Wood Floor Smoothness Changes

Moisture-related movement can cause wood floors to move and become rough at the joints. February 23, 2010

I installed a regular old 3/4" x 1 1/2" plain sawn red oak. It was the middle of the summer of 2007. The house was built 10 years ago and the subfloor was flat and the moisture of the subfloor was 11 percent. We installed the floor and immediately started sanding and finishing it.

About three months later I get a call from the home owner and he wants me to look at the floor. When I went there I discovered that 10 % of the boards had somehow raised up on the tongue side to have over wood again, about the thickness of a business card. It was always on the tongue side of the board. I have had other professionals look at it and no one has an answer. Any words pertaining to this would be much appreciated.

Forum Responses
(Architectural Woodworking Forum)
From contributor J:
Can you clarify "raised up on the tongue side to have over wood again?" I don't understand what you mean by this.

From contributor U:
Was there a moisture barrier put between the subfloor and the new floor? What is below that floor -a basement, etc? What was the moisture content of the wood when put in place? Was the flooring allowed to acclimate to the inside conditions of the house at the time for about a week or longer? There is a lot that could have happened here. What is the total amount of slop in the joint area of the tongue and groove. Is that consistent in all the pieces?

From contributor K:
I think contributor R has identified what could be the problem. Despite the 11% reading off the subfloor, did you do a moisture test anyway? I've known situations where the moisture content, as read, of the subfloor has actually only been that of the top inch or so, revealed by the simple expedient of taping a foot square piece of polythene down and leaving it for a day or two. If it comes up positive for moisture then a vapor barrier is laid down.

The fact that the compression indication is on the tongue side in all cases means nothing in itself, but I'm surprised the expansion hasn't manifested itself in even the slightest lifting of the boards.

Was it a floating floor or fixed? How much of an expansion gap did you leave all around? The fact that it was fitted mid-summer 2007 with no problems since does add to the mystery, but perhaps you need to ask yourself what sort of weather conditions have prevailed in the last few months? Also, perhaps related to that, has anything happened to affect the subfloor in the interim?

From Gene Wengert, forum technical advisor:
This is common for dry floors that are tightly installed and then are subjected to moisture regain. As the moisture increases and the wood then swells, there is nowhere for the wood to go, so it raises up a bit. If you sand it now, it will be flat, but when the floor dries out a bit (if it does dry out; when the heat comes on perhaps), there will be some small cracks between the pieces.