Should I rock over the plywood
 

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.

A house that old most likly has 24" on center ceiling joist, so no, thin rock is not going to cut it.
I'd use sheetrock glue and 2-1/2" cource drywall screws.

Your going to have to locate the joist not just screw to the plywood.

Rent or borrow a drywall lift.

If it is plywood sheathing not paneling, it may be stronger. Use 1/2" to be safe, as Joe said, but only 1-3/8" screws are required into the c.j. through the 1/4"- Table 3: http://www.lafargenorthamerica.com/GA-216-07%20English.pdf

Gary

If the cieling joists are 24" on center you should use 5/8 drywall or it will sag.

Just so we're clear. . .