To enable prediction of the strength of polymer mortars, a failure model is presented. Based on the so‐called Arrhenius kinetic rate equation, a compound dual failure criteria is developed. The proposed model considers the visco‐elastic nature of the class of materials manifested by the dependence of their strength on loading rates and temperature. The model also accounts for the class's dual failure modes as a rock/soil/concrete‐type material, i.e., failure in compressive shear and/or tensile cleavage. Experiments were performed with mortar specimens using several different epoxy binders. Benchmark values of parameters of the proposed failure model are presented. Within the range of temperatures and loading rates used in the experiments, the model appears to comply well with experimental data. It is anticipated that a similar failure model can be used for mortars made with other types of polymer binders and for polymer concrete in general.