## 4 IRT Different Case Studies from Diagnosis to Protection Interventions
### Assessment of Conservation Interventions
#### 4.3.2 Consolidation Interventions  
The application of a consolidation material aims to restore the cohesion of a weathered stone. A consolidant should fulfil specific requirements that deal with the change in the porous structure of the stone, the impact in moisture transfer and compatibility with the authentic structure. Stone consolidation is quite a risky conservation intervention. Nonetheless, it is a necessary intervention since stones decay and loose cohesion in the exposed surfaces down to a certain depth. Many consolidation materials form a film on the surface of the stone that obstructs the conventional transport of water-moisture via the capillary systems within the stone(s). However, the evaporation of water should usually also be considered, especially in cases where intense environmental conditions are present (i.e., high winds, elevated temperatures) as these accelerates the evaporation rate, leading to the formation of salt efflorescence and crystallisation and, thus, accelerated damage for the structure. A consolidant must be hydrophilic allowing the water to pass through the treated layer of the stone. It must also have the ability to penetrate the stone (i.e., low viscosity), and it should not present or cause any colour alterations to the stone. There are various application techniques for stone consolidation. Commonly, they are applied to the surface of the stone by brush, spray, pipette, or by immersion, and are drawn into the stone by capillarity. In this work, IRT (AVIO TVS-2000 Mk II LW, 8-12 \(\upmu\)m) was used in the investigation of consolidated porous stone structures. It has been shown that, due to the difference between the thermal diffusivities of consolidated and untreated stones, thermography is capable of imaging large areas and displaying qualitative dissimilarities in penetration depth these emerge as surface temperature variations on the obtained thermal images. It has also been shown that simulating work in the laboratory can be important in order to interpret the results properly as far as a consolidation treatment is concerned. The masonry is orientated in a south-easterly direction. The materials used were silicon-based materials since they present good compatibility with the stone and chemical stability owing to the Si-O-Si bond, preventing discolouration. Furthermore, due to the low viscosity of these products, they provide deep penetration in the stone. The capillary system of the stone in combination with the low viscosity of the solutions used, facilitated the application of spraying; the products are presented in Table 2. \begin{table}
\begin{tabular}{c c} \hline \hline
**Symbol** & **Description** \\ \hline RP & Ethyl silicate \\ EU & Acryl silicone resin \\ PH & Prehydrolysed ethyl silicate with amorphous silica \\ PL & Aqueous colloidal dispersion of silica particles \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Description of consolidants. Figure 13: Dome of Katholiko in Holy Selphuchre Temple, area of investigation and corresponded thermogram. Thermal images were acquired 3, 15, 28 and 33 months after the consolidation treatment. Below a representative result from a thermographic survey from the investigated masonry (Figure 14) 3 months after the consolidation treatment (Figure 15) is presented. Different temperatures at the same height of the stonework were noticed, due to the use of the various consolidants (air temperature 13 \({}^{\circ}\)C, relative humidity \(\sim\)65%). Although the images were acquired at different times/seasons, it can be said that treatments with RP and EU present relatively higher temperatures when compared to the treatments with PH and PL. This is probably due to the fact that the first two treatments amend the respiration of the stones. It can thus be concluded that the different temperatures among the consolidated areas of the examined masonry are due to the physico-chemical variations that the consolidants present in comparison to the authentic stone.