McP77

On a technical level I sort of agree with the above as reading British Standards it doesn't explicitly state that a domestic shower has to be tanked. But it does state that plaster is not a suitable substrate for tiling onto in wet areas. I also believe that a domestic shower is one that is used for less than 10 minutes per day. A couple of people using a bathroom will probably be in there longer than that on a daily basis.

On a personal level I include tanking in the quotation, state that it is being done and don't give them the option to not have it. Starting a job in a couple of weeks time where previous tiler didn't tank and the tiles are now falling off. Customer really p***ed that tanking was never mentioned to him and thinks tiler is an idiot for not doing it.

Not sure what to advise you in your situation as I don't want you to push tanking and end up losing the job but after seeing a demo of water penetrating water resistant grout and adhesive the plaster can get wet.