Thermally conductive cementitious compositions for use in flooring installations that are applied over a heat radiating flooring system to increase the thermal conductance of the flooring system and increase the rate of heating the flooring system. The thermally conductive cementitious compositions include a cementitious composition, amorphous flake graphite carbon, and an aqueous solution suitable for use as a thermally conductive mortar, grout or adhesive for flooring installations. The thermally conductive cementitious compositions also include a cementitious composition, mesh fine aluminum oxide, mesh coarse aluminum oxide, and an aqueous solution that provides a thermally conductive mortar, grout or adhesive for use in flooring installations.