Hand-applied plaster in joints of moisture-resistant gypsum?

[JimmyB]

Renovating the bathroom and have put up the drywall. Before applying the barrier layer and tiling the walls, I thought about leveling and filling the joints between the boards.
I see that you can use tape and putty. However, I wonder if I can use tape together with Knauf handputsgips instead? I happen to have some of that left over and not so much putty, so if it works just as well, it would be nice.
Grateful for advice
Jimmy

 

[Jonatan79]

Follow the waterproofing manufacturer's instructions so there won't be any problems in the future.

 

[Stefan N]

Gypsum plaster is too weak. Leave it as is and use fix to fill when you install instead.

 

[Fred vom Jupiter]

Gypsum plaster is too weak. Leave it and use mortar to fill when you apply instead.

Knauf Rotband hand gypsum plaster is approved as a base for tiling as far as I know. Commonly used.
Does it become too weak specifically at the board joints?