Hi all,

Newb here, hope someone can help. Ok, here's situation.... I live in a townhouse. I have started the process to begin tiling a small shower. I removed an old acrylic modular type shower. I was left with broken up drywall, which I removed from all 3 walls. As it turns out, theres something called a "party wall" which has to exist between two units of a townhouse. The neighbor has to have this party wall, and so do I. It has to be 5/8" type X fire grade drywall.
Here's where my dilemma comes in. I have installed an acrylic shower pan which I intend to tile around. Since the back wall has to be the type X drywall, how can I waterproof this ????? BTW, this particular drywall is also mold resistant (purple). It's called Gold Bond XP.

Can I Red guard the drywall, then screw the CBU to it and also Red Guard the CBU?

Right now the only thing installed is this purple party wall and the shower pan.
Thanks for any help