Due to the proliferation of exotic hardwood species on the market today, adhesive makers have had to adapt, developing glue systems that perform 
consistently and effectively despite higher density product and sensitivity to moisture. Using state-of-the-art technology, they are making life easier for mechanics and, ultimately, end users.
According to Bob Swezey, technical director for Stauf, there have been significant changes in wood adhesives recently, specifically around moisture barriers and the many new exotic woods. Leading manufacturers now offer “one- or two-step adhesive systems that allow the application of a moisture barrier at the same time the adhesive is being spread. This results in faster installation times and has been an effective deterrent to the greatest enemy of wood floors: subfloor moisture.”
Like Swezey, Gary Liddington, business manager, manufacturing brands for W.F. Taylor, believes the tendency of exotic species to be more affected by moisture than common domestic species that require higher strength and low (or no) moisture wood flooring adhesives. “Modified silane wood flooring adhesives are rapidly becoming the adhesive of choice over traditional urethane adhesives, not only because of their high strength and zero solvent and water content, but because of their low VOC emissions, which makes them a much better environ- mental fit than urethanes.”
Christine Krisko, marketing communications manager for Bostik, believes adhesives have improved over the years relative to all wood species. “They’re 
easier to trowel and hold ridges better than ever.” But she also believes urethane-based adhesives still have a place in the market today as they “have the right balance of physical properties while adhering to any species of wood. They are flexible enough to allow the wood to expand and contract with the environment and ridged enough to keep the floor securely together, fill in gaps and accommodate for normal subfloor variation.”
John Lio, marketing manager for DriTac, noted wood flooring adhesives today have far more expanded roles than ever before. In addition to bonding wood flooring to a subfloor, adhesives are now offering moisture vapor control, sound control and crack suppression.
“Exotic species are more sensitive to moisture and temperature changes than domestic woods,” he said. “The new adhesives on the market today offer protection from moisture and help control expansion and contraction due to moisture from the substrate. Many foreign manufacturers also apply sealer to the back of their finished wood products to help stabilize the moisture intake. It is because of this that adhesive formulas have had to adjust to bonding sealed and slick finish surfaces.”
However, Joe Tuttolomondo, vice president and general manager of XL Brands, believes what’s happening with wood adhesives today goes back several years to when the National Wood Flooring Association (NWFA) reversed a longstanding position that solid wood floors should be nailed down.
“It made an allowance for gluing down solid wood floors with the caveat that a moisture-retardant barrier was part of the installation.
“NWFA wanted to ensure that slab moisture did not come into play in the installation and ruin the floor,” he added. “That started a revolution in the adhesive business, not the increase of exotic imports. This development also led to newer adhesives that were easier to spread with lower odor levels than previous generations of adhesives, especially in moisture-cured urethanes.”
In addition, Tuttolomondo concluded, adhesives that contain solvents and isocyanates have begun to appear with much lower levels of both components for several reasons, “including environmental, clean-up and etching the finish of pre-finished boards.”
-Louis Iannaco