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.
Â 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.