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Warehouses are big architectonical structures mostly made of spruce wood and utilized as storage buildings principally by food traders in Northern Countries. Trondheim’s warehouses currently observable along the river Nidelva, date back between the 17th and half of the 19th century were mostly used to stock and process fish. Therefore, where the food goods were stored, residuals are expected to be still present and/or to be responsible for the formation of alteration products on the wooden surfaces as well as inside the wooden structure. Here we propose a characterization of residual and neo-formed compounds inside and on the surface of wooden logs by means of vacuum microbalance that allowed both to individuate the type of salts, as well as, to estimate the maximum water film thickness adsorbed on the wooden samples at 93% of RH. These data have been related to variations in the acoustic emission (AE) intensity detected at the log surface and to the wood moisture content measured with capacitive and resistance operating moisture meters. The application of three independent techniques have allowed obtaining interestingly information indicating their potentiality as decay assessment techniques in the field of historical materials and specifically in the study of salts weathering on wood. The methodology allowed identifying a clear relationship between the amount of water in logs as a function of their distance from the ground and variations in the amplitude of the acoustic emission signals.

Acoustic emission is a well-known noninvasive methodology for the study of defects in materials but still rarely applied in the field of cultural heritage diagnostic. How alteration products and degradation processes affect the acoustic emission signal still is an open issue. The proposed study concerns the utilization of such techniques to investigate the relations existing between the moisture content and the typology and amount of crystallized salts with the acoustic emission features. This work focuses on spruce wood logs belonging to an historical warehouse in Trondheim, Norway, since no strictly scientific studies exist on the conservation conditions of these big wooden structures. The methodology, also involving the moisture content measurement of structures and the samplings of portions analyzed through vacuum microbalance, allowed identifying a clear relationship between the amount of water in logs as a function of their distance from the ground and variations in the amplitude of the acoustic emission signals.