Hardwood Floors February/March 2019

By Brett Miller

in to play, builders are moving to OSB for their new construction subfloors. OSB can be a good subflooring option, though different performance levels exist. The wood flooring industry has bemoaned the use of commodity OSB products due to swelling after exposure to the multiple wetting/drying cycles experienced during the build. We know that swelling can occur with any wood product when exposed to water. In OSB, this swelling can create a decrease in fiber density and a degradation of bond strength between the strands, especially at panel edges, causing a reduction in wood flooring fastener retention. The loss of fastener holding can directly impact the performance of otherwise properly installed engineered wood flooring. RECOMMENDED FASTENERS The recommended fasteners used when installing engineered products are normally 18-20 gauge cleats or narrow crown staples anywhere from 1" to 1 1/2" in length. These types of fasteners require a much tighter fastener schedule than the heavier gauge, longer-length fasteners used to install 3/4" solid and engineered wood flooring. In general, for engineered flooring, fasteners should be placed every 3"-4" and within 1"-2" of the ends of each plank (unless otherwise suggested by the flooring manufacturer). The truth is, 1" fasteners used to install engineered wood flooring only penetrate the subfloor 5/16" (for 5/8" flooring) or 1/2" (for 3/8" flooring), and when used over the previously wetted OSB subflooring, they have very little to hold on to.

Following are a few of the more common causes of squeaking, popping, and crunching noises in installed engineered wood floors. SUBFLOOR FLATNESS The NWFA standard for subfloor flatness on a nail-down installation is 1/4" in 10' or 3/16" in 6'. When subfloors are outside of the flatness tolerances, voids are created that allow the flooring to move vertically, resulting in a noisy flooring system.

WIDER PLANKS The trends have been continuing to move toward wider planks. Wide plank installation poses new challenges. Wider planks result in fewer fasteners per square foot. Consider how many fasteners are in any given square foot of a properly installed engineered wood floor that has been nailed at 3"-4" intervals: • between 12 and 16 fasteners per square foot on a 3" wide plank; between 6 and 8 fasteners per square foot on a 6" wide plank; and • More fasteners are not always feasible. Alternative installation methods such as full-spread or glue-assisted installations are sometimes a good alternative option. These options over wood subfloors are only acceptable when moisture is 100 percent controlled from below the flooring system. Further discussion on this topic is one for another article. OVERDRIVEN/UNDERDRIVEN FASTENERS It is not uncommon for a crew to use an undersized compressor or to have several nailers running off one compressor at a jobsite. Without an individual regulator on each hose, the compressor will not be able to deliver air pressure consistently to each nailer throughout the installation. To compensate for this, some crews will turn the PSI up on their compressor. This causes too much air being delivered to the nailer when the tank is full, resulting in overdriven • between 3 and 4 fasteners per square foot on a 12" wide plank.

It is almost always necessary to expect that the subfloor seams will need to be sanded flat as part of jobsite preparation. When the subfloor seams are not sanded flat, the result is normally a subfloor that is not within tolerance. Subfloors that are not properly scraped or cleaned before installation can also cause similar voids or high spots that can result in a noisy floor system. Dried globs of drywall mud, paint, grout, or other construction materials not adequately removed from the subfloor will also adversely affect the flatness of the substrate and result in a noisy floor. OSB SUBFLOORING As the availability of slow growth plywood fades and economics come

the magazine of the national wood flooring association

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