I have removed an old gas interior fireplace from the living room and am left with a 3x5 foot patch of cement floor that is caked with old cement mortar from the original installation of the fireplace blocks. I have tried chisling it out but my body cant take much more of this. The old mortar is only about 1-2 inches high and unlevel. But as hard as steel. How can I remove this so that I can tile the area?