A common misconception about lumber is that once it is dried it is permanently cured in its final dimension. In reality, however, a dry piece of wood will exchange water molecules with the surrounding air according to the level of armospheric relative humidity. Subsequent gain or loss of moisture in dry lumber or wood products may cause such troublesome results as shrinking and swelling, interference with proper paint adhesion, and increased susceptibility to stain and decay. A basic understanding of wood-moisture relationships is therefore essential to avoid annoying or costly problems with wood and wood products.