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Sustainability 105: the new aesthetic of composite cement panels

Composite cement panels on an apartment house
Composite cement panels on an apartment house
Rendering by Rick Zimmerman

By the middle of the 20th Century, architects and builders had begun employing a variety of wall cladding panels developed with various cementitious product mixes. Unfortunately, throughout the early history of their use, asbestos fiber was often a key ingredient, due to its strengthening and fireproofing features. As recognition of the dangers of asbestosis spread, more and more manufacturers eliminated asbestos from their products. By around 1990, virtually all asbestos had been eliminated from available building products.

Due to their great versatility of size, shape, color and finish — as well as their sustainability benefits — premade cementitious panel systems have become very widely used throughout Europe as cost-effective high-performance exterior cladding. Such systems have recently begun to be increasingly used throughout the United States as well.

Most composite cement panels begin predominately as bonding compound, air and water, comprising roughly 40%, 30%, and 12% of the final product, respectively. Processing and reinforcing fibers typically add another 7%, with the remaining 11% consisting of both pigments and sealers. The primary bonding compound is locally-sourced Portland cement with limestone. While processing fibers employed to smooth the flow of production are simple cellulose (perhaps derived from recycled paper), reinforcing fibers that must bond and strengthen while flexing are most often synthetic organic fibers, like poly-vinyl-alcohol (PVA) used in the manufacture of textiles and fabrics. The nearly 1/3rd of each panel that is air is distributed among numerous microscopic pockets; these ease the strain of any water freezing, regulate moisture, and provide mini-insulating cavities.

The process of manufacture of composite cement panels is similar to that of papermaking, with a mixed slurry of raw materials being successively rolled in sheets of laminating layers to create the desire panel thickness. Though surface-applied pigments can be added to panels to achieve virtually any appearance, many manufacturers also mix pigments into the original slurry to create integrally-colored panels of greater longevity and less objectionable aging appearance. Fabricated panels are then stored for drying and curing. After drying and curing, panel sections are trimmed or cut to final size, then sealed on all outer surfaces with acrylate sealer.

There are a number of sustainable features of the most progressive panel manufacturers: a closed manufacturing cycle in which cuts and trims are returned to the source slurry; slow natural drying processes; water-based pigment systems; use of renewable energy sources for manufacture; and careful control of process-generated dust and waste.

Panel manufacturers can also offer features of benefit to the architect and builder. These include identical production batches for large projects, cutting and drilling panels for various attachments or penetrations, numbering panels to a predetermined erection or installation sequence or layout, and palletizing and sequencing panel production and shipment to suit the project progress. They may also offer design assistance in establishing panel design(s) and thickness(es) for optimal performance. The effective service life of quality composite cement panels can be 50 years or more.

Due to the ‘roller-and-flatbed’ extrusion-like production methods employed, composite cement panels can have a wide variety of applied or incorporated decoration, such as perforations or regular openings, embossed designs and patterns, textures, and even silk-screened or inkjet imagery.

As a high-density exterior cladding, a composite cement panel can typically tolerate temperatures for -40 degrees F to 176 degrees F, and has low moisture absorption and superb water resistance. Long, narrow panels can be jobsite bent to up to a 45-foot radius. Specialty castings may also be achieved at the manufacturing plant.

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