In process of laying hardwood floor in 2nd floor hallway and will continue down stairway. The stairway is currently carpeted which has been removed. Must I remove the current MDF treads and risers(because of built-in bullnose) and re-do with plywood or can I pack out and square off with new plywood on top of current treads and risers? If I must remove the current MDF what is the best way since it is now nailed and glued and seems like it would be very difficult. Thanks