Plaster mortar aims to develop technical and practical needs with indigenous construction practices as per locally available materials for pneumatic plaster machines. The study investigates the feasibility of plaster mortar using GGBS and crushed sand as viable supersede of cement and natural river sand, respectively. The study proposes better results by 100% supplantation of river sand with crushed sand and partial replacement of GGBS with cement. The mortar mix designs for pneumatic plastering machine cement are replaced with GGBS with proportions such as 20, 30, and 40%.The mix designs cast for the slump of 270–300 mm were tested for various site conditions. The samples of 70.6 mm mortar cube,160 × 40 × 40 mm beam, and radius 50 mm × 100 mm height cylinders are considered for the compressive, flexural, and split tensile tests. These tests are carried for the curing age of the 7th day, 14th day, and 28th day. Durability tests are carried for immersing the samples in NaCl solution and MgSO4 solutions creating adverse site conditions. Test results revealed that mix design with 20% GBBS replacement by cement quantity showed commendable results in mechanical strength. A specialized plaster mortar formulation suitable for use with a pneumatic plaster machine is developed, optimizing for efficient application, adhesion, and finish quality.