## 1 Introduction  
The protection of ancient stone monuments and objects is one of the topics of the recent research in the field of conservation of cultural heritage [1]. Stone materials are affected by degradation processes such as black crusts, efflorescents, decoesions, etc., caused by several chemical, physical, and biological factors. Among others, water is one of the main causes of degradation, playing an important role in many decay mechanisms [2]. It acts in a direct way through a solubilization action and in an indirect way through freeze/thaw cycles, pollutant transport, and soluble salt hydration. In addition, water may promote the growth of biological organisms which may cause material degradation. It is well known that hydrophobic treatment is one of the most important interventions usually carried out in the conservation of stone artefacts and monuments, preserving them against the water [3, 4]. The choice of hydrophobic products should be aimed at preventingliquid water penetration, to allow vapour leakage, delaying degradation processes, and to avoid chromatic alterations, leaving open at the same time the stone porosity for water vapour flow [5; 6]. Nowadays, the use of hydrophobic polymers is generally accepted as being suitable due to their protective action, even if the direction of the research is also aimed at the development of innovative and inorganic materials [7]. The evaluation of protection actions is based on the regulations by the European Committee for Standardization (CEN TC 346) [8; 9]. Calcarenites are used in the most important testimony of ancient and modern monuments of Sicilian history. The different lithotypes, possessing different porosity and mineralogical features [10], are present both in the east (Noto \"white type\" and Comiso) and in the west (Palermo, Mazara, Agrigento, Cusa). Indeed, the performance of a polymeric protective can be different for different lithotypes, as demonstrated in our previous papers [11; 12]. In most cases, the choice of the best protective is made based on a compromise between several factors, such as hydrophobicity and aesthetic appearance [13]. The reason for the different behaviour of different protective concerning one specific lithotype could be seen in the different microscopic interactions that occur, which could also be connected with the macroscopic behaviour [14]. The interactions between the two materials (stone and polymer) can be responsible for the variations in the structural organization of the polymers when they are in contact with the stone surface, and these can depend not only on chemical factors but also on physical factors related to the porosity and dimensional distribution of pores [15]. For this reason, the goal of this work is to verify the connections between the macroscale properties and the microscale properties of protected stone material. The work is carried out on Cusa's stone, a calcarenite coming from the ancient and renowned quarries of Cusa near the acropolis of Selinunte (TP), used for the construction of most of the temples in the archaeological park of Selinunte, the largest in Europe [16], in particular, Temple G, which is one of the most impressive temples of Magna Grecia. In our previous paper, the effectiveness of the protective treatment of three formulations (the polysiloxane Wacker 290 and two fluorinated elastomers, Fluoline HY and Fluo AQ of CTS s.r.l.) was investigated using water absorption by capillarity, water vapour permeability and colorimetric tests [12]. The obtained results show that all three formulations conferred protective properties, but Fluo AQ is the protective agent giving the best performance. The Fluo AQ guarantees a permeability similar to that of natural stone and drastically reduces the water absorption, thus giving it high water repellence. Conversely, the Fluoline HY significantly reduces the water vapour permeability of the stone and shows little water repellence.