Microscopy in the Study of Asbestos-Containing Joint Compound and Patching Products, Including Spackling

Abstract

Drywall (wallboard, plasterboard, gypsum board) became the common construction material for interior walls in buildings in the later 1940s. Joint compound (mud, spackling, taping compound, joint treatment material) and patching products such as spackle or spackling were used to seal the seams between the boards and cover cracks and nail indentations. Most joint compounds from the 1940s into the later 1970s contained chrysotile asbestos in various formulations. Analyses by microscopy determined the chrysotile asbestos content of samples of Bondex, Georgia-Pacific, and Reardon products to be 1–5%, 3–8%, and 1–2% asbestos, respectively. Information compiled from several sources, including corporate responses to the U.S. EPA Asbestos Information Act of 1988 and other documents, suggest that asbestos-containing joint compounds and patching products from the 1930s into the late 1970s contained chrysotile in the range of 0.5% to 23%, with one company having a few formulations with asbestos levels as high as 45.2%. Although there were no documents showing that amphibole asbestos was intentionally added to joint compounds, there is some evidence of amphibole asbestos fibers in certain joint compound products, probably as accessory minerals with added chrysotile, talc, or limestone. No amphibole asbestos fibers were found in a Georgia-Pacific joint compound product tested using the acid/base digestion preparation procedure. During simulation testing, the asbestos level in the breathing zone of a worker during the mixing of Bondex Joint Compound ranged from 6.9 to 12 asbestos fibers per cubic centimeter of air (F/cc) (phase contrast microscopy modified by transmission light microscopy). The level was below detection during application. During sanding, the asbestos level in the breathing zone of the worker ranged from 1.9 to 5.5 asbestos F/cc. The simulations showed results that were within the ranges reported in the scientific literature for airborne asbestos levels caused by dry mixing and sanding of asbestos-containing joint compound. The sale of joint compound and spackling sold for consumer use with intentionally added asbestos was banned by the Consumer Product Safety Commission in 1977.