In this research work, experimental procedures by means of Transient Thermography and Holographic Interferometry were performed in order to detect subsurface tesserae areas of plastered mosaics. A mosaic sample consisted of various types of tesserae and covered with hydraulic lime mortar was evaluated in the laboratory with various transient thermal processing techniques such as Pulsed Phase Thermography, Thermographic Signal Reconstruction and Principal Component Thermography, as well as Holographic lnterferometry in both real-time and double-exposure configurations. Results from the non-invasive investigation are presented and discussed, revealing that the above approaches can obtain a seeing through investigation of plastered mosaics.