Cupping caused by off/on air conditioner?

Q: We installed a hardwood floor with professional installers (sanded and finished) over a large span of time, the first of May. The wood was in the house for five weeks before being installed. The customer called the second week of August to say the floor was cupping. Upon inspection the centre of the area is cupping but perimeter is not.

The top surface had a reading of 12%, while the underside read 8%. I surmise they used water to clean floor, but customer denies they used water. Is there any other explanation?

A: This is not an easy job, is it? Maybe when floor guys get their heads together a problem can be figured out. Floormasters is another good source. I think, given the amount of time the wood was in the house and the amount of time before the floor cupped (3 months) really means this problem is something you caused. I have seen jobs near large bodies of water for example, where the floor was not acclimated. It was taken in, installed, sanded and finished. Within a few weeks it cupped. This job is 3 months. I am not so sure cupping indicates excessive water use in cleaning. You would more likely find crowning, where the surface is wet and the underside of the board is more dry, so it crowns with the centre of the board raising, and the edges lower. Is it possible there is a leak from above, running down a wall and under the floor? Yes, I know the underside is normal reading, but how long have they waited to call you since the cupping started? There can be only one explanation for cupping and crowning:excessive moisture. Finding the source is the tough part. Did the installers check the sub floor and the hardwood before installing to make sure it was within limits? That is 4%? If the sub floor in the centre of the room had gotten wet for some reason and they put the floor down on top of that, the result would be what you see. There has to be a reason why the middle is cupping and the edges aren’t. Still, if the sub floor was wet it would not have taken 3 months for the cupping to happen. Just thinking out loud.

Follow-up Q: If the customer turned off the air conditioning during the day and turned it on when they returned, would that cause cupping wood floors? The outer perimeter, a water closet and small hall, have no cupping. Could it be caused by not running the air conditioner and the moisture builds up and falls to floor when air conditioner is then turned on? I also read that a new home contains about 500 gallons of water from all the new materials to construct the home.

The wood sat in the home for at least 4 weeks prior to installation, the last two weeks with heat on since it was cold.

A: I think it could easily be cupped because of high humidity in the home. If it was installed at say 40% relative humidity, and that is what it was acclimated to and then the count goes up to say 84% that would be more than double the amount of airborne moisture and the floor certainly absorbs and releases this. It would be interesting to leave a hygrometer on the floor in the cupped area and see what the readings are, especially during the day when the air is turned off. I would put this down to an environmental issue.