Trä och fukt – Mätmetoder för fuktrelaterade dimensionsförändringar hos trä och deras användbarhet, med två fallstudier inom konservering

Abstract

This thesis deals with different methods for measuring moisture-related dimensional changes of wood. Typically relative humidity is measured to determine if the ambient climate around an object is harmful to it or not. Values between 40 to 65% RH are recommended for hygroscopic materials. To know how a wooden object actually reacts to changes in the surrounding environment requires methods that involve the object itself. Because of the wood anisotropy, differences in wood structure, finishes and other restraints, it is not always possible to predict the movements. This paper addresses various measurement methods, primarily methods that have been tested in the field of conservation, with examples of their use. Topics that are discussed are how the methods work, what information they provide and their pros and cons. Two case studies provide detailed examples of some methods, first, the use of electric linear meters in the ceiling of Vänersborg church and second, weighing and shrinkage measurement with callipers on the warship Vasa. The purpose was not to find the ultimate measurement method, it doesn´t exist, but to explore different methods and their applications. All methods must be combined with measurements of RH and temperature to create a connection between cause and effect. Different methods give answers to different questions and may need to be combined with each other. When selecting the method of measurement, one must also question the usefulness of the information in relation to any damage to the object.