In this presentation, an analysis of the bonding mechanism of adhesive mortars used in ETICS with thermal insulation and substrates will be presented, with a focus on how their adhesion is formed under real-life application. The factors influencing the adhesion of adhesive mortars to selected building substrates will be discussed. A newly developed method for testing the adhesion of adhesive mortars in laboratory conditions will be presented, taking into account the thickness of the adhesive layer, the type of substrate and thermal insulation, and the method of attaching the boards in relation to several different adhesives. A comparison of the test results with those obtained using the currently applicable method under the same conditions will also be presented.