Refitting Bathroom Tile on top of Existing Tiles Query Advice and information on tiling and fixing tiles to a variety of surfaces

[Sophie'smum]

We are refitting our bathroom. This was part of a 1982 loft conversion. The walls are 4 x 2 stud work with plasterboard which has been skimmed. The original 8"x 6" 4mm tiles are stuck fast, sound & level. Sorry about mixing imperial and metric.

We intend to create a shower cubicle (presently an electric one over the bath) We have chosen but not yet ordered a 600 x 200 10mm tile.
I have found an old post regarding the weight bearing of skimmed p'board as 38k sq m. I have a sample of a tile of that size/weight and it is 1775g.

At 8.3 tile to the sqm = 14.75k I believe we are within the tolerance even though the weight per sqm of the old tiles & new adhesive is not known.

Believe me if the old tiles came off the walls would come with them. We would appreciate input that I am OK with my calculations and also the best way to prepare the walls, there has not been a shower there before and the grout is not epoxy. If we need to "tank" what exactly is that?

Also which adhesive to use? Should the whole tile be buttered? I assume as the old tiles are non porous then it is best done in stages to allow to dry properly?

We intend to place a moulding around the base of the walls, as in skirting board, but UPVC, There is very little wall that would need this due to shower tray, bath, vanity unit etc. Should we tile and then place the skirting over (my feeling) or skirting first & then tile? We are very lucky in not have much in the way of un-eveness anywhere.

Thank you.

[Sophie'smum]

As a postscript, not one person has posted a reply. Contrary to all that I had researched the weight bearing of plasterboard is reduced to 20k if skimmed (it is) and further if already tiled, clearly is. There fore my plasterboard walls would no way hold a further layer of tiles as large as these. So its all come down & new hardie backer installed direct to studding. Weight bearing 100k sq m & impervious to moisture as well. Hope no-one took all the info I first put up as being gospel. I was hoping for experienced people to put me right but hey got there in the end by consulting the buildign regs & tilers organisations.