A phenomenon that modern homeowners don’t often come across may be more familiar to those who buy older houses.
The discovery of a black mastic underneath old vinyl floor tiles. Not only does this black mastic smell, but it can also be potentially harmful.
The smell of black mastic or cutback adhesive comes from the bituminous resin and naphtha solvent used in its makeup. The smell itself is not dangerous, although it is unpleasant.
Although, black mastic may contain asbestos fibers, so you should treat it with caution.
What’s In Black Mastic To Make It Smell?
Mastic is a term used in the early 20th century to describe an adhesive that contained asphalt.
These adhesives were used to stick vinyl asbestos tiles or vinyl composite tiles to the subfloor. Apparently, with the intention that they would never be removed again!
However, they often contained asbestos fibers which were added to make the glue more resilient and durable. This is why you should be very cautious if you encounter this black mastic in your home.
The ingredients in black mastic or ‘cutback’ as it was known, were asphalt bituminous resin, solvent, and fibers.
The asphalt bituminous resin was the substance that stuck the tiles to the subfloor. Asphalt is a viscous form of petroleum and has a very strong odor.
The solvent, usually naphtha, was used to thin the resin to make it more spreadable. Naphtha is another byproduct of petroleum, so it is not surprising that it has a strong, and enduring smell.
Fibers were used in the mastic to strengthen it. Asbestos fibers were used until 1986 when they were banned and replaced with olefin fibers.
The smell that people associate with black mastic comes from the combination of asphalt bituminous resin and solvent.
Getting Rid Of Black Mastic Smell
Once you know what you are dealing with you have a few options for getting rid of the black mastic smell.
We chose to remove it altogether to avoid running into any more issues in the future, but you could also choose to seal or cover it.
You can use chemicals to remove the mastic but be aware this can cause issues with laying new flooring afterward.
The concrete can absorb the solvents and any residue may cause problems by reacting to the adhesive of new floor coverings.
Still, by removing the black mastic you should also get rid of the smell.
Sealing or encapsulating the black mastic will also help to get rid of the smell. You will need to remove as much of the cutback as possible first. For ease, use a power scraping device for this job.
Then you can apply the encapsulating substance to the floor surface. This is usually a polymer layer of material.
Finally, to get rid of the black mastic smell you can cover the floor. You’ll still need to remove as much of the cutback as possible first. Then you can add a cementitious barrier or underlayment compound on top of the mastic.
You’ll then be able to put on a new floor covering over the top of this material.
How To Recognize Black Mastic?
You’ll usually only ever see black mastic in older homes when you are pulling up old floor coverings. Typically the smell will give away its identity.
Some older water based adhesives were also black, so the color alone isn’t enough to identify cutback adhesive.
Consider the date of the house and when it was built. A property from pre-1986 is more likely to have black mastic than one built after that time.
Is Black Mastic Safe?
Remodeling an older property frequently means ripping up old flooring.
If you come across a sticky black substance underneath old tiles or other floor covering then it’s best to stop work. It could contain asbestos and if so, will need a professional to deal with it.
They will send a small sample sent to a lab, taking any guesswork out of the issue. This will let safely carry on removing the black mastic. The smell of the black mastic is not a health issue.
Removing Black Mastic
It is always better to employ a professional for any job that may include asbestos. Over time mastic gets brittle and if you remove it there will be particles escaping into the air.
One removal method is called wet scraping which ensures that the black mastic remains wet for the entire removal process. This reduces the chances of fibers getting into the air and the risk of you inhaling them.
While it is possible for you to do this it’s best done by a professional with the right equipment and PPE.
Even if you could guarantee keeping the mastic wet for removal you will still end up with material that may be asbestos contaminated. You will then need to dispose of this material.
If in doubt, get help. The consequences are not worth thinking about.
Things To Consider
Not all black mastic will contain asbestos. Post 1986 cutback adhesive no longer contained asbestos fibers. However, you won’t be able to tell which is which just by looking at it.
Neither will the smell tell you. Asbestos has no detectable odor. What you are smelling is the resin and solvent present in both the asbestos fiber and olefin fiber black mastic.
Black mastic that contains asbestos fibers is best left undisturbed. The danger from asbestos is when its fibers get into the air and are breathed into the lungs. Undisturbed asbestos is the safest type.
If you know there is cutback adhesive underneath old vinyl flooring then it is best to leave the flooring in place. Simply cover it over with a new floor.
This removes the need to disturb the black mastic and the resulting smell, mess and health concerns.
Coming across black mastic in your home can be a worry. The smell can be awful and then there are the concerns about asbestos fibers.
If you are in any doubt about the type of black mastic it is worth consulting an asbestos professional to put your mind at ease.