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The Problem
A builder contacted me about unusual separations that began to appear at random head joints in a floating wood floor two-and-a-half years after installation. Although the condition was not extensive, the separations were quite noticeable, measuring 1/8 to 1/4 inch in width.
The Procedure
The floor was in a large exercise room in a multimillion-dollar residence. Due to the very dry climate, a specialized HVAC system had been designed so the interior would be consistently between 66 and 70 degrees Fahrenheit and 40 to 50 percent relative humidity. The wood flooring was a 9/16 -inch solid, two-stave, tongue-and-grooved imported product. The staves were connected by a glued dovetail joint. Each stave measured 2 1/2 inches wide, producing a 5inch-wide face. The average stave length was 25 1/2 inches. A combination of full- and partial-length staves were joined by the manufacturer to produce an overall board length of 6 feet. Because of the end use as an exercise floor, the architect had specified a floating installation over foam underlayment utilizing a metal clip system. The subfloor was an on-grade concrete slab that had been properly tested for moisture before installation.
The Cause
Upon inspection, I noticed the separations were not at the tongue-and-groove head joints, but rather at the stave head joints within the boards. The installer had correctly glued the head tongue-and-groove joints as required by the manufacturer to prevent board movement during normal use. Measurements taken of the individual staves in each affected board indicated they were on size as manufactured with no discernible change in dimensions. This led to my conclusion that the gaps were caused by insufficient adhesive application during the manufacturing process. There was enough adhesive for initial holding power, but with foot traffic over time, the floor began to fail.
How to Fix the Floor
The condition was isolated to a few areas and involved only seven boards. Since the floor was installed as a floating system with clips, board removal and replacement was relatively simple and was covered by the manufacturer's warranty.
If the problem had been extensive, then removal of the entire floor may have been necessary. Careful removal of the floor would permit reinstallation, either by nailing or gluing down to an appropriate subfloor. Both of these methods prevent movement along the dovetail joints even if they were insufficiently glued when manufactured.
A specialized expansion strip from the manufacturer can also be installed around perimeter walls and vertical obstructions where the head joints terminate. The strip does not allow the staves to move along the board length. This technique is only used when the product is installed as a floating floor.
In the Future
For this floor, a simple test prior to installation would have indicated whether the dovetail joints were properly glued when manufactured: Movement of the staves would have been detected by placing an individual board on end and carefully tapping it on the floor. Of course, it is unrealistic to expect an installer to take the time to test all the boards. The proactive approach would be to simply install the expansion strip when a floating installation method is used for this type of product. As the number of imported wood flooring products increases, it is imperative that the contractor fully understand the product before installing it.