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Measurement and practical application of tangential dimensional change coefficients to hardwood flooring




Publication type:

Research Paper (RP)

Primary Station(s):

Forest Products Laboratory


FS Research Paper


Dimensional movement with changing moisture content is among the main performance characteristics of wood flooring. The U.S. wood flooring industry has relied on values and equations published by the Forest Products Laboratory (FPL) in its Wood Handbook to provide critical information about how different woods move. This paper discusses key information previously published by FPL relating to dimensional change coefficients (DCCs) and includes laboratory measurements of board width over a range of moisture contents for four types of prefinished commercial solid wood flooring: hickory, red oak, Acacia cf. confusa, and Acacia cf. mangium. Floorboards were initially conditioned to equilibrium at 80% relative humidity (RH), remanufactured to new target widths, and installed on subflooring assemblies according to industry guidelines. The assemblies were subsequently equilibrated at 30% RH and then again at 80% RH. Time-lapse videos are provided for each wood type, showing shrinkage and swelling with changing moisture content (MC) at two image magnifications. DCCs for installed floorboards were calculated based on measured widths and MCs at the two conditions. In addition, DCCs for uninstalled floorboards of the woods in this study were experimentally determined across a range of moisture conditions using two different calculation methods. Comparison of experimentally determined DCCs for uninstalled and installed floorboards indicates that there is no practical installation constraint on shrinkage of installed floorboards. No practical difference in DCC was found between tongue-and-groove floorboards and matched boards cut to a rectangular profile. Experimentally determined DCCs for hickory and red oak are within a reasonable range of Wood Handbook values, and we report the first published DCC values for the two Acacia. Reporting DCCs to two significant figures (rather than three) is recommended given the variability underlying the DCCs in the Wood Handbook and the variability in DCCs experimentally observed in this work. Practical methods for determining DCCs are discussed for species lacking published data. Incorporating variability in width measurement, MC, and DCC value in the calculation of moisture content at the time of manufacture results in a range of initial MCs that spans the actual MC, whereas using single, average values does not accurately predict the initial MC in three of four cases


Glass, Samuel V.; Boardman, C.R.; Ravindran, Prabu; Wiedenhoeft, Alex C. 2022. Measurement and practical application of tangential dimensional change coefficients to hardwood flooring. Research Paper FPL-RP-711. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 22 p.


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