Understanding material properties is fundamental to the structural assessment of existing buildings. In the case of masonry constructions, this characterization is particularly challenging due to the high variability in materials, construction techniques, and the influence of ageing and previous interventions. These challenges are exacerbated by the limitations of in-situ testing, particularly in heritage structures, where intrusive methods are often restricted. Over recent decades, the Portuguese technical and academic communities have made substantial efforts to characterize masonry typologies. However, these initiatives have largely been fragmented and uncoordinated, limiting their potential to inform national and international standards. This paper presents part of the ongoing work of the Working Group under Sub-commission 8 (Eurocode 8) of CT115 (Portuguese Technical Commission for Structural Eurocodes). The group has compiled and systematized data on masonry elements’ mechanical properties from academic research and professional practice into a unified, freely accessible database. A key outcome of this work is the development of new analytical expressions that correlate mechanical parameters—compressive strength, shear strength, elastic modulus, and shear modulus—with the Masonry Quality Index (MQI), a semi-quantitative indicator of masonry construction quality. These expressions provide a practical basis for the structural assessment within the future generation of the Portuguese Annex of EC8-3, supporting a more robust and harmonized evaluation of Portugal’s masonry building stock.