Abstract In most countries, waterproofing systems used on concrete bridge decks or roofs of buildings are generally based on orthotropic bituminous membranes; amongst these, styrene–butadiene–styrene copolymer (SBS) and atactic polypropylene (APP) polymer modified bituminous membranes are being used in most applications. One of the main technical concerns is the formation of blisters under the membrane caused by a complex mechanism governed by bottom-up pressure and loss of adhesion. This paper intends to contribute in understanding this mechanism by mechanical elastic modeling and experimental investigation. In order to study the material properties of SBS membranes under the in-plane complex stress state, the orthotropic mechanical behavior of a polymer modified bitumen membrane (PBM) was determined from biaxial test data. Hence, the measured stress–strain data were analyzed using the orthotropic equation to find the material properties in the longitudinal and transversal direction. Finally, blister tests were performed on concrete plates for studying adhesive blister propagation by applying controlled pressure between the PBM and the concrete plates. It was found that the ratio of the longitudinal to transversal adhesive blister propagation is comparable to the ratio of the modulus of elasticity in the longitudinal to transversal direction. Due to the orthotropic material property of the PBM, elliptical adhesive blister propagation was observed and a new model proposed for determining the energy for elliptical adhesive blister propagation.