## 4 Materials and Methods
### Experimental Methodology  
The procedure employed in the SDI method involved several basic phases. Firstly, before each operation, it was necessary to prepare the tested surface to ensure the perfect penetration of the ready-mixed plaster (RMP). This initial phase involved cleaning the surface by brushing to remove all pulverulent compounds contained in the surface parts. Next, a ray comprising a receptacle containing the RMP and tools needed for the handling process (scraper, cloth) was weighed (Mt before), as shown in Figure 4.  
The frame was then placed on the surface of the controlled sample to be tested, and the RMP was applied inside the frame with a scraper at the interface between the surface of the frame and the specimen surface (20 \(\times\) 10.4 cm\({}^{2}\)), which represented 208 cm\({}^{2}\) of the total area inspected. This process involved applying a bottom layer using a scraper with sufficient RMP and adequate pressure to ensure their good penetration at the base and to adequately cover all surface defects. Then, the frame was filled with RMP up to its edges (See Section 5.3). The RMP covering the surface was levelled using a scraper by shaking it periodically from one side to the other, distributing the RMP evenly along the surface frame/specimen surface interface. After the delineation of the RMP on the surface, the edges of the frame were wiped with a cloth to recover any RMP that was deposited during the application process. Once the plastering operations were completed, the cloth and the scrapers were automatically returned to their location in the tray. The tray was then weighed to determine the mass of the RMP deposited at the interface of the frame and specimen surface (Mt after). The mass of the RMP was determined as follows:  
\[\text{Mp}=\text{Mt}_{\text{before}}-\text{Mt}_{\text{after}} \tag{1}\]  
The mass of RMP that penetrated into the surface defects (Mpp) was calculated by weighing the RMP mass deposited at the interface of the frame and specimen surface (Mp) relative to the initial mass of the RMP (M\({}_{0}\)) applied inside the frame on a flat glass surface that was smooth and free of defects (reference medium), as shown in Figure 5. \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Compounds** & **SO\({}_{3}\)** & **CaO** & **SiO\({}_{2}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **Na\({}_{2}\)O** & **K\({}_{2}\)O** & **MgO** \\ \hline (\%) & 38.44 & 28.16 & 10.12 & 0.34 & 0.04 & 0.23 & 1.25 \\ \hline Density = 2.31 & & & & & & & \\ Setting time = 25 min & & & & & & & \\ \hline \end{tabular}
\end{table} 
Table 1: Physical and chemical properties of the plaster. Figure 4: Measurement of the RMP and materials used in the study. The mass of the RMP that penetrated (Mpp) was determined as follows:  
\[\rm{Mpp}=M_{P}-M_{0} \tag{2}\]  
where  
- Mpp: mass (in g) of the RMP that penetrated into the surface voids inside the contact surface area (frame/specimen surface), which represented 113.04 cm\({}^{2}\). - Mp: mass of the RMP (in g) deposited on the frame at the interface (frame/specimen surface). - M\({}_{0}\): mass of the RMP (in g) deposited on the frame at the interface (frame/glass surface); M\({}_{0}\) = 103.62 g.  
Knowing the mass of RMP that penetrated into all surface defects, we can then calculate its volume, which represents the volume of the defects. The calculation was made using the following equation:  
\[\rm{V_{defects}}=\frac{\rm{Mpp}}{\rho} \tag{3}\]  
where  
- Mpp is the mass of RMP that penetrated (g);  
- V\({}_{\rm{defects}}\) is the defect volume (cm\({}^{3}\));  
- \(\rho\) is the RMP density (1.845 g/cm\({}^{3}\)). The percentage of defects by volume was calculated in relation to 100% of the inspected area with the following expression:  
\[\rm{SDI}(\%)=\frac{V_{defects}}{V_{0}}\times 100 \tag{4}\]  
where \(V_{0}\) is the known volume of RMP deposited inside the frame placed on the glass surface (reference medium).