## 3 Results and Discussion
### XPS Data Matrix
Subsequently, the percentage inversion of carbonates and Al-silicates was already predictable in the graphic trend, fully achieved after 52 months of sampling, clearly represented by a progressive decrease in calcium and carbonate carbon and by a strong increase in silicates and aliphatic/aromatic and functionalized carbons. Figure 6: Compositional changes of calcarenite walls versus exposition time outdoors for the new building (periodic sampling up to 52 months) in reference to the old farm. The decay trend completes that in S2b by adding the intensity variation in percentage of the chemical groups (listed in the legend) averaged over four samples, at each sampling time, beyond nine months. Overall, it starts from the reference calcarenite (0 exposition time) and is projected towards an extremely long time represented by samples1v–4v taken from the old farm, reported as ‘averaged’ in the rightmost part of the graph. Interestingly, in the absence of intermediate sampling, it can be inferred that the exposure time prolonged over two years leads, at some stage, to a sort of stabilization of the degraded calcarenite, at least regarding the similarity of the surface composition for both buildings, as evident in the last part of the graph in Figure 6. Indeed, the'same' component groups, of nearly the'same' percentage distribution, within the indicated error bar characterize the averaged samples collected from the new building (52 months of sampling) and old (1v-4v sampling) farmhouse. The trend shown in Figure 6 highlights the decay phenomena that can be justified by the continuous dissociation and dissolution of the carbonate matrix and by the concomitant increase in aliphatic/aromatic carbons due to the deposition of incombustible carbon particles and of functionalized carbons probably accentuated by the presence of lichens and algae, as shown in the SEM (Scanning Electron Microscopy) images acquired on the samples collected after 12 months of exposure from the cube walls [13; 14]. Some images with included EDS microanalysis are reproduced in Supplementary Figure S3, together with the list of identified bacteria of the genus _Bacillus_, available from the (unpublished) PhD thesis. The presence of lichens in the subsurface zones supports the hypothesis according to which the calcarenite rocks, in addition to the evident degradation of their carbonate matrix due to atmospheric agents and acidity of rainwater, undergo an increase in porosity augmented by freeze-thaw cycles [8; 9; 29]. As experimentally verified with timed tests on the capillarity of calcarenite stones ([13; 14] and PhD report), the expansion caused by the internal pressure exerted by frozen water promotes biocolonization. The colonizing microorganisms that tend to settle inside the pores and interstices of the stone material induce the reduction of the interstitial porosity, as shown in Figure S3. The evolving stages of colonization were testified by the biological analysis anticipated in the Introduction, carried out on samples taken from the walls of the cubic building at the end of two years of exposure and, for comparison, also from the walls of the farmhouse. The same microorganisms were found, using the analytical techniques mentioned above for both buildings, and similarly distributed on the surfaces (bacteria belonging to the Bacillus family, listed in Figure S3) and beneath surfaces (lichens/ fungi listed in ref. [14]) on inner faces more protected from environmental threats together with mono- and di-hydrated calcium oxalates detected by XRD (PhD report), derived from the dissolution of carbonates by oxalic acid, one of the bio-metabolic products. The degradation trend of calcarenite outlined in Figure 6 fully accounts for the bioactivities of the'same' colonizers in determining the surface composition of the new building walls to evolve towards that of the old building walls, left exposed to the outside in similar conditions for over a century.