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The Problem
A homeowner called me because the 1,800 square feet of factory-finished kempas flooring that had been recently installed throughout the main level of his 14-year-old Midwestern home had cupped, and the installer was insisting that there was a moisture problem in the home.
The Procedure
Existing floor coverings, including some solid wood flooring, were removed, and the new solid 3/4-by-3 1/2-inch floor was nailed down over the existing plywood subfloor and asphalt felt paper at the end of January. According to the installer, the moisture content (MC) of the subfloor was 9 percent and the MC of the kempas was at 8 percent at the time of installation. About seven weeks later, as spring was underway, the cupping became noticeable. The installer came back, took moisture readings showing 9 to 10 percent MC in the subfloor and 12 percent MC in the kempas, said there must have been some moisture introduced to the floor and told the homeowner to wait for it to settle back down. The cupping continued to worsen over the next several weeks, and the floor began to buckle. The installer returned in July, took a moisture reading showing 10 to 11 percent MC in the subfloor and 15 percent MC in the kempas. He again insisted there was a moisture problem in the home. At that point, the homeowner called me.
The Cause
At the home, I could see significant cupping throughout all rooms with the kempas, and there was no indication of a moisture source. My readings showed a normal subfloor MC of 10 to 11 percent and 9 to 10 percent in the kempas. The home's temperature and relative humidity readings were also normal. There was a full carton of the kempas flooring stored in a closet in the finished basement. Measurements of this unused flooring showed it to be exactly on size— 3/4 by 3 1/2 inches, with a MC of 9 to 10 percent. I racked out 10 rows of the unused flooring, which also was exactly on size. I then compared the width to different areas with 10 rows of installed flooring, revealing that 10 rows of the installed flooring was 7/16 inch narrower than the uninstalled flooring.
At this point, all evidence was pointing to the flooring having been installed at a MC that was too low, but the installer said he had carefully recorded his moisture readings, which looked perfect. He said his readings were taken from the analog display on the face of the meter. In my inspection kit I have the same pinless moisture meter he had used; it comes with a species adjustment table showing how to adjust the readings for the average specific gravity of different species. This chart showed that when the moisture meter read 8 percent, the MC of the kempas was actually an average of 4 percent, and when it read 15 percent in July, the actual MC was 9.5 percent. The flooring was currently at an acceptable MC, but it had been installed after being acclimated to the driest seasonal extreme.
How to Fix the Floor
For the installer, this turned out to be an expensive lesson on correct use of a moisture meter. Because the cupping was not going to go away with seasonal changes and the floor was buckling, he had to replace the floor at his cost.
In the Future
Although many installers have become more aware that they need to use moisture meters on all their jobs, just using a moisture meter isn't enough. Each moisture meter is different and must be used correctly. With all the exotics being used today, knowing how to adjust the readings to get the true MC results is more important than ever.