Longitudinal Water Permeability of Western Hemlock II. Unsteady-State Permeability


  • R. T. Lin
  • E. P. Lancaster


Tsuga heterophylla, sapwood, heartwood, wetwood, kiln-drying, wet pockets


A mathematical model was developed and used as the basis for constructing two experimental apparatuses to investigate the permeability of western hemlock to water. When unsteady-state and steady-state permeability were compared, the unsteady-state permeability of both sapwood and normal heartwood was found to be higher than the steady-state permeability, but that of wetwood was generally lower than the initial steady-state permeability and was of the order of the final steady-state permeability. The permeability of western hemlock to water, regardless of whether it is measured by steady-state or unsteady-state techniques, is the highest for sapwood, followed by wetwood and normal heartwood.

Under unsteady-state conditions, sapwood permeability is time-independent, but wetwood exhibits time-dependent behavior, probably caused by blocking of the openings on pit membranes by movable extractives when water flows through the cell lumen. Storing western hemlock wetwood in water at room temperature reduces its water permeability. Wet pockets that form when wetwood of western hemlock is subjected to kiln-drying have lower permeability than the dried portion of the lumber.


Erickson, H. D. 1960. The effects of storage conditions and time upon permeability of green sapwood. Proc. Am. Wood Preserv. Assoc. 56:156-165.nKelso, W. C., R. O. Gertjejansen and R. L. Hossfeld. 1963. The effect of air blockage upon the permeability of wood to liquids. Univ. Minn., Agric. Exp. Sta., Tech. Bull. 242.nKozlik, C. J., and L. W. Hamlin. 1972. Reducing variability in final moisture content of kiln-dried western hemlock lumber. For. Prod. J. 22(7):24-31.nLin, R. T., E. P. Lancaster, and R. L. Krahmer. 1973. Longitudinal water permeability of western hemlock. I. Steady-state permeability. Wood Fiber 4(4):278-289.nLin, R. T., and C. J. Kozlik. 1971. Permeability and drying behavior of western hemlock heartwood. Proc. West. Dry Kiln Club, 22nd Annual Meeting, Portland, Oregon.n






Research Contributions