Let’s get it clear that I’m not saying I wouldn't use backer boards in a wet area or disagreeing it has added benefits over tanked plasterboard. It's just that I don't think tanked plasterboard is 'un-suitable' like you say.
Here are my reasoning why in the op's situation I would go with tanked PB
It's not because it's cheaper, in fact I doubt it is, plasterboard + tanking kit is probably similar in price to just buying backer boards. It is however easier to work within the OP's case. The shower I should imagine is maybe something
standard like 900x900 and he's already stated he doesn't want to disturb surrounding areas, with plasterboard you can install in one piece floor to ceiling with no joints, with the average backer board being 600x1200 and the dimensions given you would have to lay the BB's horizontally meaning you would have 4 boards floor to ceiling with additional joints (assuming normal height ceilings) with thicker backer boards you could get away with not adding noggins on each joint but with the 12mm boards I wouldn't feel comfortable not adding extra support, fine you can do that but it is slightly more work and in addition you have the pipe work to contend with. No big problem but it is something else needed.
You mentioned PB is unsuitable because of the mould issue but tanked plasterboard doesn't have that, if say the reverse of the plasterboard is going mouldy then you have some serious issue that needs resolving. Somebody mentioned about pipes leaking, well that's just stupid, if you have leaking pipes then regardless of it being backer boards or PB you are going to have to some major work on your hands.
Personally I feel 12mm backer boards are more flexible than 12.5mm plasterboard, Say I was doing a wet room from scratch more than likely I would opt for 20mm backer boards. Not saying 12mm isn't right, it's just a personal preference to fit 20mm.
The fact manufacturers spend R&D money bringing out new boards doesn't make tanked PB 'unsuitable', if so then why would they develop tanking systems that you can use on PB??? Maybe like many you see paint on tanking systems as for the DIY market, personally I don't, I think they are a good product when used in the right situation. How many of us scoffed at the idea of lash clips? We all said it’s for amateurs, then when a few good pro's on here tested them out and gave them a good review some of us decided to give them the time of day.
In my mind... Are backer boards suitable in the OP's case... Yes, Is tanked PB also suitable... Yes.
I respect that you don't feel the same Deano but nothing you have said has made me change my mind or way of thinking... So far :lol:
