This study investigates the severe consequences of initial atmospheric exposure to iron-based alternative binders, focusing on the role of the addition of oxalic acid at various concentrations (0-4%) before the carbonation process. All iron-binder samples were subjected to 48 hours of pre-exposure to air, followed by 5 days of CO2 curing after the initial hardening phase. Mechanical strength and microstructural analyses were performed to evaluate the performance and the reaction phases formed. The results revealed that the addition of oxalic acid to the iron binder contributed to the carbonation and iron dissolution processes even after atmospheric exposure. Microstructural analysis revealed the presence of siderite (FeCO3) and calcite (CaCO3), which contributed to denser matrix formation for strength gain. However, Pre-exposure of already hardened samples to air led to non-uniform carbonation effects, where the outer surface carbonated, leaving the inner core of the samples resistant to CO2 penetration, resulting in variation in strength. Overall, the study also validates the role of carbonation in the iron binder system, where the curing protocols adopted in this study show ineffective and nonuniform carbonation, providing negative consequences to carbon-cured construction materials.