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The Problem
Recently, I received a call from one of our largest distributors. His customer, a flooring contractor specializing in builder accounts, had made a complaint regarding loose and hollow spots in a recently installed engineered wood floor. Apparently, the subdivision contractor and home builder had both recognized some minor spots upon completion of the installation, but nothing to cause concern. When the homeowners took residence in the new home, however, the spots worsened. The flooring contractor reported that he had drilled and injected the hollow areas, but, despite his efforts, the hollow and loose spots remained, and some actually grew in size. The flooring contractor labeled the situation an adhesive failure.
The Procedure
In this home, the wood flooring was actually an upgrade from the 3/8-inch-thick, 3-inch-wide, three-ply engineered plank often installed in subdivisions. For this particular project, the wood flooring was 9/16 inch-thick, 5-inch-wide, five-ply engineered plank. The installer said he had followed the same procedures he would use to install standard engineered plank over a concrete substrate.
The Cause
After arriving at the job site and visually inspecting the wood flooring system, I noticed the floor's multitude of loose and hollow areas. The flooring contractor and I removed several boards over the hollow spots. We then used moisture meters to gauge the level of moisture on the concrete. The readings from the meters confirmed that the moisture level met the requirements of both the wood flooring and adhesive manufacturers.
However, when we proceeded with inspection of the boards themselves, we discovered that very little adhesive had transferred to the back of the boards. Also, measurements from a laser level and tape measure determined that the concrete substrate had high and low spots measuring up to 3/8 inch in the problem areas. In addition, large amounts of paint over-spray, drywall compound and other contaminates were visible on the concrete.
After we completed the inspection, it was evident that the adhesive was not the reason for the floor failure. The floor failed because the installer did not take into consideration that thicker and wider boards are much more rigid than traditional thin and narrow boards. Because of this rigidity,the boards would never conform to the concrete substrate variance in this project. In addition, the installer did not recognize that for these wider and thicker boards, a trowel with a different configuration was needed to allow the installer to apply more adhesive and decrease the spread rate per square foot.
When the family had moved into this new home and the floors were subjected to foot traffic, the boards were constantly moving up and down over low and high spots in the concrete substrate. This caused the hollow and loose spots to increase in size. In addition, the paint and debris left on the substrate before the wood flooring was installed resulted in the boards loosening.
Obviously, the failure was not caused by defective adhesive. The hollow and loose spots were there sult of a dirty, uneven substrate and incorrect installation tools and methods.
How to Fix the Floor
In less-severe cases, hollow and loose spots can generally be fixed by drilling and injecting adhesive under the loose boards. But, in this instance,because of the substrate's unevenness and excessive surface debris, it was necessary to remove large sections of the wood flooring. Once the wood flooring was removed, the concrete was cleaned and leveled to industry requirements. The wood flooring was then re-installed using the correct trowel and necessary adhesive coverage as recommended by the manufacturer.
In the Future
It is important for all parties involved in the product specifying process to fully understand the products chosen and the different installation procedures required. Not all wood flooring is installed using a standard adhesive or set amount of adhesive per square foot. In addition, the substrate must be free of all paint, drywall compound, dirt and other materials that might compromise the adhesive bond. With thicker wood flooring boards,more attention must be paid to the flatness of the concrete. The use of pressure-sensitive or rebondable adhesives can eliminate most hollow spots caused by minor irregularities in the concrete substrate. Adhesive injection kits also work when the high or low areas in the concrete are not critical and the boards are flexible. If there are any uncertainties regarding installation procedures, it is important to contact the wood flooring manufacturer or adhesive manufacturer for instruction. Just about all manufacturers have technical service departments. Knowing the facts will save money and stress for all parties involved.