Plywood 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 3/4" 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 Sub floors

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 (trowled) 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.