Infrared thermography is a well-established technique for evaluating material properties through thermal measurement. In this paper, the thermographic principle of debonded building-finish system is proposed based on laboratory calibrations. An effective approach is developed to eliminate the disturbance of reflection. The survey results prove that this method is reliable in detecting the debonded ceramic tiles on a building finish. With defective areas appearing differently from well-bonded regions, as a result of their differential transmittance of infrared (IR) radiation, the large surfaces can be rapidly scanned. The proposed approach makes it possible to perform interpretation and analysis with a high degree of accuracy.