Behavior of Flooring

Most complaints concerning hardwood flooring are related to changes in the moisture content of flooring and surrounding wood products. When moisture changes are severe, the result can be cracks, movement, cupping, and/or buckling of the flooring. Also, a combination of these results may be present in the same floor.

The following information and comments should help explain some causes of shrinking and swelling, and some of the possible results.

WOOD
is an hygroscopic material. When exposed to air it will dry or pick up moisture until it is in equilibrium with the humidity and temperature of the air.

MOISTURE
absorption causes wood to swell.

MOISTURE
loss causes wood to shrink.

SHRINKAGE
begins at 25-30% moisture content, the fiber saturation point. Shrinkage continues to 0% moisture content, an oven dry state.

SWELLING
occurs as wood gains moisture. Swelling occurs from 0% ro 25-30% moisture content, the fiber saturation point.

WOOD
does not shrink or swell equally in all directions.

WOOD
changes approximately 0.1% along the grain (longitudinally), 2% to 8% across the grain and across the annular rings (radially) when quarter sawn, and 5% to 15% across the grain and parallel to the annular rings (tangentially) when plain sawn.