underlying bare metal is exposed—the surrounding zinc coating will “sacrifice” itself and continue to protect the exposed metal from corrosion. This level of protection can give interior decorative elements like wall panels, tabletops and bars a longer useful and attractive life.
In outdoor settings, standard zinc plating tends to weather and corrode, but still protect. If a weathered look is not the desired goal for a project, a zinc-nickel alloy plating will provide even greater protection—up to 10 times that of zinc alone—giving steel structures a longer corrosion-free working life comparable to the protection offered by hot-dip galvanizing, but without the thick coating and potential for warping.
Though most regularly used with carbon steel, zinc plating works equally well to protect other metals, including brass and copper. In our experience, however, many architects prefer to let brass shine unplated and want copper to oxidize.
But beyond its ability to protect metals, a less-recognized benefit of zinc plating is its ability to alter the surface appearance of a metal element to enhance its aesthetic appeal. The subtle unevenness of surface color that zinc plating produces on larger metal panels, for example, gives the surface a somewhat industrial look, enhancing an industrial chic design. Architects we have worked with have used this look to create eye-catching storefronts and interior wall surfaces in restaurants, retail spaces and offices.
In addition to the standard clear zinc plating, plating can also produce coatings in black, iridescent and olive drab. This is possible because zinc plating is a two-step process. A clear chromate finish is traditionally applied to further reduce the corrosion of the zinc plating. This can be replaced by a yellow hexavalent chromate that results in an iridescent surface finish, a black chromate that produces a black appearance, or an olive drab chromate that results in a military look.
In one project, for example, such industrial-look panels were combined with unfinished wood slabs to create vintage-looking countertops and a bar in a restaurant. In another, large polished steel panels were coated with yellow hexavalent chromate to form a dramatic iridescent wall.
Preparing for Plating
For those less familiar with electroplating and the finishes and protections its processes can provide, it is essential to consult with a knowledgeable plater. Some effects may not be achievable with plating but may be possible with other processes. Powder coating, for example, will be more effective for outdoor installations like playground equipment or park benches, especially when zinc plating is used as the base coating, and the plater should guide the architect in that direction. On the other hand, the plater will also likely be familiar with techniques and potential results that the architect is not familiar with. Cooperation between architect and plater is essential for achieving the desired result.
Also, not all platers are equal in terms of their capabilities. Can the plater you are considering plate a large wall installation in one piece, for instance, or would it have to be done in sections, necessitating welds or other joints that might affect the finished appearance? Is the plater capable of applying the chromates needed to produce the finish color you would like?
Lastly, the architect should consult with the plater to ensure that the metal elements he provides for plating meet the plater’s needs. A large panel, for example, will have to include holes that will enable the plater to hold it securely while manipulating it in and out of the plating bath. Any element that includes closed shapes or any tubular elements that may trap plating solution must have drain holes. If the project is an installation with multiple parts, the plater must be able to plate those parts in the same batch to ensure a consistent look.
If this sounds like a complex process, it is if the result is to be successful. But communication between the architect and the plater before the plating, so that each party understands what the other is capable of, can make the process a simple and mutually beneficial one.
George Gatto Jr. is president of Gatto Industrial Platers Inc. in Chicago. To learn more, visit www.gattoplaters.com.