3D printing has emerged as a revolutionary technology with potential applications in the construction industry. However, the prevalent use of ordinary cement in most 3D printing formulations results in significant greenhouse gas emissions during 3D printing construction. In contrast, earthen-based composites are an eco-friendly alternative for building materials. However, as a construction material, earth presents poor mechanical strength and low durability against water erosion. This study aims to obtain earthen-based composites with suitable mechanical and durability properties to investigate their extrudability and buildability in tests. It also explores the effects of incorporating short sisal fibers (l/d ratio = 138.7) and chitosan (DD = 91%, M_w = 598 kDa) to improve strength and water durability in earthen-based composites for 3D printing purposes. Chitosan is a natural macromolecule derived from a waste product from the food industry, whereas sisal fibers are obtained from the Agave sisalana plant. The change in compressive strength was analyzed through uniaxial compression. Water durability was evaluated by measuring the water contact angle, total and capillary water absorption, and accelerated erosion tests. The results indicate that the use of 3.0% (w/v) aqueous solution of chitosan and 1.0% (w/w) of sisal fibers have an important effect on the hardening and water durability properties of earthen-based composites. This study suggests that these materials could serve as natural additives to enhance the mechanical properties and water durability of new eco-friendly construction materials for 3D printing. In conclusion, this study demonstrates that appropriate formulations with natural and eco-friendly additives can lead to stabilized earthen-based composites with suitable printing, mechanical and durability properties for 3D printing applications in construction materials.