## 4 IRT Different Case Studies from Diagnosis to Protection Interventions
### Assessment of Conservation Interventions
#### 4.3.3 Cleaning Interventions of Architectural Surfaces  
The cleaning of stone and architectural surfaces results in aesthetic and physicochemical alterations to the applied surface. According to the British Standard 8221-1:2000 [27], buildings are cleaned either to enhance their appearance (i.e., removal of disfigurements, reveal the natural colour/details of building, restoration of building appearance that has been altered/repaired) or to assist maintenance and/or conservation (i.e., removal of harmful substances in order to arrest decay, exposure of concealed defects to establish the extent and nature of necessary repairs, preparation of surface for additional treatments, fulfilment of the terms of a lease that requires periodic cleaning of a building).  
Figure 14: Consolidated masonry under investigation.  
Figure 15: Thermogram of investigated-consolidated masonry.  
There are various cleaning techniques, ranging from those that are intended for use on large facades to those that are intended for meticulous use on finely carved and delicate sculpture. Their efficiency is commonly assessed subjectively. IRT can be employed in order to assess any surface alterations (i.e., roughness) after a cleaning application [28], as well as to investigate any moisture deposits in the examined surfaces.  
In this case, IRT (AVIO TVS-2000 Mk II LW, 8-12 \(\upmu\)m), was used with the intention of investigating the efficiency of specific cleaning treatments on certain architectural surfaces of different materials and decay patterns at the historic Bank of Greece building in Athens. The cleaning methods applied on the architectural surfaces were either distilled water with controlled pressure or sepiolite poutlices. In Figure 16, we present: a white Pentelic marble surface (left), a metamorphic limestone consisting almost exclusively of calcite grains and quarried from mountain Penteli in Athens and the investigated porous stone surface ([PERSON]'s stone), consisting mainly of calcite minerals and quarried from the Kapandriti area in Attica (right).  
From the acquired thermograms (Figures 17 and 18), different temperatures can be observed on the surfaces according to the applied cleaning method. The air temperature was about 16 \({}^{\circ}\)C and air relative humidity was 55%. Sepiolite residues were traced on the cleaned architectural surfaces by poutlices (left side of thermograms), leading to a withholding of moisture and therefore lower temperatures on the thermograms compared to the cleaned areas on the right (i.e., distilled water with controlled pressure). A thorough water rinse should take place whenever sepiolite poutlices are applied for cleaning, while the use of Japanese paper between the poutlice and the material to be cleaned is also recommended. Furthermore, the sepiolite poutlices should be covered with polyethylene film so as to prevent swift water vaporization when at high temperature and low humidity conditions that leads to the hardening of the sepiolite on the stone.  
Figure 16: White Pentelic marble surface (**left**) and [PERSON]’s stone surface (**right**) at the historic Bank of Greece building in Athens.  
Figure 17: Thermal image of White Pentelic marble surface.