Environmental Controls on Stone Erosion Rates in Monuments Affected by Salt Crystallization

Abstract

This study focuses on quantifying the erosion rate of building stones from Jamete's Arch in the Cathedral of Santa María in Cuenca, considered one of the most iconic works of the Spanish Renaissance. This monument exhibits severe deterioration due to salt crystallization, a common and highly aggressive process affecting architectural heritage worldwide. The intensity of erosion is largely influenced by the environmental exposure conditions of the cathedral´s interior microclimate. The innovative methodology proposed in this research combines various elements, which include: a comprehensive characterization of the efflorescence, along with the petrological and petrophysical properties of the stone; continuous monitoring over one year of the environmental exposure (temperature and relative humidity) and direct measurement of the erosion rate experienced by the monument's stones. The results reveal that the critical deterioration of the stones is primarily driven by phase transitions of magnesium sulfate, which crystallizes within the stones’ porous system. The highest erosion rates are concentrated at the end of summer and throughout autumn, coinciding with the greatest number of phase transitions between epsomite, hexahydrite, and kieserite. These phase changes generate crystallization pressures that exceed the mechanical strength of the stone. The methodology employed in this study suggests the implementation of a controlled system for the preventive conservation of the monument. This system focusses on environmental control with temperature and relative humidity monitoring to regulate interior microclimate conditions and reduce/eliminate the cycles of salt dissolution and crystallization. Such a system would minimize stone deterioration and significantly reduce the need for costly restoration interventions. © The Author(s), under exclusive licence to ProGEO - International Association for the Conservation of Geological Heritage 2025.