I'm going to apply cement board over water proof sheet rock,anything special i need to do other than screw it
There is no such thing as waterproof sheetrock. The greenboard is water resistance at best. Make sure there is the correct waterproofing behind the sheetrock if you don't want problems in the future. Make sure your screw head are sunk flush so they don't hit the back of your tile.
Nope, just screw it on... fill the join cracks with durabond 90 and mesh drywall tape.
the cement board will be more effective and last years longer if it is attached directly to the wall studs instead of laid in over sheetrock .... even the water resistant greenboard has a shortened life in overly wet locations
Along with the screws I would use liquid nails. One tube per each 4 x 8 sheet.
Dont use green board. The first line on the spec sheet from any manufacture is do not use in tubs or showers. Use two layers of Hardi backer or Dens Shield. The Hardi is better but it is harder to cut. I have been in this business for years and I will only use one of the two listed above. G-P makes Dens Shield and they have the best warranty going. Use two layers of backer board attached with screws, tape the joints with mesh tape and durabond. Remember, grout failure is the reason most tile assemblies fail so check the grout and repair if needed, twice a year.
