# Effect of Injecting Epoxy Resin Adhesive into Cement Mortar on Tile Adhesion Performance
## 1 Introduction  
The increased construction of large buildings and burgeoning interest in interior and exterior designs have fostered a shift in the demand for small ceramic tiles to large esthetically appealing porcelain tiles. Conventional ceramic tiles are porous and exhibit a high absorption rate. However, superior adhesion performance is achieved through mechanical fixation when cement hydrate is deposited within the pores [1, 2]. In contrast, porcelain tiles are fouling-resistant and are less susceptible to damage from moisture expansion and freezing due to the existence of minute pores, which make them essentially nonporous compared to ceramic tiles [2, 3, 4]. Unfortunately, the minute pores of porcelain tiles result in a smooth rear surface, thereby making it difficult to achieve strong adhesion of the tiles using ordinary mortar [2, 5].  
Therefore, plasticing techniques using polymer-based adhesives are being extensively adopted in many countries to enhance the adhesion performance of porcelain tiles. However, the use of dry cement mortar and bedding techniques remains popular because surface finishing is often omitted in many countries, including South Korea, due to economic reasons. Various polymer-based adhesivesare applied, some of which are not used judiciously. Consequently, the adhesion and internal strengths of the adhesives are considerably reduced, resulting in delayed curing, contraction, and expansion of the adhesives, which negatively impact the construction quality.  
In fact, according to the National Assembly's Transportation Committee in South Korea, tile defects have accounted for the largest proportion (34.5%) of defects in the apartment construction of Company A over a period of three years (2015 to 2017). Further, the number of international cases of floor and wall tile failures has also been increasing ([PERSON], 2016; [PERSON], 2018; [PERSON], 2019). Tile defects can cause the tiles to fall off within living and working spaces, thus raising safety concerns for individuals. Moreover, the additional costs of demolition and reconstruction increase the economic losses, and considerable construction waste is generated, along with noise and scattering dust when the tiles are dismantled, thus resulting in inconvenience and negative environmental impact. Therefore, it is necessary to achieve an improved tile with more reliable adhesion performance during construction.  
Previous studies have reported that the application of cement-type adhesive mortar (e.g., dry cement mortar) to large-sized tiles can cause cracks as a result of the concentrated stress owing to changes in the volume during shrinkage and expansion ([PERSON], 2019; [PERSON], 2019). To mitigate this type of construction defect, epoxy resin was used in this study. In addition to the advantages of high adhesion strength and low shrinkage, [PERSON] et al. postulated that epoxy resin cures through chemical adhesion with cement mortar, and provides restorative effects by penetrating and curing within the cracks ([PERSON], 2019; [PERSON], 2019). These advantages of epoxy resin are expected to be particularly beneficial in constructions that utilize dry cement mortar as the tile adhesive.  
Herein, we review the applicability of the proposed method of injecting an epoxy resin adhesive between the tile joints (Figure 1) during the conventional curing process, without extending the construction period (Figure 2). Further, the bisphenol A-type epoxy resin was utilized and the viscosity and permeability at various solvent mixing ratios increased the workability and adhesion efficiency by injecting the epoxy resin. Subsequently, the mechanical and dry shrinkage properties of the selected epoxy resin adhesive were confirmed based on the penetration results, and the adhesion performance of the tiles was evaluated.  
Figure 1: Outline of epoxy resin injection for reinforcement.  
Figure 2: Process of epoxy resin reinforcement.