Volume 4, Issue 8 (September 2007)
Artificial Roofing Slates and Shingles
Early in the 1980s, manufacturers started to respond to the market desires for a Class A fire-rated steep-sloped roofing material. Other manufacturers sought slate-like roofs that were lower in cost than natural slate. Both groups tried a variety of materials and cellulose fibers including fibers recovered from newsprint, bundles of wood, and more fibrous or shredded wood to reinforce portland cement matrixes. Previously, asbestos fiber was used with cement to form very durable asbestos-cement shingles, sidings, and sheets. Many manufacturers felt they could replace asbestos with other materials and did so offering performance warranties of 25 to 50 years duration. The authors have investigated and tested eleven of these artificial shakes and slates manufactured by nine manufacturers. Hundreds of roofs have been examined in more than 20 states. Some products failed before the installation was completed. Few survived past their tenth year of exposure. None of the artificial shakes and slates investigated are currently manufactured in the United States. We provide data that were generated by our laboratory tests on thousands of specimens made by nine manufacturers (A through I), identify the reinforcements present, list some of the critical properties such as flexural strength, deflection at break, and water absorption, and the specific failure modes for each product. The principal recommendation to avoid failures of this kind is to use products that have a substantial history of effective performance in the environment to which they will be used. Proceed into a market place cautiously when formulation changes are made to products with successful track records.