hey guys,
I recently talked to a friend who bought strand (also called "woven") bamboo flooring for their home- living room and two hallways. They glued down to 3/4" ply subfloor. In order to preserve the plank direction from the living room to one of the hallways, the installer decided it would be a good idea to lay the planks perpendicular to the length of the hallway. So, he cut each plank to approx. 4' (the width of the hallway), and laid them from wall to wall. Sounds like a lazy contractor to me...

Now, the planks in that hallway are cupping. The rest of the floor (living room and hallway that has flooring laid parallel to the length of the hall) is fine. No evidence of any moisture issues, and the subfloor is the same throughout the house.

We're trying to figure out why the one hallway cupped. Could it be because the floor is not bound to the rest of the floor via the T&G on all four (or at least three) sides?

The subfloor in the hall had a much higher moisture content, or the moisture retarder was not used under the hall. Another cause can be lack of acclimating the boards in the hall, to a higher moisture content, then when they were laid. They swelled and instead of buckling(which it may still do) it compressed the edges of the boards together, crushing the fiber, and giving it a cupped appearence.

Normal cupping is caused by an imbalance in the boards moisture content from the top of the board, to the bottom of the board. The bottom of the board will be wetter in moisture content then the top. Crowning is just the opposite.