Hempcrete, a bio-composite material known for its excellent thermal efficiency, is gaining traction in the construction industry as an environmentally friendly alternative. However, the binder component used in the hempcrete has long been a debated issue among researchers. This paper aims to explore the influence of SCMs on the thermal and mechanical performance of hemp-lime composites. The study utilized lime-based binders incorporating slag, which is an industrial by-product, to evaluate its effect on hempcrete specimens. Hydrated lime was partially replaced with slag in proportions of 20%, 30%, 50%, and 100%, with lime binder hempcrete serving as the reference sample. The binder-to-hemp ratio was maintained at 1:1 by weight, yielding an average density of 190 to 200 kg/m3. The hemp shives were also ground finely to minimize their impact on the results and reduce variability. The findings indicate that incorporating slag into the binder enhances both the mechanical strength and thermal resistance of the material while reducing its heat capacity. However, a higher slag proportion in the binder was found to affect compressive strength inversely. This outcome offers new insight into a better understanding of binder combinations in hempcrete.