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Source: Asbestos-Cement Shingles, Roofing for Historic Buildings, NPS


asbestos, hazmat!!!!
Asbestos, Quebec.

The Asbestos Shingle, Slate, and Sheathing in Ambler, PA

• Facts About Asbestos [PDF file], USGS
Asbestos in Your Home, Asbestos, US EPA

Asbestos-Cement Shingles

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."

The hydraulic pressing process enabled the shingles to be given a texture, such as a rough rustic surface or one imitating weathered wood. The many styles and sizes of asbestos-cement shingles available, made possible roofs laid in various methods including American, Dutch Lap, and French (known in several variants as hexagonal, honeycomb or diamond). The French method was particularly popular for asbestos roofing, capitalizing on the economy of the material itself by laying it in an efficient manner requiring minimal overlap. Installation of asbestos shingles was similar to slate. Shingles could be punched, filed, or trimmed to size in the field by roofing contractors. Companies such as behemoth Johns-Manville and The Asbestos Shingle, Slate, and Sheathing in Ambler in Pennsylvania promoted asbestos shingles not only for new construction but also for roofing over existing roofs.

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.

What is asbestos?

Asbestos is the name for a group of naturally occurring silicate minerals that can be separated into fibers. The fibers are strong, durable, and resistant to heat and fire. They are also long, thin and flexible, so that they can even be woven into cloth.

Because of these qualities, asbestos has been used in thousands of consumer, industrial, maritime, automotive, scientific and building products. During the twentieth century, some 30 million tons of asbestos were used in industrial sites, homes, schools, shipyards and commercial buildings in the United States.

There are several types of asbestos fibers, of which three have been used for commercial applications:

Chrysotile, or white asbestos, comes mainly from Canada, and has been very widely used in the US. It is white-gray in color and found in serpentine rock.
  1. Amosite, or brown asbestos, comes from southern Africa.
  2. Crocidolite, or blue asbestos, comes from southern Africa and Australia.
  3. Amosite and crocidolite are called amphiboles. This term refers to the nature of their geologic formation.

Other asbestos fibers that have not been used commercially are tremolite, actinolite and anthophyllite, although they are sometimes contaminants in asbestos-containing products.

It should be noted that there are non-fibrous, or non-asbestiform, variants of tremolite, anthophylite and actinolite, which do not have the adverse health consequences that result from exposure to commercial forms of asbestos.

Unless the fibers are completely encapsulated, they tend to break down into a microscopic dust. A single fiber of asbestos magnified 1,000 times looks slightly larger than a strand of human hair. Because of their size and shape, asbestos fibers can remain suspended in the air for long periods of time, and therefore they can be inhaled.

Source: Kanzan Law