Monitoring of the temperature–moisture regime in St. Martin’s Cathedral tower in Bratislava

Buildings are often composed of materials with a porous structure. Moisture in the masonry has a destructive impact caused by cycles of drying–wetting and freezing–thawing. A new sensor principle for monitoring moisture in the masonry is presented herein. This sensor utilizes changes in the thermal conductivity of porous structures when they are filled with moist air, water, or ice depending on the existing thermodynamic conditions. Herein, the “hot-ball” method is used to measure the thermal conductivity. The moisture sensor is prepared for porous material corresponding to the parent material, whether it is rock, brick, or concrete. This parent sample is taken from a borehole drilled into the wall. Methodology for moisture sensor calibration is also presented. Sensors were placed in the masonry walls of St. Martin’s Cathedral tower in the North, South, and West orientations. The sensors were placed in the plaster and bricks at depths up to 60 mm in the wall surface, just below the window sill. The temperature–moisture regime was monitored from August 19th, 2011 to March 30th, 2012. Changes in temperature and moisture were then correlated with meteorological data.