We purchased 3/8" Brazilian Cherry from Lumber Liquidators in the summer of 2007. We took the old floor up all the way to the 2x8 tongue and groove Doug Fir. 3/4" AC (sanded) plywood was then placed on top of the tongue and groove. Then 15# felt tar paper was then placed on top of the plywood. The hardwood was stapled to that subfloor. We are having slight cupping problems that I had begun to notice about 6 months ago. It has gotten worse over the last months. What is going on? I contacted Lumber Liquidators and they indicated that it was a moisture problem. Where is the moisture coming from? We have black plastic on the floor of our crawl space and insulation in the floor. Could you please advise.

Thank you.

take a moisture test of the floor it should not be more then 8-10 %. if it is more you might have a leak. did you acclimate the flooring before you installed it. solid floors should sit it the air for 1-2 weeks. did you take moisture test of the plywood. if the plwood was 20% and your flooring was 7% thats your problem. is there water running under the house from rain runoff?
MARK TSISTINAS

Yes, we let the flooring acclimate for longer than 2 weeks in the house. We do not have any leaks and there is no water under our house. How do you take a moisture test of the plywood?--and if that is the problem how does one correct it now?

CUPPING

According to The National Wood Flooring Association, in their publication, "Handling Complaints/Trouble Shooting Manual, page 7, cupping can only occur when there is a locally caused, excessive moisture condition. Cupping occurs when there is an imbalance of moisture distribution within each board. That is...the bottom of the board absorbs excessive moisture and swells widthwise, while the face of the board, with less moisture content, holds tight, providing widthwise dimensional stability. In this case the weakest point for any movement is at the board's edges. Once the board's edges start to bend upward cupping becomes quite visible. This extra stress and stretching of the board's finish can cause it to become compromised. The results may include objectionable finish problems such as cracking, peeling, flaking, or chipping. In addition, the structural body of the boards can suffer stress fracture splits on the ends or face checking. This is not due to any deficiencies in the wood product. Cupping is locally caused moisture, usually on the underside of the boards. Cupping is never a manufacturing related issue.

The National Wood Flooring Association states that "The only reason a wood floor cups is locally caused elevated moisture, nothing else." As wood is a natural hygroscopic material, it will absorb moisture and expand when the relative humidity or sub floor moisture content raises and shrink, causing gaps between boards, when it loses moisture.