New build bath tiled with mastic and no waterproofing?

Hi there, long time lurker, first time poster. I’ve recently moved in to a new build property which looks like it was built on a late friday afternoon.

I wasn’t keen on the bathroom tiles so decided to redo the whole bathroom walls and floors.

After removing the bath wall tiles I noticed there doesn’t seem to be any waterproofing, also the tiles that were installed (can be seen in picture) seem to have been attached with tubbed mastic which I thought was a big no no in wet areas.

As you can see in the pictures it was tiled over skimmed and painted plasterboard (which I thought was also a no-no).

I accidentally made some holes in the plasterboard when removing the tiles and it seems to have that green paper layer if that makes any difference.

Am I right in saying this installation is against regulations and do I have a leg to stand on if I complain?

As I was planning on tiling the whole bathroom with 600mm x 900mm porcelain tiles I have removed the paint from the outer bathroom walls and gone over with a few coats of SBR but im not sure how to approach the bath area (assuming the builders wont do anything about it)

Should I :

A) remove all mastic, patch up holes, use a Mapei tanking kit (without removing bathtub)

B) Bite the bullet and remove all plasterboard and replace with something like this with taped seams:


Thanks!

Bonus question, I was planning on adding a niche into the long side of the bath’s wall but after checking there is only 70mm depth inside the wall, do they make niche trays to fit or should I go to the far end wall away from the showerhead which has 120mm+ depth? (But will be annoying to use)

There is always the option to custom make your own. I found this little tutorial on youtube that may help
View: https://www.youtube.com/watch?v=a0KQZX-7czU&ab_channel=SalDiBlasi