Towards 3D Printing of Cob-Based and Hemp-Based Material Mixtures for Home Building: A Manual Extrusion Experimental Study

This paper presents an experimental study of extrudable cob-based and hemp-based materials as an initial step toward their use in 3D printing. Cobcrete mixtures containing clay, sand, lime, straw, water, and selected additives and hempcrete mixtures containing hemp hurd and a lime-based binder, were prepared and evaluated. Laboratory tests examined the preliminary extrusion behavior of selected fresh mixtures and the compressive, splitting tensile, and flexural responses of cast specimens. Three specimens were tested for each reported formulation and age. The cobcrete formulations reached mean 28-day compressive strengths of approximately 0.52–1.49 MPa, while the hempcrete formulations reached mean 7-day compressive strengths of approximately 0.05–0.34 MPa. Manual syringe and pump extrusion was used to compare material handling, extrusion continuity, and short-term layer retention as a preliminary step before controlled robotic trials. Because some constituent proportions changed simultaneously, the results were interpreted as comparisons among complete formulations rather than isolated effects of individual ingredients. The study identifies candidates for subsequent rheological characterization, controlled robotic printing, interlayer testing, and durability evaluation.