Collapsing building © Daniel Friedman Asbestos cement products
asbestos cement roofing, siding & millboard composition, history, production, uses, identification & safety

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Asbestos cement sheet product production, properties, & uses: this article describes asbestos cement sheet materials including asbestos roofing tiles or shingles, asbestos-cement shingle siding, flat asbestos-cement sheet products such as asbestos millboard and asbestos insulation, and corrugated asbestos sheeting used for both roofing and siding.

Cement asbestos materials: this article series describes asbestos cement products & materials and the history of their production and use. This article includes text & data Adapted from Rosato (1959 out of print) on the production and use of asbestos-containing materials, adding photographs, inspection, repair and maintenance advice, and updates on asbestos hazards involved in the installation, repair, or demolition of asbestos cement products such as roofing and siding or asbestos millboard that remain in place on buildings.

Our page top photograph shows badly broken cement asbestos roofing shingles on a building in upstate New York.

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Asbestos Cement Sheet Products

Cement asbestos roof shingles (C) Daniel Friedman

The following text is adapted & expanded from Rosato p. 75-78 [1] © 2013

Asbestos is safe and legal to remain in homes or public buildings as long as the asbestos materials are in good condition and the asbestos can not be released into the air. - US EPA

[Click to enlarge any image]

The major production of asbestos-cement materials is in the form of shingles and sheets. The principal products, in order of their volume,* are siding shingles, flat sheets, roofing shingles, and corrugated sheets. Flat sheets and cor-rugated sheets are utilized for interiors as well as exteriors.

The oldest use of asbestos-cement products involves the use of fire-proof roofing shingles.

Additional products manu-factured are simulated ceramic bathroom tile, facings of acoustical materials, electrical switchboard panels, laboratory table tops, electrical conduits, electrical sheets, and others.

Asbestos-cement sheets are made either in the dry or wet mixing process.

Manufacture of Asbestos Cement Siding Shingles.

Asbestos wall siding (C) Daniel FriedmanAsbestos-cement siding is being used in millions of homes, inasmuch as it is both attractive and 'serviceable. Sidings are presently available with improved weather-resistance and with distinctive surface texture or color. They have been accepted widely for exterior use in new homes of all price groups.

* The Asbestos-Cement Products Guide, New York, Asbestos-Cement Products Association.

** "Advanced Designing with Asbestos Siding," New York Asbestos-Cement Products Assoc.

The colors are permanently embedded throughout the sheet. They will not powder or peel off. Different methods to improve the weather resistance of siding have been de-veloped.

They are used in the dry process. Sodium silicates are one of the materials used for this purpose. Originally, they were not successful since they were only insoluble after baking at temperatures higher than 900°F.

This tempera-ture condition is detrimental to the cement base. A combina-tion of sodium silicate and sodium fluoborate becomes stable when heated at 500°F for 1/9 hr. After the reaction has occurred, an insoluble semi-gloss finish is produced. To pro-duce approximately one ton of material, 48 lb of sodium silicate and 6 lb of sodium fluoborate can be used with 16 lb of water and 18 lb of iron oxide pigment.

Silicone resins have been developed for use with asbestos-cement shingles to provide for a water repellent structure. One example involves coating a silicone composition on shingles to make them water repellent and bloom resistant.

Asbestos Cement Siding: some building siding materials contain asbestos: Cement-asbestos siding shingles (photo at left) (non-asbestos-containing replacement products now available) and cement asbestos board siding as well as undersheeting.

This is a cementious material and is unlikely to release significant levels of airborne asbestos fibers unless during severe demolition activities or someone using a power saw or sander on the material.

See ASBESTOS CEMENT SIDING for more details about cement asbestos building siding, its repair, removal, demolition, or cover-over.

Manufacture of Asbestos Cement Roofing Shingles

Cement asbestos roof shingles (C) Daniel FriedmanAsbestos-cement roofing shingles provide for permanent and decorative structures.

The weather resistant and fire resistant characteristics of shingles make them desirable for both industrial and home applications.

They provide for one of the light, weight-high strength roof-ing materials.

They are available in colors which range from light pastels to deep tones and include both white and black.

Some shingles are designed in solid colors, while others pro-vide a blended color effect..

Painting is not needed to pre-serve shingles but if a change in color is desired, they can be painted.

Properties & Manufacture of Asbestos Cement Flat Sheets & Asbestos Millboard

Asbestos millboard (C) Daniel FriedmanAsbestos-cement flat sheets were at one time manufactured only in the typical gray color of cement and usually only accepted for industrial purposes. However, they are now available in such a variety of colors and surface finishes that their usefulness has been greatly expanded.

Chrysotile asbestos is thge principal source for these products.

* Philadelphia Quartz Co.. 32, No. 6, P and Q, Philadelphia, Penna.
** Union Carbide Corp., American Patent 2, 833. 673 (May 6. 1958).

Sheets are available with smooth surfaces; they are waxed or lacquered with a variety of colors for use as office parti-tion walls, kitchen walls, table tops, acoustical panels, elec-trical sheets, building corridors; they are used generally where ease of cleaning is important.

Flat sheets are used both internally and externally. Ex-terior sheets are made so that they resist outdoor weather. They are impervious to water; they prevent the entrap-ment of moisture within the building walls, a situation which would normally cause the decay of wood. Decorative sheets can be used for table tops to provide chemical resist-ant surfaces.

Complete asbestos-cement boards or flat sheets are used; however, combinations incorporate asbestos-cement in sand-wich structures. "Transitop" * is a typical composition board consisting of an integrally impregnated insulating board core, faced on both sides with asbestos-cement board. Waterproof adhesive is used to laminate the insulating core as well as to bond the noncombustible asbestos-cement faces to the core.

This combination of materials provides for structural strength, high insulation values and maintenance-free interior and exterior finish in a single fire-resistant panel. See Table 3.2. It is suitable for indoor or outdoor use. The wood fiber insulating core is integrally impregnated to provide maximum strength and a highly resistant barrier to moisture without appreciably affecting the insulating properties.

The conductivity of the core complies with Federal Specification LL.L-F-321h-Class A. The sheet products are also used where electrical requirements exist. Examples of electrical applications are provided by Canadian Specifications; Spec. 34-GP-8 pertains to asbestos-cement electrical conduit.

Asbestos Cement board used as a "fire proofing" over and near boilers and wood stoves - also called "cement wallboard" and "asbestos millboard".

Note that asbestos cement board is a hard cementious product easily distinguished by eye from more friable and dangerous soft asbestos panels used as building fireproofing such as these almost pure tremolite asbestos ceililng panels. More about this building can be read

Asbestos millboard (photo at above left) used for stoves and heaters, in garages, as fireproof wallboard, as gaskets, as washers in electrical applications, stove mats, safes, motion picture booths, automobile hoods. Asbestos millboard is a cementious product that was produced in sheets and used for fire barriers and in other applications.

The material is quite similar to cement asbestos roof shingles and siding, and was produced in sheets of varying thickness (typically 1/8"- 1/4") and dimension depending on its intended use.

Asbestos millboard was used as a fire barrier behind and over and around wood stoves, coal stoves, & heating appliances in buildings up to 1978. It was also used in some locations where a moisture-resistant building material was desire.

Also see Asbestos cement flat sheets.

* Johns-Manville Corp.

Rosato detailed the production of asbestos millboard. He described asbestos millboard as a "heat insulation" product, an apellation with which we disagree. Because of its dense and cementious nature asbestos millboard, while fireproof, can conduct heat towards combustible materials that it might cover, such as wood framing. Without an adequate air space or other insulation, heat conducted through non-combustible materials can still result in a fire. (Rosato 1959, 100-102)

Details about how asbestos cement board or millboard was produced are at ASBESTOS MILLBOARD PRODUCTION

Perforated asbestos-cement

Perforated cement-asbestos sheets are manufactured with sound absorbing elements. These particular sheets are used in broadcasting studios, music rooms, and auditoriums where specific resistance to fire and moisture exists. Federal Spec- ifications SS-A-118b, Type 2a and Class A are applicable.


(Units expressed in Btu/sq ft/ ° F/hr)

Overall thickness 11/16 in. 1 1/8 in. 1 9/16 in. 2 in.
Core thickness 7/16 in. 7/8 in. 1 5/16 in. 1 3/4 in.
Approximate wt, uncrated, lb/sq.ft. 3.2 3.9 4.6 5.3
Conductance of iimpregnated insulating core 0.78 0.39 0.26 0.19
Transitop wall coefficients air to air ("U") value
Inside walls and partitions
Outside walls




Transitop surface to surface coefficients, conductance



* Johns-Manville corp.

Manufacture of Asbestos Cement Corrugated Sheets.

Corrugated asbestos cement roofing as installed and aged (C) InspectApedia Daniel FriedmanAsbestos-cement corrugated sheets are generally only produced in the color gray.

Their principal use has been for industrial walls and roofs where corrosion resistance is important. In recent years, this type product has been incorporated in farm buildings, commercial in-teriors and home exteriors. Its principal use on the farm is based on fire safety, strength and resistance to rats and termites.

Our photo, left, shows typical corrugated asbestos cement roofing installed. The dark areas are probably algae and the light reddish-brown areas may be a form of lichens.

Details and more photos of corrugated cement asbestos products are found

Asbestos, Its Industrial Applications - Rosato: Text & Chapter Index [1]


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