Hardwood floors on concrete? Years ago there was only
one way of doing so. Then it was the "sleeper on slab"
system that involved fastening 2' X 4's to the concrete
laid on their side, as shown in the image below courtesy
of The National Oak Flooring Manufacturers Association (NOFMA).
Prior to installing the sleepers, a poly film and/or #15
asphalt felt is laid over the slab for moisture
protection and installed in cutback mastic.
Finished Floor May Be Too High
While a
subfloor over concrete such as this application is not
widely used today, it creates vertical height concerns.
Final heights are in the 2 1/4" range after the actual
hardwood floor is nailed. This can cause problems with
exterior door entries and other fixed objects. In some
cases 3/4" plywood is used above the sleepers, adding
another 3/4" or a total overall height of three inches
is created. Using this method in new construction, one
should plan well in advance to avoid vertical height
concerns from one floor covering to another.
Better
Method. Plywood Only On Concrete
The most popular method of installing solid 3/4"
hardwood floors on concrete today would be a plywood
subfloor attached to the slab (illustration below and
left). Using a minimum 5/8" CDX plywood, the material is
installed over the same moisture barriers but it is
attached by way of concrete fasteners. A variety of
fasteners are used, including concrete cut nails,
tapcons (concrete screws), and Hilti types. Methods vary
from one region to another, or what professionals are
accustomed to.
 Floating
Subfloors
Other
methods of using 3/4" solid hardwood on concrete would
be "floating subfloors." Yea...really...what's a
floating subfloor you ask? The same moisture barriers
would be used but two layers of 1/2" plywood would be
used. Plywood is installed opposite of one another,
overlapped at the seams, then stapled or screwed
together. The preference here is not to puncture the
moisture barriers with fasteners.
Glue
Plywood To Concrete
If the
floating subfloor doesn't work for you, another method
calls for gluing the plywood direct to concrete. In this
situation a premium urethane adhesive is often
recommended. Keeping the plywood adhered or flat can
cause problems. The solution here is establishing kerf
cuts on the backside of the plywood with a circular saw
giving it better flexing properties.
Solid
3/4" Gluedowns?
In recent
years you may find some of the big box stores have been
advocating this procedure. We only wish them the best,
but have never been fond of this installation procedure.
However, more upscale 3/4" installations in Herringbone
and large parquet patterns have proven successful over
the years. These types involve much smaller pieces that
will not expand and contract as much as more common 3/4"
hardwoods.
Other Methods of Installing Hardwood Floors On
Concrete
In the
past 30 years other applications have proven successful
when installing hardwood floors on concrete. They
include; engineered hardwood floors that basically float
over any sub floor. Instead of nailing or stapling they
are glued by tongue and groove only and float over a
foam cushioned padding. Another popular method is gluing
direct to the concrete subfloor. The glue down of
engineered products should only be considered with those
knowledgeable to do so. It's important to note not all
engineered products can be floated. Always consult the
manufacturers specifications and don't rely on
misinformed salespeople. |
