This research aims to analyze the physical durability of oyster shells in hydraulic lime-based mortars. Standardized tests were conducted on mortars in fresh and hardened states using molds in the laboratory. The mortars produced were also applied to solid bricks and detached for further testing. The standardized specimens underwent a curing period of 28 days. The detached specimens, representing in-service conditions, also had a 28-day curing time in the laboratory plus accelerated aging curing. Two different types of mortars were investigated: a control group, and a group with a 30% replacement of sand aggregate by oyster shell aggregate. The study revealed distinct behaviors of the mortars in both laboratory and real-world conditions (after curing by accelerated aging, application, and detachment from the substrate). Key properties such as bulk density, open porosity, and water absorption were found to be influenced by actual service conditions. These nuances in behavior may not be readily apparent when studying mortars in standard molds alone. However, examining in-service conditions can provide valuable insights for optimizing dosage and incorporating new materials, thereby contributing to a more sustainable construction industry.