Over the past few years, there has been a growing trend towards selecting environmentally sustainable construction materials. The incorporation of natural or recycled materials in the construction sector is developing. One particularly promising material is hydrochar, a byproduct of the biomass hydrothermal carbonization process (HTC). The focus of this research is to conduct a thorough multiphysical analysis of cutting-edge cement and lime-based plasters that include activated hydrochar. This innovative approach not only allows for the repurposing of waste but also increases the porosity and surface area of the resulting material. Thermo-acoustic property evaluations were carried out on three samples containing 2%, 4%, and 8% by weight of activated hydrochar, respectively. Additionally, a comparison was made with a sample containing 4% non-activated hydrochar. The results showed that the presence of hydrochar in the plasters led to a decrease in thermal conductivity and significant improvements in acoustic transmission loss. In conclusion, this research highlights the potential of utilizing hydrochar in plasters as a sustainable solution for building applications.