Tiling on Chipboard

[newdud]

Hello
I am about to start to re do the up stairs bathroom. As part of the re-model I will want to put down floor tiles.
The floor is standard chipboard, I know that it would be a bad idea to tile directly on to the chipboard so I will be putting down 9mm ply wood on top to strengthen the floor.
My question is how do I stick the ply to the chipboard. Do I use glue or glue and screw it down. If using screw do I screw to the floor joist ?
if using glue, what type of glue ?
Can some provide some advice on this.
I have done some research on the interweb and each web site seems to offer a different advice
Thanks

[whitebeam]

I would'nt be using 9mm ply either, if your floor has no bounce then I would use 6mm hardie backer....

A single part flexible to stick, then screw.

[newdud]

Thanks for the quick reply.
The will floor will have some bounce, I will know more once I have removed the bath etc.
I am concerned about the height as this will raise the floor by quite a bit once the tiles are taken into account.
Can you recommend a glue and screw type

[Sir Ramic]

Then remove old floor, strengthen joists and use 18mm ply or thicker. Over board with 6mm backer board....jobs a goodun !

[whitebeam]

If the floor has bounce, that must be sorted first otherwise a failure will accure..

A single part flexible adhesive I use a notched trowel of 7mm and screwed with Screwfix turbo gold screws, 25mm so i don't protude the existing boards/floor in case of hidden pipes etc

[tfs]

An increase in height can be small price to pay for peice of mind!

Doors can be trimed to fit and door bars can be made to act as a reducer transition between rooms. Only time its usuauly a big issue is in kitchens when appliances need to fit under worktops or if plumbing wont permit in bathrooms.

[newdud]

Thank you every one who have contributed.
Once I have removed the old bath / toilet etc I will make a decision on how to proceed, now that I have some idea what to do