The Cupping 18-Inch Plank (or 'Why I Always Use a Moisture Meter')

A cupping 18-inch-wide Doug fir wood floor.I could not be more thankful that I always use a moisture meter for every wood order, in particular because of this most recent experience.

I went to see a complaint on warping planks for a job I did not eight months previous. The GC insisted I improperly installed the plank and the warping was somehow my fault and responsibility. This is no ordinary plank: It is Douglas fir, 18” wide and 1 1/4” thick with the planks running full length wall to wall. At its narrowest point, the floor is 13 feet wide and at its widest, it’s 21’6”. May I add, it also runs under the drywall for the shadow recess that is so popular here in southern Florida.

When the wood first arrived, I moisture-tested it. It wasn’t ready for my area, and I advised the GC that the wood install had to wait. Not happy about it, he waited. Over several months, I monitored the wood, and when it hit the 10% mark, the wood was ready. It was installed before the drywall because of the bottom recess design, and I remained monitoring the wood up to the point of our finish completion. It remained steady at 10% (as it should be for our area).

Fast forward to today. The GC is looking at the warped planks in the bathroom, hall and master closet (backing up to the bathroom). He is telling me there is no leak. I’m saying there is because the rest of the house is pan-flat. He insists that I did something wrong with the wood install. I’m telling him the only reason wood will cup is from moisture content change—in this house, from a leak! He says no one has seen a leak, there can’t be a leak.

A wet slab showing a leak under a wood floor.Back and forth we go. This wood comes from Denmark—it isn’t cheap by any means—and the wood goes under the drywall. It would be a major undertaking to take out and put back planks, and he doesn’t want to eat it. Well, neither do I.

I hit the plank in the bathroom with the moisture meter … 17%. That’s far from the 10% I put it in there with. So out comes the first plank … and there is the skin of water on the slab. There was so much water the adhesive peeled from the slab.

We took out six boards with a skin of water under all of them, and the perimeter still read in the mid to high teens. He stopped me from going further, still insisting that these readings are “normal” and the cupping is still my fault! He grabs my meter and heads over to the master bedroom. He hits three spots, and all read 10.1%. He had nothing to say after that.

The leak, by the way, came from a faulty washer in the diverter inside the wall of the shower.

Use your moisture meter—always. If you don’t have one, get one, learn how to use it and use it everywhere. It can save you, trust me.