SOMERSET TECHNICAL SERVICES BULLETIN: 2011.8.4

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Cupping (long edges curling upward across the width of each piece) is caused by a moisture imbalance through the thickness of the individual pieces, usually excess moisture on the underside of the flooring. This moisture is coming from various sources include wet subflooring, damp basements/crawlspaces, and humidity due to lack of adequate HVAC control. (Cupping may also occur in excessively dry environments or when exposed to excess heat; the imbalance in this case results from a lack of moisture on top rather than excess moisture below.)

Cupping occurs after the flooring is manufactured, and is not a result of improper drying of the flooring at the mill. After months of air and kiln drying, Somerset lumber acclimates for several days. It then passes inline moisture meters that check every piece as it enters the flooring mill. There are also numerous spot checks throughout the flooring manufacturing process. Any moisture imbalance in the lumber would cup before flooring production started, so “wet” lumber virtually never becomes flooring.

Cupping is beyond Somerset’s control, and therefore is specifically excluded by our warranty. Our installation and floor care guidelines address proper handling, acclimation, site moisture testing, installation, and maintenance of our products to help avoid cupping, among other problems. Installation guidelines are on/in every carton of product we ship, and all Somerset information is available on our website at www.somersetfloors.com.

Several technical documents by industry trade groups address cupping, its causes,
and solutions in detail. These documents include:

• Problems, Causes, and Cures; National Wood Flooring Association (C-200)
• Wood’s Acclimation; National Wood Flooring Association (A-100)
• Cupping and Crowning, National Wood Flooring Manufacturers Association
• Behavior of Flooring and Moisture, National Wood Flooring Manufacturers Association

The solution to cupping begins with proper job site evaluation, including moisture testing and permanent recording of the data, acclimation, installation, and finally proper maintenance of any flooring installation.

Note: Cupped flooring will often “relax” and subsequently perform well if the sources of moisture that caused the cupping in the first place are corrected. Only after the cause of cupping is resolved should any corrective action (board replacement, sanding/finishing, etc.) be considered.