Toolpath as tectonic: experimental investigation of fabrication-integrated stability in earthen additive manufacturing

Purpose Additive manufacturing has renewed interest in earth as a construction material, removing dependencies on skilled labour and formwork while opening geometric possibilities beyond the reach of traditional methods. Yet freshly printed earthen material must support successive layers before consolidating, limiting continuous build height and undermining fabrication continuity. This paper proposes and evaluates periodic toolpath modulation (PTM) as a process-integrated strategy to improve wet-state buildability through fabrication logic rather than material modification. Design/methodology/approach Through a Research-through-Design methodology, a clay analogue experimental program was conducted across five sequential phases. Sixteen configurations were tested by systematically varying key toolpath parameters under constant material and machine conditions, isolating the influence of toolpath design and sequencing logic on wet-state stability. Findings Three governing conditions were identified: sinusoidal toolpath geometry, balanced phase alternation and continuity of the alternation sequence. When all three are satisfied simultaneously, the optimal configuration achieved a 63% improvement in continuous print height over baseline. Failure character also differed, shifting from a sudden collapse with no prior deformation to a gradual failure that gave observable warning during printing. Originality/value To the authors' knowledge, no prior study has systematically examined PTM as a wet-state stabilisation strategy in earthen additive manufacturing at the toolpath geometry and sequencing level. It repositions toolpath design as an active fabrication variable rather than a downstream technical step, offering a process-based alternative to material modification that would otherwise compromise the recyclability and low embodied carbon of earth. As a first controlled study, it establishes a basis for fabrication-integrated stabilisation, to be validated on variable site-excavated earth.