This research work aims at studying the influence of fermented organic additive on strength and carbonation of air lime mortar for the conservation of heritage structures. Binder to aggregate ratio of 1:3 by weight and water to binder ratio of 0.7 were considered. Red grape (Vitis vinifera) as an organic additive with 2, 4, 6, 8 and 10 percentages were accounted for fermentation of 0, 1, 2 and 3 days and were added with lime mortar. Experimental investigations were conducted on mechanical and mineralogical properties. 6% of organic addition with 3 days of fermentation resulted in a 49% increase in the mechanical resistance compared to the reference mortar on 90th-day test. XRD records an increased calcite formation due to accelerated carbonation. FTIR indicates the presence of polysaccharides that have helped in accelerating carbonation. TGA-DTA supports XRD and FTIR results in confirming the strength gain through the formation of calcium carbonate. Hence, the results are explicit, revealing that the fermented organic addition in air lime mortar has increased the carbonation rate, as the polysaccharides present in organic played a crucial role in accelerating the transformation of calcium hydroxide to forms of calcium carbonate and thereby enhancing the strength significantly. © 2020, © 2020 Informa UK Limited, trading as Taylor & Francis Group.