Hi, I'm laying 30x30x11 marble tiles on an overlay ply floor. I've got 2 quick questions I'd appreciate your input on,.. 1) What size grout lines should I leave? I'm not sure if this differs with the tiling conditions? IE. heavy marble tiles on ply overlay! 2) I have unibond rapid set flexible adhesive and evostik flexible 'all tiles' grout. I've heard everyone in this forum talk of various BAL and dunlop adhesives/grouts that are so good (and that I've never seen or heard of before now!)... have I bought the wrong stuff?? And would you advise adding further flexible additives or is this not necessary? I really want to get this right and I'll take everything back and rebuy if I have to. Cheers in advance everyone.