The effectiveness of bottom ash and heavy oil ash on the mechanical and physical properties of spraying mortar for fire proofing is investigated in this study. According to the analytic result of bottom ash, chemical composition of bottom ash was similar to those of fly ash. Therefore Physical properties of bottom ash including pozzolanic activity and particle size distribution were measured to decide the replacement amount in formulation. Laboratory test results concluded that inclusion of bottom ash increased the demand for mixing water in obtaining the required flowability but the compressive strength was not decreased in proportion by adding amount of bottom ash. Based on the results, bottom ash can be replaced with fine aggregate as much as 100% but adding amount of heavy oil ash is suggested as the below 10% in formulation.