How to fit Kitchen floor - part plywood part concrete

[grcj8]

Hi,

I have a kitchen that is 3/4 part floorboards and 1/4 concrete. and want to put ceramic tiles down. The floorboards were around 22mm thick and there is a slight slope away on the concrete end of the floor (concrete area is around 2 x 1m in total)

I have taken the floorboards up and purchased some 25mm WBP plywood and currently in the process of putting noggins down in between joists where the edges of the plywood will go.

The next step I believe is to prime the underside and edges of the plywood and screw to joists and noggins once this has been cut to size.

However am struggling to fully understand how to deal with the concrete area. My thoughts were that if the floorboards were 22mm and I put 25mm plywood down then I would need to use some levelling compound to fil in the area of the concrete so that it brings it up to the plywood level and in the same processing resolving the slope. Is this correct? and what product should I use for this?

Also what product do I need to use to fill in any gaps to stop the levelling compound from just flooding to other areas? and will I be able to use it when increasing the level by 3 - 4cm to bring it up to the floorboards?

I take it once that is done I just need to use a flexible adhesive, lay tiles and grout?

 

[foxhole]

Run the ply over both timber and concrete, screwing and gluing in place then you have a level floor to tile.

 

[grcj8]

I can't put ply over the concrete though as there is only a 3mm gap between the top of the 25mm thick plywood and the concrete base