Water proofing shower cubicle

cyclonebri1

Taking this back further than where it started as the walls have already been plastered so is no use to the op but might help someone else, this is what I've done in a refurb with a new bathroom extension;

I didn't plaster the walls where the shower would be installed, a corner over the bath.
Used tilebacker or no more ply, can't remember which.
This was bonded to the wall with the recommended adhesive, and screwed back using phosphate/ceramic coated screws intended for the job.
Then sealed the gaps again with the proper sealant.
I boarded to floor level and under the bath as I was also tiling all the floor.
Ok, maybe I was being a little anal with all the screws in the wall, but KNOW it's been done right.