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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.
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]
Asbestos Cements and cementious products including some cement pipes contained asbestos fibers as a strengthening material. Asbestos cement roof ing is described just below, and cement wallboard and cement siding containing asbestos are described later in this document.
W.H. Ransom provides a succinct description of asbestos cement as it was used in roofing, siding, millboard and other products that we have annotated just slightly.
Asbestos cement is made from asbestos fibers [usually white chrysotile asbestos], ordinary Portland cement, and water [and possibly silica flour]. The cement hydrates and sets around and between the asbestos fibres which act as reinforcement.
The fibers are based on the mineral chrysolite and have an average length of around 5 mm. The relative proportions of asbestos fibre and cement used vary with the particular product to be made: for roof sheets and slates the proportion of asbestos is around 10% by weight of the dry materials. 
As we cite in detail in this adaptation from his original text, Rosato provided extensive historic detail about asbestos cement products and puts the asbestos content by weight as ranging from 10% to 75%. Typically chrysotile asbestos is the most-common form of asbestos found in asbestos-cement products.
Ransom points out that asbestos-cement materials harden with age and that the material also loses its impact strength over time through atmospheric carbonation. Thus asbestos cement roofing in particular but perhaps also siding become more brittle and more vulnerable to impact damage. We add that such roofing may also shed asbestos in roof runoff and debris.
Cracks in asbestos cement products used outdoors may also occur due to the stresses occurring as different faces (exposed and covered) are exposed to very different degrees of atmospheric carbonation and thus differential shrinkage.
However in our own experience, damage to cement asbestos roofing and siding are most pronounced where the materials were exposed to mechanical damage from ice, impact, foot traffic, and carless contractors such as renovators or cable-TV or telephone wire instsallers.
 Asbestos, its Industrial Applications, D.V. Roasato, engineering consultant, Newton MA, Reinhold Publishing Co., NY, 1959, Library of Congress Catalog No. 59-12535. We are in process of re-publishing this interesting historic text about the enormous number of asbestos-containing products and the processes used to manufacture these materials.
The following text is adapted & expanded from Rosato p. 62-66. 
Asbestos-cement products are primarily composed of Portland cement reinforced
with asbestos fibers.
The proportion of cement to fiber varies over a range of
approximately 10 to 75 per cent, by weight; it depends upon the physical
characteristics desired in the finished product. Percentage of asbestos also
can depend upon the type of manufacturing process to be used and cost of the
When compared to cement, the cost of asbestos is considered
The strong asbestos fibers behave similarly to the steel bars used in
reinforcing concrete. With the use of asbestos fiber in cement, approximately
70 to 80 per cent of the weight of nonreinforced concrete is eliminated when
roofing, siding, pipe and other similar products are manufactured.
Photo at above-left shows transite (cement asbestos) air ducts buried in a building slab. Sewer gas leaks from a failed cast iron sewer line entered this duct system. Click to enlarge any image at InspectAPedia.
Generally, most asbestos-cement products are made under pressures varying from
100 to 10,000 psi. The specific pressure generally depends upon the type of
product or process being used. This particular industry uses the greatest
quantity of asbestos. Chrysotile fiber is used principally. Some crocidolite
is used; amosite is rarely used because of its low strength.
The fibers used involve group 4 of the Canadian classification.
This grade of
chrysotile asbestos as well as groups 5 and 6 are generally classified as
medium length fiber; they are used extensively in the manufacture of such
asbestos- cement products as pipes, flat or corrugated sheets, roofing or
siding shingles, clapboard, hand molded products, and wall boards.
characteristics of asbestos-cement products are given in Table 3.1 (below).
One basic requirement for the asbestos is that it must be fully fiberized
prior to mixing it with cement in order to obtain the best properties in the
final product. It is also important to remove or minimize such impurities as
dust and grit.
In the United States, the standard grade of Portland cement is
a low-heat cement or an aluminous cement. Products are manufactured by
processes generally classified as the molding process, the dry process, the
wet press process and the wet mechanical process.
Asbestos-cement mixtures do not lend themselves readily to extrusion
processes. There has been time spent experimentally in attempting to develop
suitable processes but commercially there is little manufacturing by this
Ludwig Hatschek, an Austrian, invented the asbestos-cement shingle in 1900
which has now developed into a major commercial product. The original wet
process which was developed produced a variety of flat sheets. Later, a dry
process was developed which initially provided for competitive development
with regard to wet versus dry process. The wet mechanical process is the
principal process used today.
Asbestos-cement products lend themselves to rapid construction; therefore,
they have been particularly useful for lightweight housing and for industrial
buildings. In the last few years, approximately one-half of the asbestos used
in the United States was used for asbestos-cement sheets and pipes as well as
for floor tiles. It is reported that in 1950 approximately one billion sq ft
of asbestos-cement products for building had been produced.
TABLE 3.1. GENERAL CHARACTERISTICS OF ASBESTOS-CEMENT PRODUCTS *
Decorative asbestos-cement building products are available and conform with
modern structural and color design.
See the asbestos-cement sheeted Arched Ceiling in New York's Grand Central Station shown in Figure 3.1 below. In the case of chemical plants as well as
other plants or buildings, there exists the prime requirement
that roofing be resistant to corroding fumes.
requirement also exists in chemical transporting pipes. Durable and
fireproof roofing is obtained by the use of asbestos-cement
corrugated boards which can be installed as quickly as sheet iron or
aluminum roofing. The asbestos roof does not need paint, will not rot; it is
close to being permanent.
How to visually distinguish drywall or plasterboard from cement asbestos millboard
Above we illustrate a fragment of cement asbestos millboard that is about 1/8" thick and his hard - cementious, and at above right in our second photograph we take a look at the edges of two layers of drywall or plasterboard in an older home - showing that that material, principally made of gypsum, is comparatively soft, paper-faced, and easily cut with a knife.
On that wall the original covering was a soft wood-product fiberboard - pointed to by the tip of my pen. Wood fiberboard or paper based insulating board are not asbestos products. See SHEATHING, FIBERBOARD.
As we stated earlier, asbestos cement board is a cementious product distinguished by eye from friable and dangerous soft asbestos panels used as building fireproofing tremolite asbestos ceililng panels [image].
Research on the Asbestos Content & Hazard in Asbestos Cement or Fibre-Cement Products
TRANSITE PIPE AIR DUCT ASBESTOS RISKS includes a definition of the composition of Transite and other typical asbestos cement products. Asbestos cement products in general contain a significant percentage of chrysotile asbestos. That asbestos can be released at hazardous levels when the material is demolished, ground, sawn, chopped, or when it is badly weathered.
When that material is not exposed to damage or weathering or when its surface has been sealed (by paint for example) the level of fibre release is likely to be very low.
Excerpts: To investigate whether claims of a physical and chemical change to chrysotile fibres in a cement matrix (A/C), are valid and merit further investigation. ... When the cement is broken or crushed the chrysotile fibres are released from the
The fibres released were examined by analytical transmission electron
microscopy (TEM) to determine whether they had been altered and were no longer
identifiable as chrysotile asbestos....
Claims have been made in correspondence to HSE and in various media outlets
(Bridle and Stone, 2006), that the chrysotile asbestos in asbestos cement products is
altered, by an unexplained process, into a non-asbestos fibrous material.
being made suggest that this process is 100% efficient and no chrysotile asbestos
remains in the matrix and also no “actionable release” of airborne asbestos fibres can
The fibres found from a well-characterised asbestos cement sample showed that both
the bulk and air samples had the same morphology as a reference standard of
Many fibrils in the sample, when viewed at higher magnification, showed the
characteristic tubular structure associated with chrysotile fibrils.
Individual fibres analysed by energy dispersive X-ray (EDX) analysis showed
chemistry is similar to a reference standard of chrysotile and to published
compositions for chrysotile from various source mines around the world (when
adjusted for water content).... Only a small percentage of “coated” fibres have been observed.
HSE considers that the risk of exposure to airborne asbestos fibres is lower in asbestos
cement products compared with some other asbestos containing products due to:
- The relatively lower amount of asbestos used in this product compared to
- the hard resistant nature of the cement matrix which makes it more difficult to
release airborne fibres;
- the high use of chrysotile asbestos compared to amosite and crocidolite
This low risk factor is why the asbestos cement products can be removed without the
need to notify HSE, or the mandatory use of a licensed asbestos removal contractor.
However all asbestos containing materials are subject to the Asbestos Regulations
The external surface of an asbestos cement sheet is subject to weathering of both the
cement and the asbestos. The surface weathers at a rate largely dependent on the
cement, which may corrode at a rate of 0.02 – 0.1 mm/year in most environments
depending on the acidity of the rain and other factors. The chrysotile is more resistant
and these fibres will be preferentially exposed on the surface in some environments.
Sensitive animal tests based on intraperitoneal injection in rats have shown that there
was no reduction in the carcinogenic potency of magnesium depleted weathered
chrysotile compared to UICC chrysotile asbestos standards.
Campopiano, Antonella, Deborah Ramires, Aneta Maria Zakrzewska, Rosa Ferri, Antonio D'annibale, and Giancarlo Pizzutelli. "Risk assessment of the decay of asbestos cement roofs." Annals of occupational hygiene 53, no. 6 (2009): 627-638. Abstract:
Objectives: In an assessment of the risk of asbestos fibres release from asbestos cement materials, an important role is played by the assessment of the surface corrosion and by the disaggregation of asbestos cement. The aim of this work is to evaluate the differences among several methods used for the risk assessment that lead to a specific choice of abatement techniques.
Methods: The state of deterioration of 40 asbestos cement roofs was evaluated using two priority assessment algorithms elaborated in Italy, the ‘pull-up test’ described by the Italian Organization for Standardization and the indicators described in the Italian legislation coupled with the observation of a small sample, taken from each roof, by a stereomicroscope.
Results: The results obtained with the methods, proposed in this study, for the risk assessment of the decay of asbestos cement roofs show slight differences among them, only one deviates from the others in judgement on the state of conservation of the roof.
Conclusions: It is very important to train the operator conducting the study since a completely subjectivity-free method does not exist. Whatever method is used will always be affected by the subjectivity linked to the competency and the training of the operator.
Moreover, each method on its own cannot assess the risk of exposure to asbestos, but reliable assessment of asbestos-containing materials requires the use of more than one method, such as visual inspections, a pull-up test, and an assessment algorithm.
Nakaza, M., T. Toyama, and T. Tsunoda. "Chrysotile fiber count in asbestos-cement board plants (author's transl)." Sangyo igaku. Japanese journal of industrial health 21, no. 5 (1979): 417-421. Abstract:
An asbestos fiber counting trial has been conducted in 19 asbestos-cement board plants throughout Japan, based on the phase-contrast microscopic count on membrane filter samples. In the four working places, i.e., bag carrying-in, bag opening, board cutting and shipping, airborne chrysotile fiber counts in 1 cm3 of air, the geometric mean and standard deviation were 1.86 (1.73), 3.87 (3.01), 2.34 (2.59) and 1.26 (2.17) respectively.
Mean size distribution (geometrical length) of the fiber in bag opening and board cutting were 8.91 micrometers (sigmag 2.88) and 5.51 micrometers (sigmag 1.22) respectively by measuring on the magnified photomicrographs. As the clearing agent of filters, dimethyl phthalate with diethyl oxalate containing dissolved filter material was used.
UK HSE, Asbestos Cement & Cleaning Asbestos Cement Roofs, retrieved 2017/11/20, original source: https://www.aic.org.uk/asbestos-cement/
Excerpt: Asbestos cement is primarily a cement-based product where about 10-15% w/w of asbestos fibres are added to reinforce the cement.
U.K. HSE, Removing asbestos cement
(AC) sheets, gutters etc and
dismantling a small AC structure [PDF], retrieved 2017/11/20, original source: http://www.hse.gov.uk/pubns/guidance/a14.pdf
Continue reading at CEMENT ASBESTOS PRODUCT MANUFACTURE - a continuation of the original Rosato text as adapted and expanded, and where we discuss processes used to make various asbestos and cement based products, or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Or see Companies Producing Asbestos-Cement Products described at ASBESTOS PRODUCING COMPANIES a most-complete list of companies that produced products containing asbestos
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 Asbestos, its Industrial Applications, D.V. Roasato, engineering consultant, Newton MA, Reinhold Publishing Co., NY, 1959, Library of Congress Catalog No. 59-12535. We are in process of re-publishing this interesting text. Excerpts & adaptations are found in InspectApedia.com articles on asbestos history, production & visual identification in and on buildings.
 "Asbestos in Plastic Compositions", A.B. Cummins, Modern Plastics [un-dated, pre 1952]
 "Asbestos in Your Home," Spokane County Air Pollution Control Authority, Spokane WA 509-477-4727 www.scapa.org provides a one-page image, a .pdf file drawing of a house warning of some possible sources of asbestos in the home. The sources are not ranked according to actual risk of releasing hazardous levels of airborne asbestos fibers and the list is useful but incomplete.
 The US EPA provides a sample list of asbestos containing products epa.gov/earth1r6/6pd/asbestos/asbmatl.htm
 "Characterization of asbestos exposure among
automotive mechanics servicing and handling
asbestos-containing materials", Gary Scott Dotson, University of South Florida, 1 June 2006, web search 3/9/2012 original source: scholarcommons.usf.edu/cgi/viewcontent.cgi?article=3505&context=etd [copy on file as /hazmat/Automotive_Asbestos_Exposuret.pdf ].
 Thanks to Susan Kimball, Argus Pacific Corp., Puget Sound, WA, for pointing out that some products are permitted to contain more than 1% asbestos fibers by current standards provided that the fibers are encapsulated in an appropriate binder. Argus Pacific, in Seattle, WA 98119, 206.285.3373, is an industrial hygiene firm who also provide OSHA and DOSH regulated training in Washington State, providing classes in asbestos, lead, mold, hazardous waste, emergency response, and other occupational health, safety, and professional development topics. -- September 2008.
Work Practice for Window Removal and Window Putty Patching
With Less Than Or Equal To 1% Asbestos Window Putty and Caulking" University of Washington, 2002 http://www.washington.edu/admin/asbestos/1putty.html
 How do I Manage Asbestos in our House or Apartment Building?, Illinois Department of Environmental Conservation, provides this article at http://www.epa.state.il.us/small-business/asbestos-in-home/
 "Asbestos Awareness Training Outline", Michigan Department of Licensing and Regulatory Affairs, Michigan Occupational Safety & Health Administration, Construction Safety & Health Administration - asbestos program, Michigan Department of Licensing and Regulatory Affairs
Michigan Occupational Safety & Health Administration
Construction Safety and Health Division
7150 Harris Drive, P.O. Box 30671
Lansing, Michigan 48909-8171
Phone: 517.322.1320, Fax: 517.322.1713
E-mail: firstname.lastname@example.org, web search 3/9/12, original source www.michigan.gov/ [copy on file as /hazmat/Asbestos_awareness_training.pdf ]
 Damian Murphy, Marin OHS&E Consulting,Mairin OHS&E Consulting Pty Ltd
18-20 Kirk Street
Moe Vic 3825
P: 03 5127 2311
F: 03 5127 2399
E: email@example.com, personal correspondence to Daniel Friedman. 3/12/2013 Website: www.mairin.net.au
 Asbestos in buildings - employee notice, University of Washington dept. of Environmental Safety, http://www.ehs.washington.edu/ohsasbestos/index.shtm
 Window putty to be exempted from asbestos removal by State of Maine - http://list.uvm.edu/cgi-bin/wa?A2=SAFETY;wYpdKg;20010307113643-0500A
 EPA Region 6 identifies window putty as asbestos containing - http://www.epa.gov/earth1r6/6pd/asbestos/asbmatl.htm
June 1997 - Window Putty - OSHA case cites contractor for asbestos exposure during removal of window putty http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=NEWS_RELEASES&p_id=1091
 Asbestos Identification and Testing References
Asbestos Identification, Walter C.McCrone, McCrone Research Institute, Chicago, IL.1987 ISBN 0-904962-11-3. Dr. McCrone literally "wrote the book" on asbestos identification procedures which formed
the basis for current work by asbestos identification laboratories.
Stanton, .F., et al., National Bureau of Standards Special Publication 506: 143-151
Pott, F., Staub-Reinhalf Luft 38, 486-490 (1978) cited by McCrone
 EM>ASBESTOS IN YOUR HOME U.S. EPA, Exposure Evaluation Division, Office of Toxic Substances, Office of Pesticides and Toxic Substances, U.S. Environmental Protection Agency, Washington,D.C. 20460
"Handling Asbestos-Containing roofing material - an update", Carl Good, NRCA Associate Executive Director, Professional Roofing, February 1992, p. 38-43
 EPA Guidance for Controlling Asbestos-Containing Materials in buildings, NIAST, National Institute on Abatement Sciences & Technology, [republishing EPA public documents] 1985 ed., Exposure Evaluation Division, Office of Toxic Substances, Office of Pesticides and Toxic Substances, U.S. Environmental Protection Agency, Washington,D.C. 20460
 Asbestos products and their history and use in various building materials such as asphalt and vinyl flooring includes discussion which draws on ASBESTOS, ITS INDUSTRIAL APPLICATIONS, ROSATO 1959, D.V. Rosato, engineering consultant, Newton, MA, Reinhold Publishing, 1959 Library of Congress Catalog Card No.: 59-12535 (out of print, text and images available at InspectAPedia.com).
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The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
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