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Why ply anyway? I would replace the current boards with P5 chipboard then use a decoupling membrane or thin foam-core tile backer with ‘flexible’ tile adhesive. Should end up around 22-27mm from the joist.
Dramatic_Hammer-
Cheers both (@Sheppz). I am only repeating what a terrazzo reseller told me, which no one else has been up for challenging, although they do sound a bit puzzled when I tell them.
Sub 27mm from joists is perfect, and would result in a 20mm step up from board to new floor which I am fine with (almost like the idea).
I'm toying with the idea of 18mm ply + 9 mm concrete board think. Will ask the builder what he would do normally and try and work out some sort of rational middle ground.
This sounds sensible: http://www.ultimatehandyman.co.uk/how-to/tiling/tiling-a-floor
chrisbmx116
18mm floorboards atm, with 8mm ply and 10mm tiles on top which felt fine, I’d be happy with 20mm step.
Previous plan:
Remove boards and add 2x 18mm ply + 20mm tiles + adhesive =40mm.
The two sheets of 18mm were recommended by one company who supply terrazzo and no one is willing/capable of any sense checking or alternative which is pretty frustrating.
My builder is great but he’s not used terrazzo before so understandably doesn’t want to deviate from recommended.
Looking at what Diespeker have 10mm tile wise, both genuine and faux (the later requiring less floor build up).
I think EC used single 18mm ply for downstairs porcelain tiles.