This paper presents the results of a study that evaluated the accumulation of marine salts in the metropolitan area of the port city of Chittagong in Bangladesh, and their effects on specimens made from five different types of mortars normally used as external renders for built infrastructures such as buildings and bridges. Mortar specimens were exposed to atmospheric environment at 12 monitoring stations scattered around Chittagong’s metropolitan area. Mortars were made (using combinations of cement, lime, volcanic ash, and fly ash) with variable water-to-binder ratios and cement/binder content. The performance of the mortar specimens was evaluated based on marine salt accumulation and resistance to marine salt penetration. The amount of salts (Cl− and captured in powdered samples extracted from mortar specimens was determined using ion chromatography. Laboratory tests such as mercury intrusion porosimerty (MIP), differential scanning calorimetry (DSC), accelerated chloride ion diffusion (ACID), and electrical resistivity (ER) were conducted on mortars, in addition to tests on fresh and hardened properties of mortars. Test results showed that the marine salt accumulation was significant up to a distance of about 200 m from the seashore. The analysis of accumulation and subsequent penetration of marine salts in exposed specimens identified the mortar types that are more resistant to the aggressive potential of the region’s marine aerosol. The results suggest that volcanic ash and fly ash based mortars can provide better salt penetration resistance than cement based mortars. Recommendations of this study will be useful for local authorities engaged in selecting protective measures (in terms of external renderings) to improve the durability of infrastructures exposed to marine salts.