Editor’s Note: The following article is taken from the Fall 2016 issue of FCICA’s The Flooring Contractor.
View the full issue at: http://digitaladmin.bnpmedia.com/publication/?i=336131.


When it comes to installing hardwood floors, the right adhesive is crucial to a job well done. During the installation of a solid nail-down wood floor, it is common practice to “glue assist” in areas such as starting and ending rows along with borders. When installing wide plank flooring, the flooring industry recommends the use of adhesive in addition to nailing. All-purpose construction adhesive is commonly used for this important installation method due to its convenience and availability at the box stores; however, the short- and long-term drawbacks of using construction adhesive are clear. Save the hassle by implementing these best practices for adhering wide plank flooring.

First, keep in mind that all wood floors are under a fairly constant state of shrink and swell due to factors like seasonal changes in the percentage of relative humidity within a home, yet many DIY construction adhesives are designed to create a rigid bond. An adhesive without elongation properties (to account for the shrink and swell) can allow the flooring to dislodge due to shear stress. This is where using adhesives specifically designed for solid wood flooring installations for a glue assist application is critical for success.

Solid wood flooring adhesive manufacturers, whether offering urethane or silane, will generally publish both the shear strength of the product (expressed as psi) as well as the elongation rate (expressed as a %) to assist in determining which product will provide the right balance of strength and flexibility. Because of the natural shrink and swell of hardwood floors, a solid wood floor is going to experience a wide range of environmental movement. An adhesive manufactured specifically for wood flooring installations can adapt to these environmental changes and maintain the necessary degree of adhesion.

The application method for accomplishing this important step when installing wide-plank flooring has been made even simpler. Several manufacturers produce solid wood flooring adhesives in 20-ounce aluminum foil tubes or “sausages” (about twice the size of a standard adhesive cartridge). This packaging offers minimal waste compared to construction adhesive cartridges packaged in cardboard (which is more susceptible to hardening after being exposed to moisture once opened). Additionally, the applicator guns that house the foil sausages are more ergonomically designed than a standard caulking gun, making a glue assist easier to complete.

Also important to the process is determining how quickly the floor needs to be back in action. Chlorinated solvents were once the adhesive of choice in the mid-1990s and it was absolutely necessary to allow the adhesive to flash off prior to installing the wood. Most of today’s wood flooring adhesives, whether urethane or silane, are installed in a wet lay manner. If there are no concerns that boards may get shifted out of place from “light foot traffic” during the installation timeframe, then an adhesive with a longer open time will be suited for that application. If the flooring will be subjected to “normal foot traffic” during the installation period, or the flooring needs to be sanded and finished soon after completion, then an adhesive with a shorter open time will be better suited for that application.

Generally speaking, the longer the open time the longer it will take the installed flooring to reach full cure. When the floor reaches full cure the room can be back into service or—in the case of an unfinished installation—the professional flooring contractor can get back on top of the floor with sanding machines that will create a degree of vibration through the floor without risk of breaking the bond.

A key advantage of moisture curing silane technology is the ease of clean up on the surface of prefinished flooring. Many new wood flooring installations use prefinished wood which elevates the need to use adhesives that will not mar or chemically etch the prefinished surface. Silane technology makes clean up easy but also doesn’t sacrifice shear strength. Several brands offer high psi ratings that may even rival those of urethanes, while also providing elongation (which is beneficial to the natural shrink and swell of hardwood floors, as mentioned earlier).

Remember that all-purpose adhesives are not designed to do all things. When adhering a hardwood floor, and particularly when completing a glue assist on a wide plank floor, make the determination to use the right adhesive. Your project will have greater success and the floor will last for years to come.