Common material systems used for 3D printing of sand-casting moulds are often plaster-based sand compositions with typical limitations. Bentonite-based sand composites and associated binding mechanisms are well established in traditional foundry practices, but possible use of similar systems is scarce in 3D printing. The current research attempts this, considering bentonite-sand composites of varying compositions for 3D printing and evaluating the mechanisms and mechanics of bonding. Differing amounts of α-hemihydrate together with varying quantities of terra alba as the seeding agent are identified to be effective together with impregnation by sodium silicate and subsequent baking at suitable temperatures. The bonding in green state is achieved through gypsum crystallisation and assisted by terra alba as the seeding component. Sodium silicate soaking and impregnation increased the compressive strength notably (1.3MPa) from green (0.49MPa) and directly baked without sodium silicate impregnation (0.19), with almost 2.7 fold increase from the green compressive strength and 7 fold from the directly dried case.
