Asbestos-containing materials (ACMs) are any materials containing a discernible amount of asbestos, that is, amounts over 1% by weight. (Air-borne asbestos is considered as any amount over 0.01 fibers per cubic centimeter).
Asbestos is added to building materials as a fire retardant, and also as a binder, to introduce some measure of dimensional stability. This has been done routinely as part of fabrication of numerous materials during a period of over ninety years, from 1910 to the present. Use of ACMs in building began to be lessened in 1976, and a major seven-year phase-out began at the end of the 1980's. Today there is no asbestos in modern residential construction, although there is still some use of it in industrial materials.
Asbestos is found in these materials in varying amounts. Depending upon the composition of such building materials, the asbestos contained in them is more prone or less prone to being released into the surrounding environment (friability). Asbestos is described as friable or non-friable depending upon how tightly it is bound into the ACM matrix. Wear-and-tear, refinishing, renovating and demolition can free up and release asbestos fibers from the ACM matrix, at which point they can become a hazard.
Some building materials are almost completely made of asbestos; of these asbestos pipe wrap is very friable once the outer cloth-and-plaster covering has been breached, and so is potentially very hazardous. Two other materials that have a high amount of asbestos are transite flue pipe and asbestos sheet, which are composed of asbestos and cured cement; they are not very friable.
Asbestos is encapsulated, isolated or removed - the method dictated by regulations - when it is abated. In an owner-occupied single-family dwelling only, two good coats of normal latex paint are considered an excellent method for the home-owner to encapsulate worn asbestos pipe wrap, as long as it is not too worn.