I disagree, firstly because it's not pistols at dawn but because he can see a debate going on and make his own mind up. I don't think anybody has advised him to keep the ply, so he can either either go down the route of tanked PB, backer boards or one of the other offerings in this thread. I'd say there is enough info on pros and cons in the thread to see what sits right with him.
I didn't realise this thread had started such a big debate! It was 3 pages at the last time I looked in and then it reached 5!
All good stuff though and you can't beat a bit of debate to put different ideas into a thread to help people make informed decisions.
I'll post some photos of the shower when we built it as soon as I have a chance so you can see. It seems the ply has to go which is not really what I wanted to hear as it involves the most disruption and "homework" time for me... I was hoping I could tank it or go over it with thin wedi, but it looks like they are both a bad idea. I haven't taken the tiles off yet but I am guessing the ply should be fine because that shower has never been used after finding out that it leaked.
If I remove the ply, can I cut it flush with the top of the tray and start with backer board from that point. (The ply goes down to the floor on all three walls, back, left and right, (below and behind the side of the tray), and it is screwed into the sole plate....) This last 2 inches or so of ply will need the tray out to be removed and the tray is probably siliconed down to the floor and side of the ply etc etc.... so it could be a pig to get out now.... If I cut the ply at the top of the tray then I would have a joint right where I don't want it, right around the entire tray.... Seems like a bad idea to me.
So does the tray have to come out too then start again from the floor up if I redo it with backer?
I'm still interested in anyone's thoughts on any way of tanking or lining the ply if possible and if it is in very good nick because this is definitely the fastest and simplest route. But if it's a no go then so be it.