Exposing drying patterns: using electrical resistivity tomography to monitor capillary rise in sandstone under varying drying conditions

Rising damp and other moisture movements through porous stone and rock are known to cause weathering and deterioration, as noted in a range of recent field and laboratory studies. However, relatively little is known about the behaviour of moisture within a porous stone under realistic conditions because of lack of suitable monitoring methods. This paper has two main aims: firstly, to evaluate different electrical (resistivity and capacitance) methods to monitor subsurface and surface moisture regimes and, secondly, to use these methods to monitor the movement of water by capillary rise in a sandstone block under (a) conditions of constant moisture ingress at the base and (b) an enhanced drying regime with and without constant moisture ingress at the base. Our results indicate that, for electrical resistance tomography (ERT) measurements on a sandstone block, medical electrodes provide more reliable contact with the stone than spring-loaded pointed metal electrodes, and that the combination of ERT and handheld moisture meters gives a realistic picture of moisture movements within the block. The capillary rise and drying experiments reveal complex moisture movement over time and space. Under conditions of constant moisture supply, accelerated drying results in maintained or enhanced capillary rise. These findings are presented to further our understanding of the behaviour of moisture within porous sandstone.