What a wealth of information! Much appreciated knowledge on here and now posting my first questions. Never heard the one about the "erudite" tiler and his reaction to gypsum.
I AM the minion, a heating engineer and plumber, sometime ceramic tiler and now met my match in these 600x600 and 600x300 porcelain tiles for my mate's bathroom.
Looks like I might have to strip existing ceramics but wonder if I have to plasterboard or could I prime and fix direct to the brickwork and concrete block walls? I'm expecting to use quite a deep adhesive bed and that might take care of surface irregularity.
Is fixing direct to the brick a stronger job?
Largest single area is 2.4H x 2.4W ie. 4 tiles high x 8 tiles wide, obviously don't want them to come off but it's not quite the same scale as a hotel lobby etc. so I'm thinking we might be able to do a professional cheat and still achieve a good job.
Insulted? Aghast? or able to offer support? Comment please, cheers, Geoff

in that situation i would always dot and dab plasterboard the wall, the reasons are .

. Your brick wall, will not be a true flat surface and there is a good chance, even with a deep bed trowel that your tiles will either sink or lip in places, especially if you are planning to tile brick bond style.

. dot and dabbing, should be plumb and flat, you will not need to worry about adding extra adhesive in low spots,

. the plaster board wont cost too much and in the end it will save you time and effort, you should be fine with those tiles, but just check on the box that they do not exeed 32kg per m2

as rav has said dot and dabbing is the way to go a nice flat level surface it will save alot of hassel always remeber prep work is the key factor to any tiling job

You may be better using a tile backer board instead of plaster board these will normally carry around 50kg per mt2 against the 32kg of plaster board just in case you are struggling with weight on the wall