Flat: New Look for Copper Architecture Panels
Copper Applications in ArchitectureFabrication and Installation—The Details| Acknowledgements
"Metal is not flat! Not the way the architect wants it flat," said Walter J. Engert, general manager and chief engineer of General Bronze Corporation, Garden City, New York, soon after completion of the Seagram Building on New York's Park Avenue in 1959 (Figure 1).
General Bronze had fabricated and installed the building's famous bronze cladding, and Engert knew all too well that truly flat metal building panels were beyond the reach of prevailing production and fabrication methods.
At the time, the building's thousands of 1/8-in (3.2-mm) thick Muntz Metal (UNS Alloy C38000, a 60/40 brass) spandrel panels could be supplied to a flatness of only 1/4 in (6.3-mm) over their 4-ft (1.2-m) width; each one had to be belt sanded to achieve visual flatness.
Engert might have tried laminated panels, such as those used on the General Electric Company pavilion at the 1939-1940 World's Fair (Figure 2). Those panels, made from 24-ounce (0.032-in, 0.8 mm) copper and 1/2-in (13-mm) fiberboard were cross-crimped to make them appear, if not flat, then at least relatively uniform.
Over the years, architects and fabricators tried to produce flat panels using a variety of core materials and adhesives. None was entirely fault-free, suffering from such mishaps as delamination, telegraphing (imprint of core material on surfaces) and unacceptable weight.
As early as 1951, Mitsubishi Chemical Corporation had patented a continuous laminating process that firmly fixed copper (and other metals) to preheated polyethylene core material under heat and pressure. However, it wasn't until the early 1980s that the new composite panels, which combine good visual flatness, light weight, high durability, compensation for thermal expansion and practical formability became widely available in North America. The composite panels are available in widths to 62 in (1.6 m) and lengths to 24 ft (7.3 m) in finished thicknesses of 0.12, 0.16 and 0.24 in (3.0, 4.0 and 6.0 mm ). (See "Ceridian Headquarters Blends Copper With other Natural Materials for Lasting Beauty")
One major North American project incorporating copper-faced composite panels is the Ceridian Corporation headquarters building, Bloomington, Minnesota (Figure 3). Construction on the building began in 1998 and was completed in March 2000. The building was occupied in May 2000. Roughly 16,000 square feet of copper-faced composite panels form the decorative spandrel panels and column covers — dominant elements of the building's façade.
Mitsubishi's Alpolic Composite Materials Division, Norfolk, Virginia, produced the 0.16-in (4.0-mm), copper-faced (on both sides), composite panels in a single 36.5-in (927-mm) width in lengths of 10 ft; 10 ft, 2in; and 14 ft (3, 3.1 and 4.3 m). Outokumpu American Brass Company, Buffalo, New York, furnished the 12-oz/sq ft (4.1 mm thick), cold rolled copper to Alpolic in 37-in (940-mm) wide coils weighing 6,000 lb (2,721 kg) each.
The laminated composite panels were supplied with sawn edges that exhibited no displacement of the metal facings or core protrusion. Panels were readily customized using ordinary woodworking and/or metalworking tools. The composites can be routed, drilled, sawed, sheared, punched and trimmed and bend smoothly to form curves, angles or even more complex shapes.
Profiled spandrel panels and column covers were shop fabricated by Metal Specialty Systems, Incorporated, Lakeville, Minnesota. Column covers were formed from panels in appropriate widths and in either 8-ft or 10-ft (2.44 or 3.05-m) lengths. When in place, they are isolated from aluminum curtain wall framing members by perimeter, EPDM (ethylene, propylene, diene, methane polymer) compression gaskets.
The panel reveals, as well as other panel elements, were formed by mitering the metal backing of the panels (Figure 4). Ends of adjacent panels were butted together with sufficient clearance to compensate for thermal expansion and contraction within individual panel lengths. Since the panels are decorative only and do not contribute to the weather tightness of the building's envelope, no sealants or gaskets were employed in this case.
A Class 1, clear, anodized aluminum curtain wall and glazing system installed by Harmon, Inc. serves as the weathertight building envelope. The curtain wall mullions provide structural support for the decorative copper spandrel panels by means of brake formed, stainless steel sub-girts also installed by Harmon.
PVC load-bearing shims and pads isolate the copper clad composites from direct contact with the curtain wall framing system. Stainless steel anchors, clip angles, bolts and screws secure the copper spandrels to the framing system. Moisture runoff from the exposed face of the copper composite spandrel panels is directed away from the anodized aluminum curtain wall system.
At the main entrance on the building's north elevation, an aluminum-framed curtain wall system incorporates both mill finish copper composite panels and aluminum composite panels coated with a metallic pewter, custom fluoropolymer (MEGAFLON FEVE) finish (Figure 5). Then, laminated copper composite spandrel panels, which are not coated for reasons explained below, are isolated from the aluminum curtain wall framing members by means of a perimeter EPDM compression gasket.
The broad pier at the west side of the main entrance is clad with copper-faced, composite panels and provides a strong, vertical, visual element that directs attention to the principal avenue of entry to the building (Figure 6). The panels on the pier's north face are 19 in (483 mm) wide by 24 in (610 mm) high with 6-in (152-mm) deep edge returns. The panels on the pier's east face are 36 in (914 mm) wide by 24 in (610 mm) high with 2-in (51-mm) deep edge returns.
Copper-faced composite panels recessed into the limestone-faced portions of the building's north wall create belt courses that define each floor level (Figure 6). This one-foot-high belt course is repeated as the recessed central portion of the typical tripartite, copper-faced composite spandrel panels on the building's east, south and west elevations.
During fabrication and installation, the copper facings of the composite panels were protected by a strippable polyethylene film applied to the panels using a water-soluble adhesive during the final stages of the continuous laminating process. Installers wore clean, soft gloves in order to minimize finger marking and staining of the copper's bright mirror finish during panel installation when it became necessary to remove the protective film.
The author wishes to thank the following individuals who made the writing of this article possible: Loren Ahles, principal, Hammel, Green and Abrahamson, Inc.; Joe Hauglie, Ceridian Corporation; Paul Grime and Douglas Hutchison, Mitsubishi Chemical America, Inc.; Mike Challenger, Metal Specialty Systems, Inc.; Dan Welty formerly of Hannon, Inc. and Nick Glenn, The Ludlow Group.
Also in this Issue:
- Ceridian Headquarters Blends Copper With Other Natural Materials for Lasting Beauty
- Flat: New Look for Copper Architecture Panels