By Craig DeWitt
 

The Problem

I frequently see cupped floors during summer’s high humidity levels, but in this case, there was a different problem. The solid wood floors cupped as a result of a dishwasher leak, and then the replacement floors also cupped, which is when I got involved.

The Procedure

The 2-1/4-inch solid red oak flooring in the kitchen and adjacent dining room was removed due to water damage from a leaking dishwasher. The flooring was removed on a Friday and fans were run above and below the area during the weekend. Insulation under the floor was removed to help speed the drying. On Monday, the new flooring was delivered and installed. Within one month, cupping was observed in the replacement 3-inch red oak flooring near the dishwasher area. Over the next few months, the cupping spread throughout the kitchen and dining room. The dishwasher hadn’t been reinstalled, so that wasn’t contributing to the problem.

The Cause

Wood is hygroscopic, meaning it will absorb or release moisture in relation to moisture in the surrounding environment. The absorption of moisture from the air is relatively slow compared with the absorption of liquid water. In this case, the water leaking from the dishwasher was absorbed by the wood floor, resulting in severely cupped flooring. Once the plumbing leak was fixed and the flooring removed, the subfloor and surrounding area could dry. Removing wet insulation from under the floor also helped speed up the drying process. Water in the subfloor evaporated into the house, and potentially into the crawl space. Two things went wrong with the new floor installation. First, the floor was installed as soon as it was brought to the site.I found no evidence of checking to see if the new flooring was at a compatible moisture content with the house or the subfloor. Using a pinless moisture meter, I found that the new flooring was indeed wetter (and therefore larger) than expected for the inside conditions. I also used a pin meter and found subfloor moisture levels as high as 26 percent beneath the dishwasher area where insulation had been removed. Under the dining room, I found subfloor moisture levels of about 16 percent. Extremely tight joints and elevated moisture levels told me that the flooring was absorbing moisture from below. An engineer sent by the insurance company concluded that the crawl space was too damp and caused the new floor to cup. I agreed that the floor did indeed cup because the crawl space was too damp, but I also concluded that the crawl space had been damp for a long time, yet the old flooring had not cupped because it had been properly acclimated to the higher moisture conditions. Another contributing factor was that the wider replacement boards were more prone to cupping than the original, narrower boards.

How to Fix the Floor

Two options are available for fixing this floor. First, getting the crawl space moisture under control will get the subfloor moisture under control. Once the subfloor moisture is at acceptable levels, the floor should flatten without the need to touch the floor, or at worst, it would need a light sand and refinish. From a homeowner’s standpoint, this is the most desirable option. This crawl space was damp enough to promote mold growth, and nearly wet enough to sustain decay fungi, so drying the crawl space would be good for the house, regardless of the floors. The second option is to live with the humid crawl space and deal with the floor. A sand and refinish job would flatten the floor, but may result in excessive gaps and crowning in the winter. The best solution, if leaving the crawl space alone, is to replace the floor with boards that have been properly acclimated to the house’s environment.

In the Future

When replacing flooring that has been damaged by water, make sure the surrounding area is sufficiently dry. This may take more than a couple days of air drying and may require a dehumidifier. In any case, measure the moisture content of the subfloor.it should be near the moisture content of other interior wooden items not affected by the water. If a wooden cabinet door measures 8 percent moisture content and the subfloor measures 15 percent, you are not there yet. Next, make sure the flooring is at the proper moisture content. NOFMA and NWFA guidelines say that the difference in moisture content between the subfloor and solid flooring should be no more than 4 percent. Finally, if you are dealing with a crawl space where insulation was removed from under the subfloor to help speed drying, make sure the insulation is replaced. The insulation helps control floor temperatures and can help avoid nasty condensation- related problems.

Craig DeWitt, Ph.D., P.E., is president of RLC Engineering LLC in Clemson, S.C.

Paul Laurenzi of moisture-meter manufacturer Delmhorst Instrument Co. in Towaco, N.J., also contributed to this article.