Someone put 1/4 plywood on the ceiling of the bedroom of my home that was built in 1941. It is an addition to the original house and in good condition using box nails it is secured well to the ceiling joists using a pretty uniform though not code nailing convention. My question is should I just rock over it probably getting frustrated with screws hitting nail heads from time to time or pull it all down to the joists? And if so is 1/4" rock thick enough or should I go 3/8"? Thanks in advance.