Material moisture content of wood and cement mortars – Electrical resistance-based measurements in the high ohmic range

Abstract

The performance of porous and hygroscopic building materials is closely connected to its sorption properties and ability to get wet. Weight, mechanical, acoustic, and thermal properties as well as the resistance to discoloring and decay causing organisms are affected by moisture. For various reasons and purposes it is therefore recommendable to monitor the moisture content of building components continuously. The most common and most easily applicable methods are electrical resistance measurements. They can be applied to wood and wood-based materials as well as to mineral products such as mortar and brick. However, resistivity measurements require material specific characteristics and a temperature compensation since both parameters have a significant effect on electrical conductivity.This study aimed on developing a model to determine the moisture content at any temperature for different building materials such as native and modified wood as well as untreated and hydrophobized mortar. Therefore, the electrical resistance was measured with a data logging device in the giga ohm range to obtain values at low moisture contents. The model enables measurements at a wide range of moisture contents and suited with an acceptably high accuracy by using the appropriate resistance characteristic for each building material.