The paper reports values of surface free energy and its components of an epoxy adhesive modified by the addition of an active diluent. Wetting envelopes are determined and they serve as a basis for a wettability analysis and determining the possibility of maximizing the work of adhesion between the liquid and the solid. Static strength tests of adhesive joints made with the analysed adhesive compositions were also conducted. The results are used to determine the effect of active diluent addition on the energy and adhesive properties of the epoxy adhesive.