A Perfect Mix: Hardwood Installations Over Concrete
For many years, resistance to change was the norm within our industry. Solid hardwood flooring had long been the King of the Hill. Little, if any, attention was given to the “Lost Valley” of installations that lay below grade. At the time, the mentality of the consumer, which was nourished by the salesperson and/or installer, could be summed up in the arrogant phrase: “Accept no substitutes.”
Understanding the accepted requirements for solid hardwood flooring installations placed an immediate restriction on our industry to capitalize on floor covering market share. On- or above-grade installation requirements left our industry defenseless to alternative floor covering choices.
The notion that “thicker is better” still reigned supreme This perception was actually a misconception -- one that could have become a death sentence had wood floor manufacturers not persevered. Indeed, the writing was on the wall.
The industry had to come up with products that could compete with other types of floor coverings that, by their nature, were suitable for installation in areas where solid-wood flooring installations were doomed due to unacceptable subfloor conditions or transitional problems with adjacent, alternative floor coverings. In particular, what truly spurred wood manufacturers in this effort was the proliferation of alternative floor coverings that imitated the look of genuine hardwood.
Another key factor arose in new-home construction when concrete subfloors, due to geographic location with regard to sea level, became an obvious alternative to the traditional crawlspace concept. Today, construction industry reports indicate that 40 percent of both new and existing residential homes have on-grade concrete subfloors. Basements, particularly in the southwest and southeast regions of the country, practically don’t exist anymore.
This is not to say that solid hardwood floors don’t exist in homes with on-grade slabs. Many owners of these homes enjoy the comfort and value of hardwood floors. That’s because our industry’s marketing limitations were removed with the introduction of engineered hardwood flooring products. These specialty products address concerns related to humidity and moisture, as well as the transition problems that plagued solid-hardwood floor installations.
Another key item of interest to homebuilders was the need for structural integrity. Solid hardwood flooring installed over plywood adds to the integrity of the subfloor. And concrete subfloors definitely surpass those requirements.
For the most part, engineered wood floor products are judged by end users and consumers purely on appearance. Also, the benefits of expediting the installation process by removing the need for additional wood subfloor nailing surface is tough to deny, especially when combined with a cost decrease and an installation productivity increase.
An engineered wood floor performs exceptionally well with the support of its concrete subfloor counterpart. To truly appreciate the value of engineered floors under these jobsite conditions, we need to outline the fundamental requirements for installing 3/4-inch solid hardwood under the same circumstances.
As when any hardwood floor is to be installed, moisture tests should be conducted to determine the dryness of the slab. Concrete normally requires a minimum of 90 days for curing. Qualify the slab for flatness and any cracks that may need attention.
1. Pre-deliver subflooring materials and hardwood floor products for acclimation to environmental conditions that should be suitable for occupancy.
2. The two most common types of wood subfloors that are attached to concrete slabs are 2-by-4-inch treated sleepers or 3/4-inch exterior CDX-grade plywood, or a combination of both. Total elevation from the concrete subfloor to the top face of the hardwood flooring strips can range from 2 3/4-inches for a sleeper-only installation to 3 1/2-inches where a combination of sleepers, plywood and 3/4-inch hardwood flooring strips are used.
Consideration must be given to the adjacent floor covering because transitional strips will be required where the two flooring types adjoin. NOTE: The transition points can be dramatically reduced or even set flush with each other by “recessing” the areas of concrete during the pouring process to accommodate the requirements for the hardwood flooring installation. Treated sleepers can also be installed (dropped) at 8- to 10-inch intervals across the entire area while the concrete is being poured. Opposing wall lines require a sleeper that runs the entire length of the area as well.
3. It’s important that a 4- to 6-mil polyethylene sheet be draped over a secured sleeper-only subfloor installation. Plywood subfloors only require a suitable mastic troweling over the concrete sub-floor. Polyethylene is then spread over the mastic and rolled relatively smooth. Another coat of mastic is then troweled over the poly. Plywood is then “dropped” into the mastic and then concrete nailed or pinned to the concrete subfloor. A minimum of 16 fasteners per 4-by-8-foot sheet of plywood is required.
4. Before installing the hardwood flooring strips over the plywood, I strongly recommend that 15-lb. black roofing paper be loose laid over the plywood as an additional moisture barrier.
5. On plywood-only subfloors with no sleepers, fasteners should be 1 1/2 inches long -- rather than the traditional 2-inch fastener -- to avoid making contact with the concrete subfloor.
Dealers/contractors have been installing solid hardwood flooring on grade for years by successfully utilizing the procedures outlined above. Concrete can be conquered. And with the ease of installation and the mastic-only requirements for attaching engineered hardwood flooring products, you too can be a part of the “perfect mix.”
All we at Wood or Wood Knot asks of you is that you just to try and begin to blend wood with concrete.