Prior to the advent of environmental protection laws restricting the use of asbestos in common building materials, builders sometimes incorporated asbestos in plaster to achieve a number of desirable effects. Some of these benefits include fire resistance, increased material strength, and improved sound absorption. The most common use of asbestos in plaster in the United States was in “popcorn” ceilings from the late 1950s to the 1980s.
Popcorn (or “acoustic”) ceilings were very popular prior to the 1990s for a number of reasons. The treatment could be applied quickly, easily, and cheaply with a simple spray gun. The pebbly surface that results is ideal for absorbing sound, improving the acoustic quality of buildings. The texture also effectively conceals stains and defects in the underlying surfaces. This flaw-masking quality of the treatment allowed builders to produce attractive finishes much more quickly than they could produce a high-quality painted surface. Especially prior to the common use of cheap, modern latex paints, the cost of painting made the use of popcorn ceilings a much cheaper alternative.
Unfortunately, some older buildings still have popcorn finishes remaining, and the nature of removing them make them a particularly dangerous building material in terms of asbestos abatement. The presence of asbestos in plaster ceilings requires professional removal to deal with the significant health risks and strict regulations enacted by the Environmental Protection Agency.
Plaster with asbestos mixed in as a strengthening fiber is not normally found as the primary construction material for walls, although exceptions certainly do exist. Traditional lath and plaster walls generally use horsehair as the strengthening fibers. The popularity of asbestos did not peak until after traditional plastering methods had largely been replaced with faster, easier drywall techniques. Drywall overtook lath and plaster as a primary wall material during World War II, when there were not enough skilled plasterers to keep up with demand. Unlike plaster walls, it is very common to find asbestos in drywall wallboard.
One major exception to the use of horsehair in plaster may be curved wall surfaces built from the late 1940s to the 1980s. Because drywall is rigid and brittle, it cannot be curved around a tight radius. Curved walls and archways are sometimes still created with traditional lath construction techniques to overcome this problem. During the aforementioned time period, plaster with asbestos strengthening fibers would likely have been used for these curved wall sections. A lack of dark horsehair strengthening fibers in hard plasters is a strong warning sign that there may be contaminated, and any light-colored fibers visible in hard plaster are very likely to be asbestos.
Plaster used as a dedicated fireproofing layer any time prior to the mid-1980s almost certainly contains a large percentage of asbestos fibers. While plaster is itself fireproof, the addition of asbestos made it possible to achieve higher levels of heat and flame resistance with a much thinner application. The fireproofing was also much stronger and damage resistant, making the presence of asbestos fibers practically a given in such applications.
When in doubt about the presence of asbestos in plaster, the following advice from the EPA should be your golden rule:
If in doubt, treat the material as if it contains asbestos or have it sampled and analyzed by a qualified professional.
Don’t disturb, damage, or attempt to remove questionable materials in any way, as doing so can actually create more of a hazard than simply leaving the material in place. Seek professional help in analyzing the material, and always hire an asbestos abatement specialist if contaminated materials need to be removed.