**4. Conclusions**

Lime mortars prepared with the addition of organic additives have been used for centuries in building constructions and, more recently, for restoring and protecting historical buildings. In Mexico, the use of *Opuntia ficus-indica* mucilage in mortars is a traditional procedure, but despite the large use, only in recent years, a scientific approach was used to evaluate the effectiveness of this practice and to elucidate the physicochemical mechanisms involved. In our work, we demonstrated the formation of a more regular crystalline structure in bio-mortars containing succulent plant extracts in respect to mortars prepared without vegetable extracts or with *Salvia hispanica* mucilage. The biochemical analysis showed the different composition of mucilage of Cacti species versus *Salvia hispanica*, confirming the role of the gelling species in the mortar structure formation. Furthermore, the radiographic tests confirmed a similar performance between *Opuntia ficus-indica* mucilage and Primal acrylic resin when added at the same percentage to the lime mortars, indicating that a green product could efficiently substitute a synthetic component. Moreover, the bioreceptivity studies indicated that, although the role of the different mucilages can be similar in enhancing the durability of the bio-mortars, they are not suitable as additives in the same way: while the *Aloe vera* mucilage gives the bio-mortar a high susceptibility to biological attacks, the bio-mortars added with *Opuntia ficus-indica* and *Opuntia engelmannii* mucilage show a very low bioreceptivity, probably due to the presence of a higher content of hydro-soluble phytomolecules such as polyphenols, thus making the *Opuntia* mucilage a good candidate as a sustainable alternative to chemical additives. More detailed biochemical composition studies will help to elucidate the role of the different components of the vegetable mucilage additives, paving the way for their widespread uses in restoration as a modifier and/or consolidant.

**Author Contributions:** Conceptualization, C.A., L.B. and F.P.; Data curation, E.B., S.P. and A.T.; Formal analysis, L.B. and E.B.; Funding acquisition, C.A. and F.P.; Investigation, A.R.S. and S.P.; Methodology, M.F., M.I. and M.F.F.M.; Project administration, C.A., L.B. and F.P.; Resources, C.A., L.B. and A.M.O.; Software, A.T.; Supervision, C.A., L.B., M.I. and F.P.; Validation, C.A. and A.M.O.; Visualization, C.A. and L.B.; Writing—original draft, C.A. and M.I.; Writing—review & editing, C.A., L.B. and S.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** The research was funded by a gran<sup>t</sup> fromthe Italian Ministry of Foreign Affairs and International Cooperation (Progetto Grande Rilevanza PGR01082).

**Institutional Review Board Statement:** Not applicable

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data sharing not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
