## 4 Results and Discussion  
### Mortar Characterization  
The selected mortar and plaster samples were analyzed using X-ray diffractometry to determine the bulk mineral composition (Table 2 and Figures S1-S5 in the Supplementary Materials). Carbonate phases such as calcite (ranging from 9 to 70%), aragonite (0.9% in sample MV_SS_01), and magnesite (abundant in samples MV_SS_02 and MV_SS_10, accounting for 11% and 17%, respectively) were identified, along with silicate phases including quartz, micas, feldspars (albite), and magnesium-rich clay minerals. Quartz, feldspars, and mica could be associated with the inert fraction of the aggregate, while calcite and magnesite may be due to both the carbonate binder fraction and the presence of carbonate sand in the aggregate. The presence of magnesium-rich phyllosilicate clay components (chlorite and montmorillonite) suggests an intentional or accidental addition to the mortar mix. The mineral composition also revealed the presence of hydotalcite-like phases (magnesium hydroxy-aluminates, LDHs), ranging from 0.1% to 3.8%, associated with abundant fractions of amorphous phases (up to 30%), indicating partial hydraulic reaction processes. Reactive silicate components likely reacted to form complex paracrystalline products such as hydrated calcium and magnesium silicates and aluminates, as well as LDHs due to hydraulic reactions. These reaction products can trap carbon dioxide, introducing younger carbon into the system, thus compromising radiocarbon analyses, causing the dating to be closer to the present time. Sample MV_SS_02 is indicative of the white finishing surface layer, characterized by high contents of calcite and magnesite and small fractions of silicate aggregate, which is consistent with the mineral composition of an internal lime-plaster layer. Sample MV_SS_10 exhibits high content levels of magnesite, calcite and hydromagnesite, in addition to amorphous phases, which is indicative of a magnesian lime plaster with reaction phases (LDH) resulting from partial hydraulic reactions. The presence of magnesite and/or hydromagnesite is indicative of the use of a magnesian-type binder characterized by good binding capacity and mechanical strength. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Samples** & **Calcite** & **Aragonite** & **Magnesite** & **Quartz** & **Albite** & **Micas** & **Mg-Clay** & **HydroMg** & **LDH** & **Amorp.** \\ \hline MV\_SS\_01 & 21.0 & 0.9 & 0.4 & 20.2 & 5.8 & 12.9 & 6.7 & 0.0 & 3.8 & 28.2 \\ \hline MV\_SS\_02 & 70.2 & 0.0 & 11.0 & 4.2 & 1.6 & 4.1 & 0.9 & 0.0 & 1.8 & 6.3 \\ \hline MV\_SS\_07 & 9.1 & 0.0 & 1.7 & 27.9 & 7.3 & 15.3 & 6.4 & 0.0 & 2.8 & 29.2 \\ \hline MV\_SS\_08 & 22.8 & 0.0 & 0.0 & 27.8 & 7.6 & 7.4 & 1.7 & 16.9 & 0.1 & 15.8 \\ \hline MV\_SS\_10 & 29.7 & 0.0 & 17.5 & 0.1 & 0.0 & 1.7 & 0.0 & 19.5 & 1.0 & 30.5 \\ \hline \hline \end{tabular}
\begin{tabular}{c c c c c c c c c} \hline \hline \multicolumn{1}{c}{Mg-Clay: magnesium clays; HydroMg: hydromagnesite; LDH: layer double hydroxide, as hydotalcite and hydrocalumite phases; Amorp.: amorphous content.} \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Quantitative XRPD analysis, expressed as %wt of the mineral phases identified in the analyzed samples. From a mineral-petrographic perspective, optical microscopy investigations (Figure 4) revealed that samples MV_SS_01, MV_SS_07, and MV_SS_08 are mortars with binder/aggregate ratios of 1:1. The binder matrix exhibits a micritic texture with high interference colors typical of calcite and zones of darker coloration which can be attributed to low-crystallinity phases. The inert fraction primarily consists of quartzites, feldspars, and mica, with angular clasts characteristic of a fluvial aggregate with minimal erosion. In samples MV_SS_01 and MV_SS_07, the inert fraction appears poorly selected, with grain sizes up to 10 mm in length distributed non-uniformly and non-oriented within the mix, while in sample MV_SS_08, the aggregates are moderately selected and more uniformly distributed.