Masonry structures behave in a heterogeneous manner since they consist of different materials (i.e., blocks, mortar, grout, and reinforcement) with different mechanical properties. This makes their behavior more arbitrary, complicated, and challenging to predict due to the presence of various components. Although there is a considerable number of experimental investigations for masonry prisms in the literature, these investigations mainly focused on the ultimate capacity and corresponding strain, whereas complete data, including the post-peak behavior, is minimal. The interpretation of the complete compressive stress–strain curve of fully grouted and ungrouted web and boundary element assemblages is essential to understand the response of reinforced masonry shear walls (RMSWs) as structural elements subjected to lateral forces. Therefore, this study presents an experimental investigation of the mechanical properties of masonry assemblages under axial compression loading. Twenty-eight masonry prisms were constructed and tested to investigate the axial compressive response of fully grouted, ungrouted, and boundary element masonry assemblages according to CSA S304-14. Additionally, 100 × 200 mm cylinders of grout and 50 mm mortar cube specimens, sampled during the construction of the prisms, were tested according to CSA A179-14 and ASTM C109M-13, respectively. The results provide complete compressive stress–strain curves for grouted, ungrouted, and C-shaped boundary element prisms. The results showed that the ungrouted prisms have higher peak compressive stress than their grouted counterparts. Moreover, the boundary element prisms demonstrated relatively higher compressive strength than fully grouted web prisms.