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Cement asbestos siding is a composition of Portland cement, sand and asbestos. The
asbestos is a mineral that comprises about 5% to 10% of this siding product, and
is used as a binder because the cement is so fragile at this thickness. This
siding is fireproof and relatively brittle. Cracking and breakage is fairly
common. In many states, asbestos is considered a hazardous material when it can
become airborne or friable. Friable asbestos fibers are easy to inhale. The
human body has the ability to discharge larger asbestos particles, however, the
particles that are only visible with a 400-power, photo sensitive microscope are
not likely to be discharged from the body, but become lodged in the lungs.
Depending on the person and the amount of exposure, health problems may develop—Asbestosis
or Mesathelioma being the worst problems.
Since residential building products have not been
manufactured since 1973 and not installed since 1978, most of the
asbestos-containing cement siding is older and may typically exhibit some
cracking and breakage.
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Check for cracked, broken
pieces, especially along the bottom of the wall.
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Check to make sure that the
nails are not coming loose. When the siding was most popular, the
sheathing of choice was 1/2 inch building board, such as Celotex. This
material was okay for aluminum siding and wood sidings, because the
sidings were nailed to the wall studs. Cement-asbestos siding was never
on a 16 inch nailing pattern, so 3/8 inch thick nailing strips were
nailed horizontally across the wall studs to receive the siding nails.
If plywood sheathing were used, you could nail this siding anyplace.
Look for the nailing strips at the bottom of each course. They should
look like a reveal or shadow line. If they are not present, check to see
if the siding was nailed to plywood. If neither is present, the siding
is either loose or the paint is holding it on.
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Check for felt paper backer
strips behind every vertical butt joint to deflect rain that gets behind
these joints. A good place to look for problems is at the sill plates on
the inside of the basement or crawl space. If they are wet or stained,
this may be the cause, especially on the west side of the house, since
that is where the prevailing weather comes from.
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Check that the bottom of the
siding is well above the grade.
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Research your local
regulations to determine whether or not handling cement asbestos siding
is considered a hazardous waste in your area.
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