Simple floor raising for new tile layer

[UnluckyChris]

This is a really simple one I'm sure. I searched but didn't find a specific answer which probably means I'm being thick!

I removed the old tiles from my kitchen floor, down to a concrete layer. Now I have a difference in floor height between the kitchen and the lounge area - about 25mm (there was at least two layers of old flooring that came out). The tiles I'm going to put on are about 8mm porcelain, I guess (I've never tiled before) the grout layer will be about 3-5mm, which leaves me with a 12 mm gap so I need to raise the floor.

Originally I was going to use self leveling compound but I decided the floors pretty level, so I guess I need to put a plywood layer down? Is this the correct approach?

Assuming that it is, how do I attach the plywood to the floor - glue? Do I even need to? Also do I need waterproof ply, or do I treat the panels before they go down? Is waterproof ply going to be easy to find in a shop? Finally is my estimate of 3-5mm grout layer to fix the tiles about right?

Thanks,
- Chris.

[marc1106]

When you lay the adhesive(not grout) on the floor using a half inch halfmoon trowel (nice and thick) then lay the 8mm tiles onto that 13+8=21mm so just build up the addy by a few mm and your in the ballpark!

[marc1106]

ps if they ARE porc tiles then i hope youve invested in a decent cutter!