Types of Wood
Flooring Adhesives
FAST FACTS > > >
Adhesives work by creating a bond between the substrate and the
flooring through a chemical reaction.
While all adhesives work on the same principle of changing from
a liquid to a solid state, they differ by the carrying agent or
catalyst that activates them. The most common types of wood
flooring adhesives include: |
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Water based adhesives
certified as "very low emission" are the first choice for
health and environmental protection. They are
free of solvents or VOCs and safe to install. However, their
range of application concerning certain types of wood floor or
sub floor is limited.
Solvent based adhesives are
well proven for wood floor installation over
several decades offer a large range of application but contain
non-hazardous solvents which will evaporate during the first
weeks after installation is completed.
Urethane based/
moisture-cure adhesives
offer the largest range of application and
highest installation security but are usually more expensive
than other adhesives. The can be applied under almost any
circumstances and have hardly any restrictions on type of wood
floor or sub floor.
Powder adhesives work pretty
much the same way as water based adhesives, except you add the
water yourself and thus do not have to worry about freezing or
transportation of extra weight. The cement that
is in the powder will permanently bond most of
the water resulting in a reduced wood
swelling compared to water based adhesives.
Technical Overview
~ A general rule of thumb for any adhesive is not to spread more
than you can cover in 15 to 20 minutes.
~ Many failed glue-down floors are caused by contractors not
taking the time to properly check and prepare
the subfloor.
~ The adhesive’s spread rate is controlled by the shape and size
of the trowel’s notches.
~ If you are familiar with one product and switch to another,
don’t assume you can use the same trowel or
spread rate.
~Using adhesives in the correct wood flooring application is a
key to success. Certain wood flooring products
and substrates work best with a glue-down method of
installation. Adhesives are most commonly
used with engineered wood flooring installed over concrete, as
well as parquet installed over a slab or plywood.
~Many adhesives have a recommended “flash time”— they must be down for
a certain amount of time before the wood flooring is installed.
Other adhesives are “wet-lay,” which don’t need flash time, and
you can lay the wood flooring into them immediately. The
technology and chemicals in each manufacturer’s adhesive vary,
so always refer to the manufacturer’s guidelines for how much,
if any, flash time is required. A general rule of thumb for any
adhesive is not to spread more than you can cover in 15 to 20
minutes. This is your window of opportunity to bond the flooring
to the adhesive. If the adhesive is exposed longer, it may start
to dry out and not transfer to the flooring surface. Other
factors such as relative humidity may also affect open times for
some adhesives, so it’s a good idea to check job-site conditions
and document all of your findings before you install. To ensure
a proper bond between the adhesive and floor, some manufacturers
recommend rolling the wood floor in all four directions with a
100-pound roller.
Many failed glue-down floors are caused by contractors not taking the
time to properly check and prepare the subfloor. A concrete slab
should be clean, dry and flat. If a slab isn’t clean, the
adhesive will form a bond with the debris, not the slab.
Contaminants such as paint overspray, plaster or adhesive
from an old floor covering may interfere with adhesion, so the
slab may have to be abraded with a heavy-grit sandpaper and
hard-disc plate. Thoroughly vacuum, and if necessary, wetmop the
slab to remove all dirt and debris.
In new construction, the slab should have cured at least 60 to
90 days before testing and installation. Take several readings
with a concrete moisture meter, or perform a calciumchloride
test or a phenolphthalein test according to instructions. If
necessary, use the recommended moisture barrier, such as 6-mil
poly. A high pHlevel can also adversely affect the performance
of an adhesive, so some manufacturers also
recommend performing an alkalinity test. Installing a floor over
an uneven slab can cause the adhesive
to adhere to some spots in the flooring and not others. This
creates a common customer callback of hollow spots in the floor
that make a popping sound when walked on. For glue-down
installations, a flat slab has a tolerance of 3⁄16 of an inch
over a 10-foot span or 1⁄8 of an inch over a 6-foot span. To
even out a slab, high spots can be ground down, or low spots can
be filled with an approved leveling compound. The subfloor
should be compatible with the adhesive and product you’re
installing. Super-slick concrete slabs can interfere with the
adhesive’s bonding ability, so the surface of the slab may need
to be abraded. Other surfaces, such as lightweight concrete, may
not be compatible with certain adhesives, so always double-check
with the manufacturer before you install. For a glue-down
installation, the plywood subfloor
should be at least 5⁄8 inch thick in 4-by-8-foot sheets. Always
check with the adhesive and flooring manufacturers for subfloor
requirements. (Acknowledgment:
Parts of the above information is from
Hardwood Floors,
the official magazine of the
National Wood
Flooring Association 09/06 issue)
Wood Floor Adhesive
History & General Information
Modern
technology has developed wood flooring qualities and finishes
that have never before been available. Never have there been
more colors, patterns, styles, and types of wood floors. The
technology that has emerged from the chemical and adhesives
companies has contributed greatly to the use of wood flooring
and expansion in commercial and residential construction. New
adhesives today enable us to use wood floors products in
applications that just a few short years ago would have been
prohibitive. These new adhesives in turn have contributed
greatly to the increased use of wood flooring in all types of
new construction as well as in remodeling.
It has not always
been this way. Limitations were placed on the use of wood
flooring in many areas because of the lack of good installation
systems. It has only been in the last 50 years that adhesive
installed floors have become common. It is interesting to look
back over these 50 years and see just how adhesives have played
a role in the growth of the wood flooring industry and how the
evolution of different adhesives occurred, each solving some
problems of its predecessor but creating new problems of their
own.
Let's examine this
evolution by adhesive types. And examine the pros and cons of
each adhesive type or system. We'll then take a crystal ball
look into the future to see what may lie ahead of us in a world
of modern technology that constantly faces government and
political controls.
The very first
installer of wood flooring with adhesives was probably an
ex-roofer. He had an old smelly asphalt wagon that he
practically set on fire to soften the asphalt into a workable
consistency. While the application was not very pleasant, his
mentality was exceptionally keen to have the foresight to
experiment with these asphalts for installing wood flooring. The
system was simple in a way but very difficult and definitely not
the type installation that even the experienced flooring
installer could easily master. Nevertheless it worked, by hot
mopping asphalts on a substrate and then embedding wood flooring
into the asphalt. Thus, adhesive installed wood flooring systems
were born.
One can only be
somewhat awe struck by the problems with this type of
application. Without a doubt it was messy; results were
inconsistent; it was smelly; it was somewhat hazardous; clean up
of smears and slop overs was nearly impossible; mistakes and
repairs were difficult to handle. About the only good thing was
that for the first time someone had the idea for a new method of
installing floors that would ultimately contribute greatly to
the tremendous growth that the industry has experienced.
Without a doubt the
old smelly asphalt furnace on a trailer had to go and be
replaced by some type of system that was controllable and easier
to apply. Since asphalts were already being used, then why not
continue to use asphalts but devise a better application method.
This thinking led to the development and use of "asphalt
cut-backs". They were called "cut-backs" because the old solid
blocks of asphalt were "cut-back" with a flammable solvent such
as mineral spirits, to make them fluid. They were then filled
with materials, sometimes asbestos, to provide a uniform
viscosity or thickness. Now an adhesive was available that could
be purchased in a container, actually troweled on a substrate,
and then you install wood flooring in the asphalt mastic. The
release of the solvent caused the asphalt to 64 set up" and
provide a bond. This type material is still used today. It
overcame many of the problems of the old hot-mopped asphalt but
then it created some very important new problems.
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The most serious
problem was that of flammability. It was not uncommon to
trowel out very large areas before installing any flooring
because the working times were extremely long. This
saturated the surrounding areas with solvent vapors and
carelessness on the part of the mechanics caused serious
fires and explosions.
-
The flammability
resulted in greatly increased insurance premiums.
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The technology
involved in the formulation was not very sophisticated and
some very questionable compounders began formulating these
materials.
-
Asbestos, a
common filler that was low in cost, was used but later found
to be an extremely hazardous material for the compounders to
handle and ultimately was banned. The result was formulation
with different fillers that increased prices of an already
questionable material.
Clearly, the days of
asphalt cut-backs were numbered and something had to be done to
replace these materials for the installation of wood flooring.
Mastic application of wood parquet floors was firmly in place in
the industry. The market had become sizable and new flooring
products were being developed by the manufacturers that required
a quality mastic without the inherent problems of the asphalt
cut-backs. Thus the modern day chlorinated solvent mastics and
some emulsions for special applications of finger block were
developed.
To many, this sudden
evolution from asphalt cut-backs into chlorinated solvent and
emulsion formulations came as a shock. All of a sudden the price
per gallon of adhesive sky rocketed and the days of $1.00 per
gallon asphalts were gone forever. From an industry point of
view however, this was not all bad because for the first time a
technology was spawned that was instrumental in the rapid growth
of the wood flooring industry. The technology created some very
important situations and advantages.
-
For the first
time the burden of performance was placed on the
manufacturers of the adhesives. Heretofore, this
responsibility rested almost entirely with the installer and
he was at the mercy of the quality level of the cut-backs.
The installer was also liable for the hazardous
characteristics of the adhesive.
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The ease of
application and use of these new mastics opened up new
horizons for installers that previously would not have
attempted to install wood floors in mastics.
-
For the wood
flooring manufacturers, it presented new opportunities for
research and development of different patterns and flooring
types, thereby expanding the market.
-
Eliminated were
the hazards associated with flammable products which
resulted in reduced insurance rates and liability.
-
The technology
involved in the formulation and manufacture of these new
mastics is provided by manufacturers who are far more
sophisticated in their research, development, and production
than the manufacturers of the past. No longer is it possible
to set up a "garage operation with a cement mixer" to
produce these formulations. You are for the most part
supported by reputable and quality oriented manufacturers.
Just what is it
about these chlorinated mastics that is so good? Why is it they
have become so widely used in spite of their higher cost? What
characteristics do they possess that are not totally desirable
and may make them questionable in the future?
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First and
foremost they are non-flammable. With today's government
constraints, you just cannot use the hazardous, flammable
products of yesteryear on flooring installations.
-
Because of their
non-flammability, your exposure to liability is far less.
-
The elastomeric
chlorinated systems possess most of the key application
requirements such as ease of application, high green grab
(tack), long working time and high strength. They really
have most of the good application characteristics of the
cut-backs plus some added benefits and few of the negatives.
-
They are easier
and cleaner to use.
-
They have
excellent long term aging characteristics if properly
formulated.
They are not,
however, free from negatives.
-
Chlorinated
solvents as a class have some pretty bad actors among them.
Although most of the chlorinated solvents used in adhesive
formulations are relatively safe to use and are not
generally considered a carcinogen by the EPA or OSHA, there
are some blends of 1, 1, I trichloroethane that may be
questionable. To be on the safe side, be sure that your
manufacturer uses pure 1, 1, I trichloroethane rather than
blends in his formulation.
-
Prices continue
to escalate on chlorinated solvents that could eventually
limit the market.
-
The odor is
extremely pungent and you must use adequate ventilation and
air circulation while in use.
-
Under certain
conditions, without adequate ventilation, air circulation,
and the extinguishing of all flames in the area, they can
create an atmosphere that will be corrosive to metallic
surfaces throughout a home or structure.
-
When used over
existing vinyl floors, they can cause a migration of
plasticizers between the vinyl floor and the mastic, that
will not permit the mastic to set up. This problem is
avoided by using primers designed to provide a barrier
between the mastic and the vinyl floor, as well as an
improved bonding surface. Incidentally, this is not peculiar
to only chlorinated mastics. Migration can also occur with
emulsion formulations over vinyl.
At the present time,
chlorinated mastics are the most widely used in the industry and
will continue to be for the immediate future.
What will replace
the elastomeric chlorinated systems and be the product of the
future? The basic technology is already in place and being used.
It is similar to that used in the emulsion polyvinyl acetate
(PVA) systems. The future may be in the development of emulsion
polymers that can be adapted to wood flooring applications of
all types, even though they are water based. After all, we are
already doing this with the PVA emulsion products on finger
block installations.
Hey! Wait a minute!
Are we getting too technical, or what?
What does this wood
floor industry of ours want from a mastic, and how must it work?
We want mastics that are:
-
Safe to work
with.
-
Keep a floor
down forever under normal conditions.
-
Less expensive.
-
Fast and easy to
complete the jobs.
-
Compatible with
a moisture barrier over concrete slabs.
-
Not going to
overstress the substrate as the wood expands, yet return a
shrinking floor.
Mastics must work by
holding the floor with a dry, elastic, "stretchy" bond. The
original roofer used asphalt that turned brittle, then as the
wood changed dimension during season changes, the floor popped
loose. The same is true for rigid/ stiff epoxies today. Even
though extremely strong, as the wood moves the substrate
fractures and there goes the floor. Cut-back asphalt holds the
floor by suction and lets wood move or "float," but we've
already covered the problems of this adhesive type. The mastic
when spread must hold the bead of a notched trowel to insure
positive contact with the wood when used over a less than
perfect subfloor (all of 'em).
There are several
other types of adhesives out there at this writing, namely:
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Contacts that
either are solvent-laden and dangerous, or water-laden and
can destroy the wood. With both you must coat both surfaces,
let them dry, then position the piece perfectly the first
time!
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Polyurethane's
that are strong, elastic, age well and are water resistant,
but are sometimes toxic, always costly, and difficult to
use.
At this point in
this study you can see how today's chlorinated solvent adhesive
meets so many of our needs. The qualities of "strong," "dry,"
"elastic", "bead-holding" all apply and sound like rubber.
Rubber sounds like "latex." Latex emulsion sounds like a mix of
rubber with solvent or water. Solvents sound dangerous and
expensive. Water sounds inexpensive and safe.
Thus we have come
full circle, back to our crystal ball. The adhesive system of
the future will be a water emulsion latex designed to eliminate
warp and grain raise of wood floors. Needless to say, the
adhesive and chemical manufacturers have a tough assignment! But
realize that we no longer must set fire to an asphalt trailer --
and we have walked on the moon!
Another major
consideration in the future will be waste disposal, particularly
containers. The old fashioned trash man or garbage man will
truly become a "waste engineer. As a matter of fact he already
is one. Many of these waste collectors have been trained to keep
their eye open for dumpster disposal of hazardous materials and
they are notifying the EPA when they find them, resulting in
some very costly situations for everyone involved.
Picture if you will
the large volume of all types of adhesives used in just flooring
applications on a high rise office building. Disposal of
sometimes thousands of empty containers is getting to be a major
problem. The problem is even greater when the mechanics fail to
thoroughly wipe out the pails before disposal. We are about to
see s o me major changes in packaging of all types of products
in industry, particularly those containers that originally held
products that even remotely might be considered hazardous waste.
New containers and
new products will also generate new methods of application for
adhesives of all types. Higher labor costs will also ultimately
dictate that more mechanically applied systems be developed to
accommodate all of these changes.
The 1990's brought
many changes and innovative ideas to the wood floor industry.
The installers of the future must remain open minded and be
willing to participate in these new ideas. At the same time they
must remain honest and practical, keeping in mind that they have
an obligation to provide their customers with the best and
highest quality installation possible. Always deal with well
known, reputable suppliers and don't try to be penny wise and
pound foolish by taking unnecessary risk with lesser quality or
lower cost materials. Protect yourself and your customer by
following the recommendations of the manufacturer. Be willing to
try new ideas.
Today's technology
has formulated parquet and engineered wood flooring adhesive
that are Solvent-Free, VOC-Free, and non toxic. With fast
setting formulas, no tack and flash time for the installer. The
latest of these products include such characteristics that not
only include solvent-free high-tack, premium pressure sensitive
wood flooring adhesive specially designed for the installation
of pre-finished engineered wood flooring and parquet. Some are
acrylic-based adhesive specially designed for the installation
of the new pre-finished engineered wood flooring and
pre-finished wood parquet over approved interior substrates.
Easy to spread. Excellent initial grab and high bond strength.
There is also a solvent-free, two-component polyurethane
adhesive specifically also designed for the installation of
pre-finished engineered wood flooring and parquet over quality
underlayment surfaces. Many product now have high solids, are of trowel grade,
water-based synthetic adhesive developed specifically for
installation of wood flooring. For use on, above or below grade.
Allows for normal expansion and contraction of wood floor. Most
have a Good initial grab and firm-setting. Excellent water
resistance. Low VOC, nonflammable and easy water clean-up.
Interior uses only
