Thickness of ply for floor tiling

I would use 9mm in that circumstance, and appropriate tile glue for non solid floors.

Recommend you look at the BAL web site...

http://194.223.92.131/pdf/Technical%20Data%20Sheets/B%20&%20C%20Technical%20Data%20Sheets/BAL_Supercover_Rapidset.pdf This is an example data sheet - find the right one for your tile/adhesive combination. Top right of second page gives details for floor covering prior to tiling when using this particular adhesive.

If in doubt ring BAL for recommendation.

No financial interest in BAL but have been impressed with their products in the past.

Phil

My bathroom installers used 12mm on an upstairs bathroom floor with definite bounce. (It's a good thing the ceiling below is old hairy lime plaster).

So I would have thought 9mm on a firm floor would be enough.

Dont even think about using plywood. I used to use it, but would'nt consider it now, just go to Topps, or any decent tile supplier, or even builders merchant, and get some Hardiebacker board. Dead easy to cut to size, only 6mm thick, and as stiff as 15mm plywood.

I've always used 12mm on bathroom floors, with no comebacks. Unlike a bloke I know who had his bathroom floor tiled (by some fecking cowboy) straight on to the chipboard in a modern thrown-up house. Within three or four years the floor was ruined, with tiles cracked like eggshells and lifting up.