In the United States, mechanized production of asbestos-cement shingles began in the first decades of the 20th century, following Austrian Ludwig Hatschek's invention of a process in 1900 to manufacture rolled and pressed asbestos-cement sheets. Hatschek's patent, reissued in United Stated in 1907, led to a rapid proliferation of the new shingles. One early American manufacturer, Eternit, took their company name from the title Hatschek had given his process.
Made from asbestos, an inorganic, fibrous mineral, and Portland or hydraulic cement, asbestos shingles were lightweight, economical, and fireproof. Manufacturers promoted their shingles as substitutes for traditional roofing materials such as slate, wood, and clay.
The Asbestos Shingle, Slate and Sheathing Company proclaimed in 1910: " ...these Asbestos Singles or Slates are so immeasurably superior in point of practical merit to that of any natural slating that nothing remains to be said."
A variety of shingle colors could be created by adding pigments to the wet mix before pressing or by rolling pigments onto the surfaces of shingles. Colors imitating slates, including Indian Red and Newport Gray, were common, but many other colors were available. Manufacturers assured potential customers that their shingles were colorfast. Unfortunately, many early asbestos-cement shingles faded over time, causing Columbia professor H. Vandervoort Walsh to exclaim in 1922: "For this reason we see on every hand red asbestos-shingle roofs which have bleached to sickly and thirsty pinks."
In addition to shingles, corrugated asbestos-cement sheathing, sometimes called asbestos building lumber, was produced by many manufacturers as a substitute for corrugated iron roofing. Used principally for industrial applications, corrugated asbestos could be laid directly on steel roof purlins. Industrial buildings in particular benefited from the fireproofing qualities of asbestos-cement.
Both asbestos-cement shingles--and siding--were produced into the 1980s, testimony to their popularity and affordability. The countless buildings with this roofing material also attest to the durability of the product.
Not all cementitious roofing products were asbestos-based. Concrete roofing tiles, which date from the 1840s, were produced in Germany by Adolph Kroher, a manufacturer of cement and concrete products, who developed a machine and process for pressing concrete tiles that resembled shingles. In the United States, as the concrete industry developed in the first decade of the 20th century, cast-in-place concrete roofing systems - and systems assembled with concrete slabs - evolved. The American Cement Tile Manufacturing Company, for instance, advertised "Cementile," a large (2 feet by 5 feet by 1 1/2 inches) steel-reinforced cement tile roofing, or slab, in the 1929 issue of Sweet's Architectural Catalogue. "Cementile" was offered as a flat sheet for sheathing or as an interlocking tile for a finished, watertight roof covering. Such roofing products found principal application for industrial buildings. Smaller concrete roofing tiles were available in the United States from companies such as Hawthorne in Chicago by the late1920s. Hawthorne's roofing tiles, available in no fewer than fourteen colors, simulated Spanish and French Clay tiles. Unlike asbestos-cement shingles, which were nailed in place, concrete tiles were interlocking and laid on hanger strips. Hip and ridge tiles were nailed in position and holes were then pointed with matching mortar.
Chicago-based Hawthorne Roofing Tile Company originally manufactured its tile from slabs by a hand-process. These concrete roofing tiles depicted in the 1929 Sweet's Architectural Catalog imitated French and Spanish clay tiles. They were produced with automated power-driven equipment, and the colors were impregnated on the tile surface. (Sweet's Architectural Catalogue, 1939. Courtesy of the Sweet's Group, McGraw Hill Companies, Inc.) [click image for larger view]