Tape all layers when double plasterboarding

[PingCrosby]

Hi

My rooms have been boarded with 2 layers of 12mm. When joining new plasterboard to this do i need to apply tape to each layer seperately or is tape needed only on the top most layer.

The facing surface will eventually be half tiled and i dont know if need to allow for movement between the two layers of plasterboard.

Thanks for any advice

 

[Alastairreid]

Just the top layer.

 

[PingCrosby]

Cheers