The integrity of organic coatings can be impaired by disbonding due to permeation of water in temperature and osmotic gradients between the outer environment and the metal surface or due to cathodic protection at locally destructed coatings. For thin coatings the degree of delamination is easily determined by the intensity of blisters which generally arise already after short exposure periods. However thick coatings with thicknesses above 2 mm take much longer for blistering and larger delaminations and develop visible blisters only in an advanced state. The degree of delamination can generally be investigated only with mechanical destruction of the coating. The present paper presents a new non-destructive test (NDT) method for detecting delaminations and blisters in or under organic coatings with thicknesses up to 5 mm using active IR thermographic methods with induction and/or optically excited lock-in thermography. The methods have been specifically modified to allow the localization of delaminations in and under thick coatings already at stages when the defects are not yet visible. The potential of the method is exemplified for cases of blister determination under Delta-T test conditions and for the non-destructive quantification of the length of delamination after standardized cathodic disbonding tests.