## 3 Materials Used for Restoration and Conservation of Masonry Elements
### Biocidal Interventions  
#### 3.2.1 Classical Approaches  
The biodeterioration of masonry materials can be divided into three main categories, considering the microorganisms involved: deterioration caused by bacteria, by fungi or by lichen [53]. Table 3 presents some examples of biodeterioration induced by different organisms in masonry materials.  
The literature is much more focused on the identification of the microorganisms affecting the masonry materials than the proposal of new alternative treatments. As there are no substances particularly developed for cultural heritage, the biocidal substances used were typically those developed for other applications (such as commercially available pesticides, based on active ingredients as glyphosate, benzalkonium chloride, \(N\)-octyl-isothiazolinone, usnic acid, etc.) [61] or natural materials, such as natural extracts and essential oils [62; 63] or lipopeptides [64].  
Another potential approach is represented by the physical decontamination methods (such as the mechanical cleaning, the use of ionizing or UV-radiation) [65]. These latter methods possess a series of disadvantages (the mechanical cleaning could damage the substrata, UV and gamma radiation can induce color changes). However, with the identification of the potential hazard to human health and to the environment of those methods, the need for dedicated pesticides became evident. Among the first solutions proposed were the natural alternatives (plant extracts, essential oils, etc.), their use being recently reviewed by [PERSON] and [PERSON] [66]; although the approach has some advantages (such as  
\begin{table}
\begin{tabular}{p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt}} \hline \hline
**Support** & **Site** & **Biodeteriogens** & **Effect** & **Ref.** \\ \hline Adobe & Capayán ruins (Argentina) & _Centris muralis_ Burmeister bee & Massive erosion, high density of cavities & [54] \\ \hline Limestone and lime stucco & Maya constructions (Mexico) & Fungi, cyanobacteria & Dissolution and recrystallization of calcite, physical breakdown & [55] \\ \hline Limestone and lime mortar & San Roque church, (Mexico) & Cyanobacteria and Bryophyta & Apparition of dark green to black biofilms after restoration & [56] \\ \hline Sandstone & La Galea Fortress (Spain) & _Trentepollui_ algae & Reddish biofilm, material disintegration, erosion, discoloration & [57] \\ \hline Limestone & Chalais Abbey (France) & Alphaproteobacteria, Actinobacteria, Cyanobacteria, Bacteroidetes, Bacteroidetes, Betaproteobacteria, Betaproteobacteria, Deinococcus, Acidobacteria, etc. & Biocorrosion, discoloration, detachment of mineral grains, salt crystallization & [58] \\ \hline Mortar & Casa Godoy (Porto Alegre, Brazil) & Casho Gordy (Porto Sheparemire, Cladosporium sp.; _Leanctillium_  
the good efficiency, or a potential eco-friendly character), in our opinion, the lack of supplementary data, regarding the interaction with the material itself, as well as regarding the behavior over longer period of times, makes the solution of natural biocides inapplicable at this time in the field of cultural heritage.