Waterproofing in Victoria

Waterproofing procedure help.

My shower's tiling has been partially ripped up and left to air out for awhile as the damp smell was overwhelming coming from behind the tiling even when we weren't using it and I'm trying to find out the correct way to redo the waterproofing before the tiles are replaced.
I can see the paint type waterproofing on the walls and its been ripped off completely in spots and bubbling/cracked off in others. Should the waterproofing be taken off and redone? There's a damp smell coming from under the waterproofing but builder wont agree to take wall off and do it properly.

Is the tiler able to do waterproofing in Victoria or is a certificate required because they don't seem to even think waterproofing is useful.

I'm a tiler in Wa and I recommend that you would scrape the old waterproofing of and get it re done the tiler should be able to do it