Effect of Technological Variables on Thermal Conductivity and Compressive Strength of Hemp–Lime Composites

Hemp–lime composites are bio-based building materials with carbon sequestration potential, yet their properties exhibit significant variability depending on manufacturing variables, and standardized production guidelines remain lacking. This study investigates the influence of water-to-binder ratio (W/B = 1.75, 1.95, 2.15) and compaction degree (CD = 150%, 170%, 190%) on the thermal conductivity and compressive strength of hemp–lime composites using a full 3 × 3 factorial design at a binder-to-shiv ratio of B/S = 1:1. Results were synthesized with previously published investigations from a systematic research programme, enabling a comparative assessment of four technological variables across an extended dataset spanning densities from 227 to 518 kg/m3. The binder-to-shiv ratio was identified as the dominant factor governing both properties, primarily through its effect on bulk density and the mechanical character of the composite. Compaction degree was the most effective parameter for adjusting properties within a fixed mix design, with the strongest gains observed at the transition from CD = 150% to CD = 170%. The water-to-binder ratio exerted only marginal influence on bulk density and thermal conductivity, while its effect on compressive strength remained inconclusive at B/S = 1:1. Hemp shive particle size had a limited effect on thermal conductivity and no detectable influence on compressive strength. Both properties exhibited strong positive linear relationships with bulk density across the extended dataset. The findings support the standardization of hemp–lime composite production and the development of practical design guidelines.