Evaluating dimensional stability in solid wood: a review of current practice

The degree with which wood shrinks and swells with changing moisture content is an important property which determines its suitability for different applications. This property, known as dimensional stability, is often a target property for improvement in wood modification research. Its importance makes it a commonly quantified wood property. Despite this, methods for measuring dimensional stability are not standardised, and there is little consensus on appropriate test methods. Dimensional stability tests can be classified according to the method used to change the moisture content of the wood (liquid water or water vapour) and the duration of the test (until equilibrium is reached, or a shorter duration). Each class of test represents a situation that wood products may encounter in service, and different types of wood (modified or otherwise) may respond differently to each situation. This means that comparative performance between different wood types may be dependent on the test used (and may not be valid for some situations encountered in service). In this paper, standard test methods and methods described in the literature are compared, and recommendations are given for selecting an appropriate dimensional stability test and for minimising sources of bias and measurement uncertainty in the test. It is expected that this will also encourage the adoption of more standardised test methods, enabling comparisons to be made between different studies and different wood types.