I looked at a floor this week that fits in with last week's comments. It was a nail-down 3/4" bamboo floor recently installed in a house a friend was trying to buy. And it was cupped. The moisture content with my bamboo-calibrated meter was low to below-low. (The meter says "Low" when it's below 6%. Lower than that I get no reading.) Humidity in the house was 29%, and 31% in the basement.
The flooring even looked like it had actually distorted. It was an "engineered" product made up of two layers of strips about 7/8" wide. The strips were stacked on top of each other, then the double stack was glued side by side to make up a piece of flooring. So glue lines ran from the bottom of the board to the top. The boards had distorted such that the glue lines were visible. Here's a photo:
The installer was not a professional installer. The flooring came from a big box store, and he had followed instructions. In the end, the flooring got installed too dry. A gain of moisture to even low humidity conditions in this house had resulted in cupped and distorted flooring. I would have hated to see what happened to this floor in more humid seasons. The seller has agreed to redo the floor.
