# Hammering Test for Tile Wall Using Deep Learning
## 3 Non-Destructive Test for Adhesive-Applied Tile Wall  
### Hammering Test  
Huge structures, such as bridges, dams, and buildings, are made of concrete. In addition, low-rise buildings such as apartment buildings are often covered with tiles for decorative purposes. This paper focuses on a technique for testing the adhesive-applied tiles for exterior use. If the adhesion rate of a tile is low, the tiles may fall off and injure people walking near a building. Traditionally, mortar has been used as an adhesion method for exterior tiles. However, in recent years, adhesives have increasingly been used. In Japan, Article 12 of the Building Standard Act [13] mandates that a \"visual survey and partial hammering test\" be conducted every two or three years and a \"full hammering survey\" every 10 years. * Visual survey: This test involves observation of the exterior using the naked eye, binoculars, telescope, etc., and a hammering test of the area within reach using a test hammer. * Full hamm ring test: This test consists of a hammering test using a test hammer or an infrared survey. In Japan, the number of apartment rooms is about 6.4 million and there were 0.12 million apartment buildings in 2022 [14], so that it is required 12,000 apartment buildings should be checked every year. The infrared survey measures the surface temperature of tile surfaces using an infrared imaging device to determine sound and cavity under tiles. This method can be used when the area of the cavity is large, as in the case of mortar tile walls. However, it is difficult to detect small cavities, as in the case of adhesive-applied tile walls. Figure 2 displays the difference in the cavity behind a tile wall. In the case of the tile wall with mortar, the cavity behind the tiles is large; on the other hand, in the case of an adhesive-applied tile wall, the cavity is small. So, it is difficult to detect cavities behind the adhesive-applied wall. In inspections of mortar tile walls, not only a hammering test but also an infrared inspection is used. However, in the case of adhesive-applied tile walls, it is difficult to detect cavities using infrared inspection because the cavity is small. Therefore, a hammering test is necessary for adhesive-applied tile walls. However, the adhesive absorbs the sound caused by the hammer, making it difficult to distinguish the difference in sound. Recently, a technique to use microwaves has been developed [15]. The problem is measuring time. In [16], it is mentioned that it takes 30 s to test a tile using a microwave; on the other hand, it takes 0.3 s using the hammering test. So, the hammering test is the only method available. So, we have started to develop an AI-based hammering test for adhesive-applied tile walls. Figure 2: Tile wall applied using mortar and adhesive. The Architectural Institute of Japan (AIJ) publishes _JASS (Japanese Architectural Standard Specification)_, which is a standard specification for building construction. In _JASS19_[17], page 163, it is mentioned that the rate of an adhesive-applied tile should be 60% or more. Therefore, it is important to distinguish whether it is over 60% or not, and it is not necessary to estimate the adhesion ratio exactly. This research aims to develop an AI model to determine whether the adhesion ratio of a tile is above or below 60%. It is not necessary to accurately determine adhesion rates such as 100%, 80%, 50%, 0%, etc. A tile hammering test tool (hammering rod) for tile walls is shown in Figure 3. It consists of a steel or plastic rod with a 17-19 mm steel ball attached to the end of the rod. They weigh 70 to 200 g and are 130 to 2010 mm in length, and the price is between USD 15-USD 30 [18]. On the other hand, the price of a typical piece of infrared thermography equipment costs between USD 1500-USD 3000 [19]. So, the hammering test device is cheaper than other test devices. Although there is no clear national standard for inspection tools used in the hammering test for tile walls, these tools are a de facto standard.