Cement Asbestos Siding

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.

• Check for cracked, broken pieces, especially along the bottom of the wall.

• 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.

• 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.

• Check that the bottom of the siding is well above the grade.

• Research your local regulations to determine whether or not handling cement asbestos siding is considered a hazardous waste in your area.