Abstract The performance of commercial wood chip (WC) and biosolid (BS) biochars available in bulk from carbonization processes in South Korea was examined via determination of sorption capacity from batch experiments and evaluation of carbon sequestration using biochar–mortar composites according to construction and environmental properties. Compared with rice straw (RS) biochar synthesized in a laboratory, the sorption capacities of WC and BC biochars are determined by the types of contaminants, the properties of the biochar, and sorption mechanisms. BS and WC biochars are competitive as sorbents for nitro explosives and chlorinated phenols. Characterization of biochar–mortar composites showed that 3–5 wt% biochar inclusion did not significantly change the composites' engineering properties, including flowability, compressive strength, and thermal conductivity. As the biochar content increased in the biochar–mortar composites, the benzene and toluene concentrations in air were accordingly reduced, suggesting that biochar inclusion may be favorable to remove volatile toxic contaminants that cause sick building syndrome. The toxicity characteristics leaching procedure (TCLP) and Micotox® bioassay tests showed that biochar–mortar composites were not toxic. These results suggest that BS and WC biochars in South Korea are competitive as sorbents for some organic contaminants and that biochar–mortar composites may be environmentally friendly carbon‐sequestering construction materials.