## 4 Conclusions  
This study has provided a comprehensive analysis of the factors contributing to the deterioration of natural stone in the rupestrian church in Jac, Romania, focusing on the combined effects of microclimatic conditions and microbial activity. The findings underscore the multifaceted nature of stone degradation, influenced by physical, chemical, and biological processes. The physical disaggregation of stone is significantly influenced by  
Figure 12: Processed SEM images of the samples of sandstone from the rupestrian church. The green color suggests the presence of identified fungal hyphae and spores on and within the matrix of the kaolinite–illite assemblage (blue) (**a–f**)–different SEM images of the analyzed samples). environmental conditions such as T fluctuations and RH variations. The freeze-thaw cycles, common in the Romanian climate, cause expansion and contraction within the stone's pore structure, leading to mechanical stress and eventual cracking. The data collected over 12 weeks demonstrated substantial T and RH variations within the church, contributing to this type of weathering. Chemical weathering is another critical factor affecting the integrity of the stone. The solubilization of minerals by organic and inorganic acids, as observed in the sandstone samples, plays a significant role in the chemical breakdown of the stone. RS and XRD analyses confirmed the presence of quartz, muscovite, and feldspars, which are susceptible to dissolution under acidic conditions. The high levels of VOCs detected within the church further exacerbate this chemical weathering process. Through oxidation and other chemical reactions, VOCs can produce acids that accelerate the deterioration of the stone's mineral composition. The biological aspect of stone deterioration was a central focus of this study. The culture-based identification methods revealed the presence of several fungi, including _Cladosporium herbarium_, _Aspergillus niger_, and _Morierella hyalina_. These fungi contribute to biodeterioration through biocorrosion and biomineralization processes. SEM images provided visual evidence of fungal hyphae and spores infiltrating the kaolinite-illite matrix, demonstrating the extent of microbial colonization. The metabolic activities of these microorganisms lead to the production of organic acids and enzymes that further degrade the stone's structure. This study also identified that high church RH levels create an ideal microbial growth environment. With RH averaging 90.6% and often exceeding 99%, the conditions are highly conducive to fungal proliferation. This excessive moisture supports microbial activity and facilitates the dissolution and transport of salts within the stone, leading to efflorescence and further structural weakening. The comprehensive microclimatic data highlight the interplay between environmental conditions and stone decay. High levels of PM\({}_{2.5}\) and PM\({}_{10}\) were observed, which not only have abrasive effects on the stone surfaces but also act as carriers for microbial spores, thus enhancing biological contamination. Given the multifaceted nature of stone deterioration identified in this study, it is clear that effective preservation strategies must be equally comprehensive. Stabilizing the microclimate within the church is paramount. Additionally, monitoring and reducing indoor pollutants, particularly VOCs and PM, are crucial to preserving the stone's integrity. Biocontrol measures are also essential to mitigate the impact of microbial colonization. Regular cleaning and applying biocides can help control the growth of biodeteriogenic fungi. Furthermore, protective coatings that are permeable to water vapor but resistant to microbial penetration could be applied to the stone surfaces to provide an additional layer of defense (different nanoparticles, siloxane-based coatings, acrylic polymer coatings, silicate-based coatings, alkylalkoxysilanes, etc.). Conceptualization, D.C.I. and A.-I.A. ; methodology, A.-I.A., C.M., T.C. and L.B.-T.; software, T.H.H. and L.-C.N.