hi guys, thanks for your comments. it would be almost impossible tpremove the existing ceramic tiles. i am in spain and tiling both floor and walls of a bathroom. the existing tiles are tiled onto floor, a concrete sub base and walls, spanish bricks which are pretty fragile. both the bathrooms in my own house have been successfully tiled over with porcelin tiles with a grout line. this is for a friends house who would like it without the line and i advised her against this.
i just wanted to get some professional advice so that i could tell her for sure not to go ahead without the grout line.
thanks guys for reafirming my advice. you have all been very helpfull