Methods of moisture measurement in historical masonry with examples of use on archaeological sites under the 3rd courtyard of Prague Castle
Abstract
The degradation of masonry of historically valuable structures is often linked to the presence of moisture which then affects saline, frost, and biogenic weathering or swelling of clay minerals. The article presents the use of selected methods for monitoring the presence of water in heritage properties, with emphasis on the use of these methods in conservation, summarizing their principles, advantages, disadvantages, and the possibilities of combining them.
The selected methods (resistive, electromagnetic, infrared, probe using reactive dye) are presented and critically evaluated using a case study of moisture monitoring in the archaeological area under the third courtyard of Prague Castle. The microwave method with a greater depth range is recommended as the most suitable non-destructive method - on the contrary, electromagnetic probes with a lower depth of measurement are significantly distorted by the shape of the surface of the measured material and cannot be recommended.
Resistivity methods are prone to error in saline materials, but are an adequate choice when funds are limited. Moisture content in the surveyed gaize (opuka) pillar of the early modern bridge below the Third Courtyard appears to be stagnant at present, but the measured time series are too short to draw responsible conclusions, and measurements are continuing.