Common in homes built in the 20th century, black mastic was used as an adhesive for ceramic tile, linoleum, and other flooring materials. When you remove that floor covering to make way for new flooring, you may encounter the mastic and wonder whether it is safe to remove. The main concern surrounding this question is that black mastic often contains asbestos. Asbestos has been proven to cause a life-threatening condition called mesothelioma. So before you do anything with black mastic in your home, it is important to identify it and deal with it appropriately.
What Is Black Mastic?
Mastic is the general term for a type of glue-like flooring adhesive. Many modern mastics are latex, or water-based, and can be softened with water. Asphaltic cutback adhesive is an older type of mastic made with asphalt-based cement. As a petroleum-based material, the cutback is not softened by water. Some cutback adhesives contained asbestos. It is commonly thought that asbestos was added to these compounds for fire-resistance. While this would have a residual effect, the primary purpose of the asbestos was to make the product more durable. Asbestos is a highly fibrous material, and these fibers interlock to help strengthen mastic, insulation, and many other household building products.
What Does Black Mastic Look Like?
You will only see black asbestos mastic after a floor covering has been removed. As the name suggests, black is its predominant color. But there may be traces of other colors, such as those from subflooring showing through the mastic or pieces of floor covering that were not completely removed. Note that some older latex (water-based) adhesives also were black, so color alone is not a reliable identification characteristic.
In most cases, black mastic lies flat against the subfloor, with no ridges, bumps, or gaps of any significance. It often has faint embedded swirls from its initial application. No asbestos fibers in the mastic will be visible to the bare eye. While cutback mastic is not affected by water and many cleaners, if it is vigorously sanded (not recommended, due to the asbestos risk), it would become thick and tar-like from the heat.
Does My Floor Have Asbestos-Based Floor Adhesive?
Containing between 15 and 85 percent asbestos, these adhesives were manufactured mostly in the first half of the 20th century. However, some companies produced asbestos adhesives as late as 1984. Therefore, if your house was built or remodeled around 1984 or before, there is a chance that black mastic adhesive on your floor may contain asbestos.
Makers of Black Mastic
The Peterson Firm LLP, a Washington DC law firm that deals with mesothelioma cases, notes that the following companies manufactured adhesives containing asbestos:
- 3M (Minnesota Mining and Manufacturing Company)
- American Biltrite
- Amtico Floors
- A.P. Green Industries
- Armstrong World Industries
- Asbestos Corporation, Ltd.
- Celotex Corporation
- Crown Cork and Seal
- Congoleum Corporation
- GAF Corporation
- Garlock Packing Company
- Johns Manville
- Mobile Oil Corporation
- National Gypsum Company
Prominent brands of asbestos-laced floor adhesive include:
- Armstrong S-89 Adhesive
- Armstrong S-90 Adhesive
- Atlas Stove & Furnace Cement
- Carey Fibrous Adhesive
- Empire Ace Fibrous Adhesives
- J-M Fibrous Adhesive Cement
- Crown Coat Cement
- Gold Bond Laminating Adhesive
Is Black Asbestos Mastic Safe?
Yes and no. It is safe if it is left alone and encapsulated, such as by covering it with new flooring. It is unsafe if it is abraded so that its fibers are released into the air. Asbestos is most dangerous in its friable state, in which tiny, light fibers float through the air and can easily be spread or ingested or aspirated by humans.
The only state in which asbestos is truly safe is when it is not exposed to an activity that may abrade it, such as sanding it or even walking on it over time. It is best if the old flooring covering stays in place and is covered with new flooring. Many types of flooring can be installed over old flooring, provided the old flooring is flat and well-adhered. Unless a new floor is removed in the future, there should be no safety concerns about covering old black mastic.
The worst thing to do is to attempt to grind it off with a drum sander or to scrape it off manually. Because cutback mastic is thick, gummy, and difficult to remove, there is a practical way to get rid of it safely.