Evaluating the biosusceptibility of natural stone as an supporting tool to prevent Cultural Heritage biodeterioration

Biodeterioration of construction materials is still a major challenge that conservator-restorers face, especially in historic monuments with high cultural value. Natural stone is highly susceptible to deterioration through physical, chemical, and biological ways, whereas biological proliferation may potentiate both chemical and physical deterioration. The composition of the colonizers and their proliferation are highly dependent on climatic parameters like temperature and humidity, which are distinct from place to place. The present work proposes the execution of an innovative methodology that enables the determination of the susceptibility of natural stone to biocolonization, a parameter denominated as biosusceptibility. The study aims to contribute to the creation of models by predicting their deterioration even before the objects’ manufacture, promoting the sustainability of one of the most valuable natural resources. The methodology proposed here was performed on limestones, marbles and slates—exploited in the Portuguese territory—by using colonizing strains typically found on stones exposed to the Mediterranean climate. The results have demonstrated that the stones with higher porosity are less susceptible to epilithic colonization and, consequently, with a moderate alteration of their aesthetic appearance. However, the metabolic activity determined in these stones is higher, which indicates that biocolonization will cause more severe damage to their structure in the future. The first significant changes on the stones’ matrix were assessed one year after the inoculation, using cutting-edge technology of 3D surface micro-reconstruction. Due to its relevance in natural stone deterioration processes, the inclusion of the biosusceptibility information in technical brochures is strongly encouraged. Graphical Abstract