What You Should Know About Asbestos-Cement Siding

Cement-Asbestos Siding Tiles
Cement-Asbestos Siding Tiles. GeoStock / Getty Images

Learning that a home's siding contains asbestos can lead many homeowners to a panicked fear that this siding must be removed immediately. The health risks of asbestos are well known, and we are well advised to exercise caution when it comes to any building material that contains asbestos. But in reality, removal of siding containing asbestos should be approached very cautiously. If left alone, asbestos- cement siding and other building products containing asbestos can be fairly benign. It is when these materials are disturbed through sawing, sanding ripping or demolition that the fibers become mobilized and can pose a health risk if they are inhaled or otherwise ingested. If such materials are removed, extreme caution and special techniques are required, and the better strategy is usually to leave them in place or cover them up. 

The Health Risks of Asbestos

There is no question that asbestos fibers do pose a health risk, and this is the reason that building materials no longer include this material. Asbestos is a naturally occurring silicate mineral that can be pulled into a fibrous material that is extremely resistant to heat and fire, and which has good insulating properties. Up until the early 1970s, asbestos was found in many building materials, thanks to these virtues.

The health risks of asbestos have been known for many years, since the early 1960s. Inhaled asbestos fibers have definitively been linked to a variety of lung diseases, including asbestosis and different types of cancer, such as mesothelioma. No level of exposure to asbestos is deemed safe, although the people suffering from serious asbestos-related diseases are usually those who have handled the material regularly in jobs related to the manufacture and installation of asbestos and materials containing it. There are, however, documented instances of family members developing diseases simply by exposure to asbestos fibers carried home on the clothing of workers.

A Brief History of Asbestos-Cement Siding

Asbestos-cement is a mixture of Portland cement reinforced with asbestos fibers. The Portland cement binds asbestos fibers into a hard mass. Asbestos cement was first developed in 1905 by the Johns-Manville company, who became one of the premier manufacturers of cement-asbestos materials. Siding material and other products using asbestos-reinforced concrete continued to be sold and installed well into the early 1970s, since it was believed that the process of making asbestos cement somehow neutralized the asbestos fibers. This was later shown to be false, when it was demonstrated that asbestos-cement materials could also release asbestos fibers in their pure form when the materials were crushed, broken, or otherwise pulverized. But asbestos-cement was not only commonly used, but was a recommended siding material from the 1940s to the 1960s, thanks to its fireproof nature.

Advantages and Disadvantages Asbestos-Cement Siding

The presence of asbestos cement siding should not necessarily be viewed as ​a serious problem. There are hundreds of thousands of homes and garages with this siding material, and when it is in good shape, the health hazards are minimal. The presence of asbestos-cement siding, in and of itself, is not a serious drawback. The National Association of Certified Home Inspectors notes the following advantages and disadvantages of asbestos-cement siding: 

Advantages

  • Asbestos cement siding is highly fire-resistant and will not burn or melt the way vinyl and wood siding will.
  • It resists termite damage.
  • It resists rotting.
  • It has been manufactured with textures intended to simulate the look of other cladding materials, such as wood grain.
  • It is fairly easy to clean and maintain.
  • Unlike more porous siding materials, such as wood clapboard, asbestos cement siding will not quickly soak up paint, which allows it to be painted more easily.

Disadvantages

  • Asbestos cement siding is very brittle and can be easily chipped, cracked or broken.    
  • The use of a pressure washer for maintenance can crack the siding and lead to moisture intrusion, if the pressure setting is high enough.
  • Asbestos cement can be dangerous if pulverized by sawing, sanding, breaking, etc.
  • It is difficult to find replacement siding for repairs.
  • This product cannot be refurbished, unlike other forms of siding.  Wood clapboard, for example, can be sanded and re-painted, and cedar shake siding can be sand-blasted and re-stained.  Either of these methods can restore wood close to its original state.  But this is not possible with asbestos-cement siding.
  • It is no longer considered aesthetically desirable.

Why Removal Should Be Avoided

Despite some inherent advantages to asbestos-cement siding, and despite the inherent dangers of disturbing it through removal, some homeowners insist on removing it. But this should be carefully considered. A better strategy may be to cover it over with new siding, which effectively seals in the asbestos material. This is usually the preferred method of dealing with asbestos building materials. Most siding companies are well-experienced at techniques for covering over existing asbestos-cement siding with new vinyl, aluminum, or a newer form of fiber-cement siding. If a siding company removes an outer layer of siding and finds an older layer of asbestos-cement siding beneath, the standard procedure is simply to cover it over with new siding rather than remove it. 

Removing the asbestos-cement siding, in addition to the health hazards involved, only adds more work to your project and will cost that much more. Removal of existing siding is not part of most siding companies' estimates. Even if they do agree to do this, it will be an added cost and the company will most likely contract out the job to a demolition company specializing in asbestos removal.

Keep in mind that removing asbestos cement siding is not a simple matter of calling up a local contractor. Depending on your locality, chances are good that you'll need to obtain special permits and have a special asbestos abatement company perform the work. Such work can be done by a homeowner, but special procedures and disposal methods must be followed. 

A home that has enclosed the old asbestos-cement siding with new siding is perfectly acceptable to home inspectors and real estate assessors, and it rarely has any negative effect on home values. 

Bottom Line

Keep these points in mind if you are worried about asbestos-cement siding:

  • Homes built between 1920 and the 60s are likely to contain asbestos in any cementitious siding tiles.
  • Cementitious siding installed after 1973 is very unlikely to contain asbestos. These materials are known as fiber-cement siding, and they contain no asbestos. 
  • Cement-asbestos siding tiles do not need to be removed simply because they contain asbestos. There is no legal requirement to do so, nor is there significant real estate benefit. 
  • Cutting, sanding, or breaking asbestos-cement tiles poses a distinct health hazard.  These actions release asbestos fibers into the air, and breathing or ingesting these fibers is dangerous. If you insist on removing the siding, hiring a company that specializes in asbestos abatement is strongly recommended.