Tiling on floorboards

I'm about to tile a kitchen floor with 250mm x 400mm tiles and am wondering what the minimum thickness of hardboard i should lay on top of the floorboards. I know i have to put something on top of the floorboards as laying tiles directly won't be a good idea but i don't have room for 18mm ply as this will be too high. What is the minimum recommended thickness of ply to use over the floorboards so that the tiles and grout won't crack. thanks

The minimum recommended is 12mm, I have previously removed tiles that were laid on just 6mm ply (I wouldn't recommend this) but the floorboards beneath were in very good condition and were flat and solid.

Whats preventing you from raising the floor?

The other option you have is to remove the floorboards and lay 25mm WPB chipboard, which you can tile directly onto. Thus you shouldn't have a problem with the floor raising too much.

Gob's

Thanks Gobo, Tiles are going into another room and then stopping so am just trying to prevent too much of a lip.

https://www.pureadhesion.co.uk/stor...HardiBacker_250_Installation_Instructions.pdf

6mm backerboards.