Q. I had standard 2-inch wide maple flooring put in our house. Now, almost every piece has developed a little cupping with the edges high enough that it feels like a corrugated surface. What is going on?

A. First, we know this is a moisture issue, as wood does not change size or shape unless the moisture changes.

One of the keys here is that every piece is cupping upwards. The natural tendency is for wood to cup toward the bark. Because it is likely that the pieces of your floor have random orientation, rings or grain running up or down, if your problem was caused by wet flooring, we would see cupping both up and down. So, in your case, with the cup up, we know that the humidity in the room is drier than the humidity underneath the floor. It is most common that it is the bottom side that is too damp.

When the bottom is damp, the bottom side tries to swell more than the top. Further, the moisture increase causes the strips to swell in width, but there is no room for expansion, so right at the joint, the wood pushes up slightly, exaggerating the cupping appearance.

If you sand and refinish the floor smooth now, it will likely stay flat, unless the humidity underneath increases. Anything you can do to achieve uniform humidity, top and bottom will help. Also, putting a finish on both top and bottom faces prior to installation will also help.

 

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