## 2 Theoretical Discussion
### Tile Application Methods Comparison  
Spot-bonding is a method that commonly comprised of applying spots of adhesive at few large sections on the rear side of the tile. The type of materials used is usually a cement-based adhesive with a significant portion taken up by cement mortar with an unregulated W/C ratio. It is a commonly known problem that spot-bonding leaves substantial voids behind the tile (as shown in Figure 2). Based on the survey review, approximately 3-4 globs (generally in the corner sections) are applied, and the mortar is dispersed due to the pressing force of the worker to form a larger adhesion area. The need to conduct an individual application of adhesive on the tiles results in slower workability (7-10 m\({}^{2}\)/day) with usually higher adhesive thickness than the troweled adhesion method (20-40 kg/m\({}^{2}\), 10-25 mm thickness.) This typically results in an adhesion contact that is substantially less than the requirements of having at least 80% evenly distributed tile-to-adhesive support at the edges and corners [10]. As adhesive dispersion is generally dependent on the skills and strength of the worker, there is a limit in quality consistency for sections higher than the worker's height [11; 12]. In cases where workers are installing larger sized tiles, the weight of the tile and the cementitious adhesive increase the risk of adhesion failure [9]. The spot-bonding method is an applicable method, provided that the tile sizes are small. Recent trends in architecture have shown that tile sizes are not only getting larger, but also shapes are becoming more complex as well. However, studies showed that the usage of adhesive did not correlatively increase relative to the increasing size of the tile [7; 13], naturally increasing the risks of tile-adhesion failure or defect. This is because of the increased weight (if the adhesive is applied first onto the tile rather than the wall) and the amount of material used. The time, relative to the adhesive application, affects \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Items** & **Europe** & **U.S.** & **Asia (Korea and China)** \\ \hline Installation Method & Troweled adhesion method & Troweled adhesion method & Trowed adhesion method & Trowed adhesion and spot-bonding method (both) \\ Adhesive Material & Polymer & Polymer & Cement mortar, polymer (both) \\ Wall Type & Achieved smoothness from board, & Achieve smoothness from 1 st & Apartment: board, plywood finish \\  & plastering, etc., and set tile & plastering and set tile & Wall type: after brick, masonry cement \\  & & & mortar tile bond setting on 1 st plastered side \\ Related Standard & ISO 13007, EN 12004 & ANSI 108, EN 12004 & Requires more development to meet \\ Evaluation Standard & Bonding strength & & troweled-adhesion-method quality standard \\  & C1:0.5 N/mm\({}^{2}\), C2:1.0 N/mm\({}^{2}\) & Shearing strength 28d:1.03–2.76 MPa & Bonding strength 0.39–0.5 N/mm\({}^{2}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: International tile installation methods and related standards. Figure 2: Common spot-bonding method procedure: (**a**) mortar preparation for spot-bonding; (**b**) mortar setting (wall) for spot-bonding; (**c**) tile installation; (**d**) notched line and surface treatment. the construction work time. Refer to Figure 3 for sample images of how tile sizes have increased in recent years. On the other hand, the troweled adhesion method consists of initially applying the polymerized/ceentitious adhesive on the substrate wall surface (as shown in Figure 4), followed by applying a notched lining of the adhesive on the surface for securing a stable tile adhesion. The adhesion strength depends greatly on the type of polymer and admixture that are mixed into the adhesive material [14; 15].