Moisture content of wood

Wood on a live tree contains moisture to keep it alive. After the tree is cut, it begins to dry and then shrink in thickness or diameter. The length will usually stay the same. This shrinkage happens to all woods, no matter what kind of tree it is.

In a live tree, the moisture content can be as high as 200 percent of the weight of wood substance. Shrinkage usually occurs at 25 to 30 percent moisture content. When the tree is cut and the wood is processed to be sold and used as flooring, for example, the moisture content is brought down to zero percent.

A leak or flood causing water damage to the wood will increase its moisture content. The increase in moisture from zero percent to 25-30% - the fiber saturation point - will make the wood swell. Extreme water damage will cause cupping, crowning, buckling, or cracks/splits in the flooring.

Cupping, crowning, and buckling

Cupping is when the edges of a board of wood are higher than the center, forming a concave shape. This is usually caused by moisture imbalance on the wood, where some parts have more moisture content than the others.

Crowning is the opposite; the center of the board is higher than the edges. Crowning occurs when there is excessive moisture on the top of the floor. It can also happen if the floor had cupped during a previous water damage incident, and was sanded before it had dried completely.

Buckling of floors is when the flooring literally pulls up from the subfloor and lifts up several inches in one or more places. This usually happens when the floor is submerged in water for some time.

Remedies

When water damage occurs on wood, the moisture must be removed immediately. Drying may be done with fans and dehumidifiers on top of the floor and if possible, below the floor system such as on the crawlspace. If there is forced air heat in the home - through a heater or furnace, for example - the heat should be turned up to between 76 and 80 degrees F in order to dry the wood. Once the wood is dry, restorative procedures such as screening, filling, recoating and refinishing may be done.

If after the water has been removed the cupping of the wood is prominent but there is no buckling, the wood should be sanded lightly across the grain to remove the wood finishing. This will allow the excess moisture in the wood to dissipate faster. The floor should then be dried, again using fans and dehumidifiers, and then refinished.

Wood that has cupped and buckled indicates that there is excess moisture in the flooring and the flooring system. This excess moisture under the flooring system should be completely removed. When both the floor and the flooring system are completely dry, the damaged areas and loosened areas should be replaced. If there is plywood under the flooring and the plywood was wet by the leak or flood, the entire system should be removed and replaced.

Cosmetical repairs - simply re-nailing, sanding and refinishing - without completely drying the flooring system underneath may result in problems later on. The flooring could develop staining, crowning, finish failure, cracks and become loose. If these problems developed after you have filed your insurance claim for water damage, the cost of repair would have to come out of your pocket and may be more expensive than the payout you got from your insurance company.

Water damage on wood is time-consuming to repair. Quick action is important to arrest further damage. When it comes to restoring the wood and you do not know what you are doing, leave it to the experts and save your wallet from additional unnecessary expenses by letting them do the professional work.