Flooring cupping again & again

Q: Twice now we had to have the floor that runs from the rear door to the bathroom (10 x 6 ft.) resanded and restained because it started to cup.

It is now doing it again, the guy says maybe my contractor didn’t install the new rear door correct and either water or cold is getting in under the floor.

A: Fortunately, this cupping has nothing to do with using “poor quality” wood. There is only one thing that can cause this, and that being excessive moisture. This could be from a non vented crawl space under the floor, a leak in your roof, with the water coming down the wall and under the floor. A leak from the bathroom on the second floor, or a leak from your kitchen plumbing or main floor bathroom.

  When the floor was first installed, it would have been a good idea to check both the sub floor and new oak flooring with a moisture meter. There should not be more than about 4% difference between them, with normal for oak being between 7-9%. Since this is only one section of the floor that is cupping, we can probably eliminate any serious difference at the time of installation. You are going to have to isolate where the water is coming from before you ever try to fix the floor. That would be my advice immediately in a case like this, before I ever sanded it.

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  1. Follow-up Q:I don’t know where the “excessive moisture” could be coming from other than the rear door. The kitchen is on the 2nd level with a deck directly outside . The contractor replaced the outside door & frame. He did some extensive caulking all around the door, but I don’t think he insulated or put paper around the frame prior to installing the trim, but I have been told that because my joist run vertical to the door, water/cold air could only go as far as the first joist. The first joist is where the door jam is, so how can an entire section of flooring be cupping if nothing can get by the first joist? I have also read that the floor should have been brought into my house at least a few days prior to installation so it could adjust to the moisture conditions. It was brought and installed in the same day.

    A: It is certainly recommended that the floor be in the house at least 3 days before installation. The sub floor should not have more than a 4% difference in moisture to the floor you are installing on top. However, you say this problem has happened twice, so I would think the issue is another source. I also find it hard to imagine that even if water got past your door, that the damage from that would extend over a long span of flooring. You would have to have a couple of gallons of water come in, I would think. You would know if that was happening pretty fast. If the kitchen is above this floor, I think I would be looking there. Dishwasher, plumbing for the sink.

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