Tiling en-suite floor

[lewissv]

I was due to go on a course at Diamond tiling last weekend but it got cancelled.
I need to get on with my floor tiling though, so I have a question.
The floorboards I have in there are large squares of what looks like chipboard (but quite densley packed). They are screwed down and also appear to be glued in the joints.
The floor area is not very large and the boards seem very solid and stable.
Do I need to add a plyboard layer on top before I tile?
Also, why is it needed anyway? Is to make sure the floor has less movement in it?
I hear lots of talk about using plywood before tiling a floor - and screwing it down every 200mm. If its screwed down to the existing floor, then if that has some movement then the plyboard would as well wouldn't it?
1) What is the reason for the plyboard
2) Do I need to use it on a smal floor (2m sq max)

Thanks,

[Dave]

Hiya....i personally don't tile directly to chipboard as imo it is not stable enough to tile too..providing it is solid enough deflection wise i tend to use hardi 250(6mm) stuck with flexi cement addy and screwed down...

why was your course cancelled..?

[lewissv]

Thanks Dave,
I will try that. I don't want to go more than 6mm or the floor will end up too high.
They called last Friday to say the instructor was ill so it was cancelled. It was for the 5 day course, but done in 4 days over 2 weekends instead of during the week. They have booked me on the next one for July 4th.

[Dave]

Ok ..As long as you got a new date......