I have to lay 18 sq m of 400 x400 ceramic tiles on a kitchen floor. The floor is roughly half concrete screed and half tongue and groove timber. The two sections of floor are level with eachother. Is it best to sheet the whole lot with ply? For the concrete section do I just drill the floor and screw the sheeting down at 300 centres the same as on the tongue and groove section? Advice would br appreciated.

i would use flexi adhesive and 6 mm hardibacker boards screwed down at 300mm centres instead of ply much better to tile on with no chance of failure like ply, and wont give you height issues 15mm min for ply!

Originally Posted by snuggles1

I have to lay 18 sq m of 400 x400 ceramic tiles on a kitchen floor. The floor is roughly half concrete screed and half tongue and groove timber. The two sections of floor are level with eachother. Is it best to sheet the whole lot with ply? For the concrete section do I just drill the floor and screw the sheeting down at 300 centres the same as on the tongue and groove section? Advice would br appreciated.

If you choose to oversheet the area with cement board you fix with adhesive over full are but, you only need to screw into timber substrate. The adhesive will be sufficient enough to bond the cement board to the concrete on its own.

if budget permits you could over sheet the area with an uncupling membrane or place an expansion joint over where the to different substrates meet.

The biggest risk with substrates like this is that one substrate will deform more than the other. Tongue and groove floorboards expand and contract more than most other substrate. Wood expands most across the grain so for every plank over the joists there will be a little expansion even when planks are nailed and screwed the wood still expands.

Yopu can never garuantee to prevent failure due to expansion etc so you just try your best to eliminate it and I feel that over sheeting with a backer board is the minimum and first step in your case.

good luck, let us know how you get on.

How thick is your tongue and groove? and are you having any under floor heating?

Thanks to all for your advice. Will go with the glue and screw method for the whole area. Fingers crossed!!