Asbestos Cement Siding

Asbestos cement is a composite material consisting of Portland cement reinforced with asbestos fibers.  Asbestos cement first came into use as an exterior cladding after 1907. By the 1920s, the National Board of Fire Underwriters recommended that asbestos cement replace wood as siding and roofing material because of its superior fire-resistant properties.  By the 1940s, hundreds of thousands of homes in the U.S. had been constructed using asbestos cement siding.

During the late 1960s and early ‘70s, however, the news media began to report on the health hazards associated with asbestos.  As reports increased, concern grew, so the federal government took action.  The EPA banned the use of asbestos in the manufacture of building products in 1973.

In the course of my Home Inspections In the Colorado Springs area I inspect many older homes that have Asbestos Cement siding.  I always inform the buyers of the advantages and disadvantages of this product, but as it was intended it provides a good fire barrier. Asbestos  siding photo

When trying to determine if you have Asbestos Cement siding, beware that other wood siding can look like Asbestos Cement siding, a simple pick test will let you know.  Use a sharp tool to test your siding, if you have wood siding you can gouge a small portion off, but if you have Asbestos Cement siding it will be similar to gouging your cement sidewalk.
Health Risks

Asbestos fibers are a proven health hazard if inhaled.  Asbestos dust is a known cause of a type of lung cancer called asbestosis.  Mesothelioma, another deadly form of cancer that attacks internal organs, can also be caused by exposure to asbestos.  However, asbestos cement siding that has been properly installed and is not in a state of decay presents no health risks as long as it remains undisturbed.  This is because the cement binds the asbestos fibers and prevents their release into the air, under normal use and maintenance.

The EPA deems asbestos to be hazardous when it is in a friable state, meaning that it can be crumbled, crushed or pulverized by hand pressure.  Crushed asbestos in a powdery form can allow its particles to become airborne and inhaled, causing potential health problems.  Asbestos cement products that are not in a friable state are not considered hazardous.  The only potential danger is when the cement is disturbed in a way that causes the asbestos fibers to become airborne.

If mechanical activities performed on the siding, such as chipping, sawing, grinding or sanding, allow particles to become airborne, then the cement is considered in a friable state and, consequently, hazardous.  Deterioration can also lead to particles becoming airborne and potentially dangerous.Asbestos Siding photo from home inspection


•    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.

•    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.
•    This product cannot be refurbished, however replacement siding is available.

Damage and deterioration can lead to structural and health issues, so proper maintenance of asbestos cement building materials is a primary concern.  Keeping the siding clean and performing minor repairs as soon as they become necessary are very important.  Asbestos cement siding is fairly brittle and has little resistance to cracking, chipping and damage from impact, which can cause asbestos particles to become airborne.  Damage to the siding can also lead to other damage related to moisture intrusion which can then lead to mold growth. Damaged areas that cannot be fixed but can be replaced with non-asbestos fiber cement by a professional.  Specific fiber cement materials have been manufactured for repairs that are intended to mimic the look of asbestos cement siding.