This paper presents some results of an inspection program to detect coating-substract defects using a Michelson type of shear interferometer. Debonding defects are detected by properly loading the surface of the specimen in such a way that the interference fringe pattern is modified, rendering the debond readily visible. Image processing techniques are applied to enhance the detection and better define the debonding geometry. Load conditions, leading to a better detection of debondings, are also discussed. The technique allows to obtain information over a large area of the tested part, with a resolution one hundred of the wavelength of the light beingused.