This study is regarding the property evaluation of mortar for ‘ONDOL’ floor (Korean floor heating system) finishing with reduced drying and shrinking properties to use it in the form of ready-mixed concrete mortar. The mortar utilized furnace slag based inorganic binding agent NSB, which has the characteristic of CaO included in HCFA generated from the fluidized-bed-firing power plant. Based on the test results, it is judged that mortar for ‘ONDOL’ floor finishing based on NSB including HCFA can be used in the form of ready-mixed concrete. According to site test construction, the flow property was relatively poor because fine gravel at ready-mixed concrete factory was used. However, since finishing property, crack resistance and water content are good, it is believed that it can be used at construction site in the form of ready-mixed concrete mortar. More study on adhesion property with floor plate would be required in the future.