In masonry construction, effective bond between mortar and unit is required in order to provide structural integrity and durability to the masonry assemblage. Bond is dependent on material properties, workmanship, curing environment and age. The present research work aims at improvement of the long-term performance of masonry load-bearing structural elements exposed to harsh environmental conditions through use of different mortar constituents. An experimental program was conducted in order to investigate the effect of varying the mix constituents and proportions on the bond strength between mortar and clay bricks subjected to different exposure conditions. Local clay masonry units were used and ten different mortar mixes were investigated. The studied additives are lime, silica fume (SF) and polypropylene fibers (PPF) with different ratios. The specimens were exposed to harsh environmental conditions of wetting-drying cycles of water and sulphate salts solution, and the long term performance is compared to control specimens left in air. Tests were made to determine the mortar and prism compressive strength of mortar and the bond strength. The experimental results indicate that adding SF or PPF with a percentage of 2% to 5% of cement weight significantly improves the bond strength and deterioration resistance.