Black Mastic Asbestos Basics and Removal

When removing old linoleum or vinyl flooring, you might be surprised to see smears of black adhesive between the tiles and the subfloor. Those smears and streaks just might be black mastic, a discontinued building product that often contains asbestos. Black mastic can be dangerous if you try to remove it. At the same time, it's considered to be benign and safe if left alone. Learn about black mastic asbestos, what it looks like, where it's found, and what to do if you find it.

What Black Mastic Asbestos Is

Mastic is a general term for a type of glue-like adhesive. Many modern mastics are latex, or water-based, and can be softened with water. By contrast, asphaltic cutback adhesive is an older type of mastic made with asphalt-based cement. The asphalt content lends mastic its black color. Asbestos was added to the mastic for its strengthening properties, not for fireproofing.

Concerns About Black Mastic Asbestos

Some, but not all, black mastics may contain 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.

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.

Where Black Mastic Asbestos Is Found

At one time, all resilient flooring was glued to the subfloor. While today you still can use adhesive-only flooring for a kitchen or bathroom—and it has its advantages—floating flooring and self-adhesive flooring are most common.

Common in homes built in the 20th century, black mastic was used as an adhesive for ceramic tile, linoleum, vinyl, and other resilient flooring materials.

What Black Mastic Asbestos Looks Like

You will only see black mastic asbestos 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.

In most cases, black mastic lies flat against the subfloor, with no ridges, bumps, or gaps of any significance. It often has faint embedded comb-like marks or 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.

How to Verify That It's Black Mastic Asbestos

Containing between 15- and 85-percent asbestos, black mastic adhesives were manufactured mostly in the first half of the 20th century. However, some companies produced asbestos adhesives as late as 1986. Therefore, if your house was built or remodeled around 1986 or before, there is a chance that black mastic adhesive on your floor may contain asbestos.

Testing the black mastic is the surest way to know if the mastic contains asbestos. DIY asbestos testing kits are available: the user scrapes off a test section, seals it in a plastic envelope, and sends the kit to a laboratory.

Short of testing the suspected material, another way to have a reasonable idea that the mastic contains asbestos is to locate an old can. In many old houses, you'll find old cans of paint and adhesives in attics, basements, under stairways, in outbuildings, or discarded in the yard.

Manufacturers of Black Mastic Asbestos

• Allied Signal, Inc.
• American Biltrite
• American Olean Tile Company
• Amtico Floors
• A.P. Green Industries
• Armstrong World Industries
• Asbestos Corporation, Ltd.
• Celotex Corporation
• Combustion Engineering
• Congoleum Corporation
• Crown Cork and Seal
• DAP, Inc.
• Durez Plastics
• Foster Wheeler Corporation
• GAF Corporation
• Garlock Packing Company
• Georgia-Pacific Corporation
• Hysol Aerospace Corporation
• Johns-Manville
• Kaiser Gypsum Company, Inc.
• Kelly-Moore Paints
• Minnesota Mining and Manufacturing (3M)
• Mobil Oil Corporation
• NARCO / Honeywell
• National Gypsum Company
• Owens Corning/Fibreboard Corporation

Brands of Black Mastic Asbestos

Prominent brands of asbestos-laced floor adhesive may include the following. In some cases, the products are still sold but without the asbestos content.

• 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

What to Do With Black Mastic Asbestos

Black mastic asbestos is safe if it is left alone, undisturbed, and encapsulated, such as by covering it with new flooring.

The material 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 no practical way to get rid of it safely.