What You Should Know About Asbestos-Cement Siding

Asbestos-Cement Siding

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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 documented, and any homeowner is advised to exercise caution when it comes to a building material that contains asbestos.

But in reality, removal of siding containing asbestos often is more hazardous than leaving it in place. If left alone, asbestos-cement siding and other building products containing asbestos can be considered to be benign.

Warning

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. 

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.

Picture of Asbestos-Cement Siding

Asbestos-cement siding comes in many forms, but it often has low vertical grooves. It is punctured around the perimeter in various spots with nails and each row is lapped over its lower, adjacent row.

Broken asbestos-cement siding tiles are rough, flaky, and sharp along the broken edge.

When you gently rap a suspected asbestos-cement siding tile, it will produce a sharp sound like when tapping on a ceramic tile (be careful not to break it).

Asbestos-Cement Siding

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What Asbestos-Cement Siding Is

Asbestos-cement siding is siding made from a mixture of Portland cement reinforced with asbestos fibers. The Portland cement binds asbestos fibers into a hard mass.

While asbestos is fireproof and can help limit or stop the spread of fire, the asbestos was actually added to the cement as a binding agent to lend strength to the material.

History of Asbestos-Cement Siding

Asbestos cement was first developed in 1905 by the Johns-Manville company, which 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 encapsulated and neutralized the asbestos fibers.

This theory was later proven 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.

Asbestos-cement was not only commonly used but it was a recommended siding material from the 1940s to the 1960s, due to its extremely durable and fireproof nature.

Pros and Cons of 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. When the siding is undisturbed and in good shape, the health hazards are minimal. The presence of asbestos-cement siding, in and of itself, is not a serious drawback.

Pros
  • Asbestos cement siding is highly fire-resistant and will not burn or melt the way vinyl and wood siding will.


  • Resists insect damage and rotting.

  • Manufactured with textures intended to simulate the look of other cladding materials, such as wood grain.

  • 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.


Cons
  • 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.


  • Difficult to find replacement asbestos-cement siding for repairs.

  • Should not be refurbished or altered, other than painting it.

Why Removal of Asbestos-Cement 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 safer 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 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 an 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 usually acceptable to home inspectors and real estate assessors, and it rarely has any negative effect on home values. 

Asbestos-Cement Siding Basics

  • Homes built between 1920 and the 1960s 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 a significant real estate value benefit. 
  • Cutting, sanding, or breaking asbestos-cement tiles all pose a distinct health hazard. 

Warning

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.