There was once a time when the practice of gluing flooring to a subfloor was common. It is less typical of an approach today due to the unattached, or floating, style of floors now available.
Though adhesive-only flooring can still be used and has some draws to it, some disadvantages keep it from seeing a popular resurgence.
For homeowners renovating their floors, it may be a surprise to lift the flooring and see black adhesive beneath the tiles or linoleum. This is known as black mastic; more often than not, it contains asbestos.
Wondering what it is, what it looks like, if is it dangerous, and much more. Let’s address all these questions…
What is Black Mastic Asbestos?
Black mastic was a material commonly used as an adhesive for linoleum, ceramic tile, and other such materials for floors in the 20th century.
It’s a general term for glue-like adhesive for flooring, and many modern mastics tend to be water-based or latex based, so they can be softened using water.
However, the old kind of mastic is made using asphalt-based cement. And the biggest issue with this old black mastic is that it commonly contains asbestos, though some do not.
Asbestos has been shown to cause life-threatening health problems in the form of mesothelioma. If you plan to do anything with the old black mastic, you should ensure you are not using the dangerous kind.
Many kinds of cutback adhesives have asbestos in them, and it is believed that this material was added to make the compound resistant to fire. Though this would give a slightly effective resistance, asbestos simply made the product long-lasting and more durable. This is due to the higher fiber count of asbestos, which locks up to make the mastic stronger.
The Appearance of Black Asbestos Mastic
The only time you will most likely see black mastic asbestos is once a floor covering has been lifted off.
Black is the main color, as its name indicates, but there may be other colors you may notice in the mastic, too. Like colors from the floor covering that aren’t totally removed or any traces of the subflooring peeking through.
Keep in mind that some water-based latex adhesives were also black and dark gray, so you should not use color only to identify black mastic.
In many cases, you will see that true black mastic sits flush against the subfloor and has no gaps, bumps, or ridges of any significant size. It will usually feature comb-like marks embedded into it from when it was initially applied.
Potential asbestos in the black mastic will not be able to be seen with the naked eye. Though cutback adhesive isn’t affected by most cleaners and water, if you sand it vigorously, it would become tar-like and thick from the heat produced. However, this is not recommended because of the potential asbestos risk.
Can You Seal or Paint Over Black Mastic?
While not a very safe option, property owners have numerous methods to seal black mastic and then cover it with paint, epoxy, or their preferred flooring material.
The top three non-toxic options are Ardex cement overlay material, Fiberlock coating-like sealer, and a combination of sealer/primer products. Most of the time these aren’t recommended to be dealt with without professional help.
The experts are familiar with the task of painting atop black mastic, testing for asbestos in both black mastic and cut-back adhesives, and so much more among other significant tasks which sometimes also include removing the black mastic entirely with a combination of scraping and using a heating gun.
Is it Safe to Have Black Mastic Asbestos Flooring?
It is safe to have this mastic around if you leave it undisturbed, covered up, and don’t ever touch it. You can do this by covering it up with new flooring.
If the material is disturbed and the fibers are introduced into the air, it becomes dangerous. It is most toxic when these fibers are floating through the air since they can be breathed in or spread around by humans.
The only way that asbestos is completely safe is when you do not expose it to any activity that could bother it, like walking on it or sanding it down.
When you run into black mastic asbestos, it is better if the old flooring remains where it is and is just covered with new flooring.
Many kinds of floors can be installed over old floors as long as the old floor is well-adhered and flat. Unless you are removing the new floor in the future, you shouldn’t have to be too concerned with covering up old black mastic.
Safe Ways to Determine if You Have Black Mastic Asbestos
As mentioned, black mastic glues were made primarily in the first part of the 20th century. This type of mastic contained between 15 and 85 percent asbestos.
Even so, some companies were making asbestos-based adhesives as late as 1986, when the practice finally stopped.
If your home was remodeled or built before 1986, you might be at risk of having black mastic adhesive on the floor that has asbestos in it.
Besides testing the material, one of the easiest ways to figure out if there is mastic in your home is to try to locate an old can of it that holds the leftover product that could still exist.
It may be stored in the basement, attic, under a stairway, or in a shed outside. Some of the known manufacturers of black mastic asbestos to look out for are:
- American Biltrite
- Amtico Floors
- Armstrong World Industries
- Asbestos Corporation, Ltd.
- Celotex Corporation
- Congoleum Corporation
- Garlock Packing Company
- Mobile Oil Corporation
- National Gypsum Company
- 3M (Minnesota Mining and Manufacturing Company)
The Bottom Line
Black mastic asbestos is a type of adhesive common in homes built before 1986.
While asbestos has been shown to cause mesothelioma, finding black mastic in your home doesn’t automatically mean you are being exposed to the dangerous material.
If you determine there is black mastic asbestos in your subflooring, you can live with it safely by not disturbing it or not removing more of the flooring. Instead, install new flooring over top of it, and you can be sure it is properly covered and safe.
Jack Luis is a semi-retired painter who loved painting his clients’ ideas on their walls.
He had worked as a painter for over a decade serving customers in areas such as Charleston, Mount Pleasant, Beaufort, and Georgetown, SC (South Carolina). Today in his free time, he likes to read and write about the newer techniques implemented in his profession. You may read more about him here or get in touch with him here.