## 3 Experimental Regime
### Adhesive Dispersion Based on Different AR Conditions  
As a result of this experiment, it was confirmed that the smaller the adhered area, the higher the proportion of the adhesion strength of the center to the tile adhesion. Based on these results, the areas where it was possible to measure adhesion strength that was consistently the same for all three test specimens under the three conditions adhesive application area ratio (hereby labeled AR) of 60 \(\pm\) 2%, 80 \(\pm\) 2%, and 100% set in this study, are shown in Figure 13a-c. The schematic analysis (mapping) was performed as follows, based on the averaged results of the testing: in the case of specimens with cementitious AR 60 \(\pm\) 2%, the area where the adhesion strength could be measured was mainly located near the center of the tile, and the peripheral parts of these sections were mostly without any adherence (cavities with no bonding due to absence of adhesive support), as shown in Figure 13a. In the case of specimens with cementitious AR 80 \(\pm\) 2%, adhesion was again evidently concentrated in the center section and some in the peripheral parts, as shown in Figure 13b. In the case of specimens with AR 100%, while there were few pieces with cavities near the edge sections of the entire tile, successful adhesion was apparent throughout the entire specimen (shown in Figure 13c).  
The figures below show a mapping of tile pieces where the adhesion was apparent, overlapped with the results of all three specimens. Red color indicates pieces where the adhesion was common for all 3 specimens, pink color indicates pieces where adhesion was common for 2 specimens, and light-yellow color indicates pieces where adhesion was found for one specimen.  
Figure 12: Sectioned pieces adhesion strength (pull-off) evaluation method: (**a**) 60 \(\pm\) 2% specimen (units: mm); (**b**) 80 \(\pm\) 2% specimen (units: mm); (**c**) 100% specimen (units: mm).  
Based on the analysis of the tile pieces where the adhesion strength could be measured, it was found that adhesion strength increased relative to the increased concentration of the adhesive-applied area ratio (AR), but the adhesion strength was much lower at the corner and edge sections. In particular, it was confirmed that even if the bonded area formed over 100% of the entire area, the cavity sections where adhesion strength could not be measured were mostly shown to be forming at the edge sections. The AR of the adhered pieces and pieces with cavity (no adherence) are shown in Table 6 below.  
Based on the distribution of the adhered pieces for specimens with AR 60 \(\pm\) 2%, the area in which cementitious adhesive bonding was successful reached an average of 47.5% (difference of 12.5% from the AR ratio), and for specimens with AR 80 \(\pm\) 2%, the adhered piece ratio was 77.5% (difference of 2.5% from the AR ratio).  
This is an important point as workers or contractors were using spot-bonding with few applications of globs, mostly only on the corner sections of the tiles. The assumption followed that pressing the tiles would spread the adhesive, resulting in an evenly distributed adhesive throughout the negative side of the tile, but the results in Table 6 show that the adhesive distribution was far less than intended, and the mapped-out tiles with  
Figure 13: Adhesion ratio distribution map of specimens based on measurable adhesion strength pieces: (a) AR (adhesive-applied area ratios) 60 \(\pm\) 2%; (b) AR 80 \(\pm\) 2%; (c) AR 100%.  
secure adhesion and measurable adhesion strength was an indication of the risks of using only globs of adhesive for the spot-bonding method.