A friend just called me. Her brother was putting in a bathroom for them and got mad, so left the job unfinished. She was wanting help with tiling the shower. Here's what they've got:

Fiberglass neo-angle shower pan

Gypsum board-yes, regular gypsum board-for the shower walls. It stops about an inch shy of the top of the shower pan, and then has thin fiberglass tape in the corner and along the bottom of the drywall.

Hydro Barrier: very thin blue coat on the shower walls.

I've used Redguard but not Hydroban, so I'm no expert on the Hydro. But the backing needs to be cement board, no? I know you can Kerdi over drywall, but no Hydro, correct?

Just wanted to make sure before I tell them the good news that it needs to come out.