Finding old black mastic underneath flooring can immediately raise concerns, especially when the adhesive may contain asbestos.
A common question homeowners and contractors ask is:
Do I have to remove black asbestos mastic, or can I leave it in place and encapsulate it?
In many situations, asbestos-containing materials do not automatically need to be removed simply because they are present. The U.S. Environmental Protection Agency recognizes management in place and several forms of asbestos abatement, including encapsulation, enclosure, repair, and removal. The appropriate approach depends on the condition of the material and whether it will be disturbed during renovation or construction.
For intact, non-friable black mastic, properly encapsulating the adhesive may allow you to avoid the expense, mess, and potential disturbance associated with complete removal.
What Is Black Mastic?
Black mastic, sometimes called cutback adhesive or cutback glue, is an older type of flooring adhesive commonly found underneath materials such as:
- Vinyl composition tile
- Vinyl flooring
- Linoleum
- Carpet
- Wood flooring
- Other older floor coverings
It often appears as a black or very dark adhesive bonded to concrete or another substrate.
Some older black mastics contain asbestos, while others do not.
You cannot determine whether mastic contains asbestos simply by its color or appearance. If you suspect asbestos may be present, testing by an appropriately qualified professional or laboratory can help determine what you are dealing with before the material is disturbed.
Does Black Asbestos Mastic Have to Be Removed?
Not necessarily.
One of the most important things to understand about asbestos is that removal is not always the only acceptable way to address asbestos-containing material.
EPA guidance recognizes that asbestos-containing material may sometimes be safely managed in place. Where abatement is appropriate, possible approaches can include repair, encapsulation, enclosure, encasement, or removal.
Encapsulation involves covering or treating asbestos-containing material with an appropriate sealant to help prevent asbestos fibers from being released.
This can be particularly relevant with black mastic because attempting to remove an adhesive that is firmly bonded to concrete may require considerably more disturbance than simply leaving it intact and sealing it.
What Happens When Black Mastic Is Removed?
Removing black mastic can be much more complicated than removing ordinary flooring adhesive.
Depending on the adhesive and the removal method, contractors may attempt to use:
- Mechanical grinding
- Sanding
- Scraping
- Chemical solvents
- Adhesive removers
- Soy-based removal products
If the mastic contains asbestos, disturbing the material can create additional safety and regulatory concerns.
Asbestos removal may require trained or licensed professionals, containment procedures, specialized equipment, disposal procedures, and compliance with applicable federal, state, and local requirements.
State and local asbestos rules can also be stricter than federal requirements.
There can also be problems with the concrete after removal.
Even when most of the visible adhesive has been removed, the substrate may still contain:
- Mastic residue
- Oils
- Staining
- Solvent residue
- Removal chemical residue
These contaminants can interfere with the adhesion of new flooring materials.
That means removing the old mastic does not necessarily leave you with a perfectly clean surface ready for epoxy, thin-set, cement, or new flooring adhesive.
What Does It Mean to Encapsulate Black Asbestos Mastic?
Encapsulation takes a different approach.
Rather than attempting to physically remove the old mastic, the material remains in place and is covered with a coating designed to seal the surface.
The EPA defines asbestos encapsulation as treating the material with a sealant that binds the fibers together or coats the material so fibers are less likely to be released.
For flooring projects, encapsulation can help accomplish two goals:
1. Leave the existing mastic undisturbed
Instead of grinding or chemically dissolving the adhesive, the existing material remains in place.
2. Prepare the floor for the next flooring system
A compatible encapsulating primer can create a surface designed to accept another coating, adhesive, cement product, or flooring system.
This second step is particularly important.
Simply covering black mastic with flooring is not necessarily the same as properly encapsulating and preparing the surface.
Why Encapsulation Can Be Preferable to Removal
When intact black mastic is suitable for encapsulation, there can be several practical advantages.
Less Disturbance
Grinding, sanding, and aggressive scraping physically disturb the existing adhesive.
Encapsulation allows the mastic to remain where it is.
Less Mess
Mastic removal can produce debris or chemical sludge that must then be properly handled and disposed of.
Encapsulation avoids physically dissolving or stripping the entire adhesive layer.
Lower Project Costs
Professional asbestos removal can become expensive, particularly when containment, labor, testing, disposal, and other procedures are required.
Encapsulation may substantially reduce the scope of the project when it is an appropriate option.
Faster Floor Preparation
Removing decades-old adhesive from concrete can be extremely labor intensive.
Encapsulating the existing mastic can allow the renovation to move forward without first stripping the entire floor.
A Better Surface for New Flooring
Using a product specifically designed to encapsulate and prime mastic can also help create a surface suitable for new flooring systems.
Can You Just Install Flooring Directly Over Black Mastic?
This depends on the flooring system, but simply hiding exposed mastic beneath another floor is not always the best solution.
Old cutback adhesives can create bonding problems for materials such as:
- Epoxy
- Thin-set
- Tile
- Self-leveling cement
- Flooring adhesives
- Engineered wood
- Floor coatings
Standard primers and paints may not properly bond to asphaltic mastic.
The adhesive may also bleed through or interfere with the bond of a new coating.
For this reason, a specialized primer or encapsulant designed specifically for black mastic should be used when the new flooring system will bond to the existing surface.
How PerfectPrimer Encapsulates Black Mastic
PerfectPrimer® is designed to seal and prime black mastic, asbestos mastic, and cutback adhesive without requiring the existing mastic to be scraped, ground, dissolved, or removed.
PerfectPrimer can be applied directly over properly prepared mastic surfaces and is designed to create a compatible surface for new flooring materials.
According to PerfectPrimer’s current product instructions, it can be used beneath flooring systems including:
- Epoxy
- Cement products
- Thin-set
- Glue-down tile
- Engineered wood
- Flooring adhesives
- Other compatible finish systems
The product is specifically designed to seal cutback glues and asbestos mastics while avoiding grinding, scraping, solvents, soy gels, and complete mastic removal.
PerfectPrimer requires two coats for its listed applications, followed by the appropriate compatible finish or flooring system.
Should You Scrape Black Mastic Before Encapsulation?
If the mastic may contain asbestos, you should avoid unnecessarily disturbing it.
Do not automatically start sanding, grinding, or aggressively scraping a suspect floor.
The goal of encapsulation is generally to leave the existing material intact rather than mechanically removing it.
The floor should instead be prepared according to the instructions of the encapsulating product being used.
PerfectPrimer is specifically designed so that complete sanding or removal of black mastic is not required before application.
Can You Encapsulate Black Mastic That Does Not Contain Asbestos?
Yes.
Even when black mastic does not contain asbestos, removing it can still be unnecessary.
Old asphaltic adhesives can be difficult to remove and can interfere with the adhesion of many modern flooring systems.
Encapsulation can provide a practical way to isolate the old adhesive and create a suitable surface for the new flooring system without stripping the entire slab.
In other words, encapsulation is not useful only because of asbestos.
It can also solve the practical bonding problems associated with old cutback adhesives.
When Might Removal Be Necessary?
Encapsulation is not appropriate for every asbestos situation.
The condition of the material and the upcoming construction work matter.
For example, professional evaluation may be necessary when asbestos-containing material is:
- Significantly damaged
- Crumbling or friable
- Being demolished
- Being cut or penetrated during construction
- Located where future work will disturb it
- Subject to regulations that require a particular abatement procedure
EPA guidance specifically notes that the condition and location of asbestos-containing material, along with the planned use of the building, should be considered when determining how the material should be handled.
When in doubt about the condition of suspected asbestos-containing material, consult a qualified asbestos professional and follow applicable state and local regulations.
Removal Is Not Your Only Option
Discovering black asbestos mastic underneath your flooring does not automatically mean you need to grind it away or undertake a complete removal project.
For intact mastic that can safely remain in place, encapsulation may provide a much simpler solution.
Instead of disturbing the existing adhesive, a properly selected encapsulant can seal the old mastic and prepare the surface for the flooring system you actually want.
PerfectPrimer was developed specifically for this purpose.
If you have uncovered black mastic, asbestos mastic, cutback adhesive, or old flooring glue, learn more about PerfectPrimer and how you can seal the existing surface without grinding, sanding, or chemically stripping the mastic.
