## 3 Experimental Regime
### Adhesion Testing Method Preparation  
The ISO standard evaluation was conducted according to the adhesion strength test method compliant to ISO 13007-2. A total of four separate pull-off apparatus plates (attachment pieces) were applied to the tile surface using an epoxy bond on a tile specimen of 50 \(\times\) 50 mm size, two on the center sections (labeled Number 2 and 3), and two at the  
Figure 5: Spot-bonded mortar adhesion surface area determination process: (**a**) spot-bonded mortar; (**b**) adhesion on to concrete surface; (**c**) thermal emission imaging; (**d**) digital mapping. outer sections (labeled Number 1 and 4), as shown in Figure 6. The adhesion attachment strength for each installed tile piece was measured by applying a pull-off load at a speed of 250 \(\pm\) 50 N/s using a UTM apparatus (Kyungsung Testing Machine Co., Ansan, Korea). This testing was repeated with five separate such specimens in order to confirm the change in the adhesion strength of the cementitious adhesive according to the applied area. The results of adhesion strength evaluation conducted according to the adhesion strength test method of ISO 13007-2 are as shown in Table 5 and Figure 7 below, and the results showed that the strength was less than the ISO standard (0.5 N/mm\({}^{2}\)), and the specimen number 4 (70%) showed about 175% adhesion compared to the ISO standard. Figure 7 shows that the adhesion strength results varied in accordance with the location numbers, where light blue (1) and purple (4) were on the edges, and orange (2) and gray (3) were in the center sections. The results confirmed that the edge sections of all specimens (No. 1 to 5) had lower tensile strength than in the center. As a result of this analysis, the difference between the adhesive strength (average 1.31 N/mm\({}^{2}\)) of the central part (specimen No. 2 and 3) of the tile and the adhesion strength (average 0.44 N/mm\({}^{2}\)) of the edge part (No. 1 and 4) was about 0.87 N/mm\({}^{2}\). As a result of examining the negative \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Specimen Number**} & \multicolumn{5}{c}{**Adhesion Strength (N/mm\({}^{2}\))**} \\  & **No. 1** & **No. 2** & **No. 3** & **No. 4** & **No. 5** & **Avg.** \\ \hline
1 & 0.76 & 1.06 & 0.21 & 0.61 & 0.31 & 0.59 \\
2 & 1.43 & 1.44 & 1.32 & 1.48 & 1.19 & 1.372 \\
3 & 0.93 & 1.51 & 1.27 & 1.31 & 1.25 & 1.254 \\
4 & 0.14 & 0.14 & 0.24 & 0.50 & 0.39 & 0.282 \\ Average & 0.82 & 1.04 & 0.76 & 0.98 & 0.79 & 0.878 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Adhesion strength result of the specimens based on ISO standard evaluation. Figure 6: Specim and test method illustrated for the ISO (International Standard Organization) standard pull-off test. Figure 7: ISO standard adhesion strength evaluation results. side of the tile after the test (shown in Figure 8), it was found that the edges of the No.1 and 4 pieces had a lower adhesion surface than the central parts of the No. 2 and No. 3 pieces. This result was similar to [PERSON]. [PERSON]'s (2010) previous study [1], and it was judged that the adhesion of the edge portion was formed lower than that of the central portion. As expected, the results of this precursory experiment indicated that the dispersion of the adhesive on the negative side interface of the tile did not reach the edge sections of the tile, and there was about three times the difference of achieved adhesion strength between the center sections (Number 2 and 3 tile pieces) and the edge sections (Number 1 and 4 tile pieces). In this regard, it was confirmed through this precursory testing that served to validate that the normal ISO standard evaluation procedure was not sufficient to provide a concise evaluation of the overall adhesion stability of spot-bonded tiles and that a new evaluation method must be designed.