The work reports the experimental use of Infrared thermography (IRT) to detect embedded defects in mortar specimens. Surface temperature patterns are collected and compared with numerical solutions. The numerical formulations are based on frequency domain approaches using the coupling between the boundary element method and the method of fundamental solutions. Circular cylindrical ring and parallelepiped specimens incorporating thin defects are used. The heat diffusion within the test specimens is induced by line heat sources placed on their axes.