Level tongue and groove in subfloor for gypsum board

[Dr Benz]

No one wants to give tips on the trowel size and type?
Saw a video where someone says 10mm trowel but someone else said it should be rounded for such large tiles and that 10 isn't enough…?

 

[Plupp 405730]

You need to double coat so the surface is even, then a 10mm notch works.

 

[Dr Benz]

You need to double-glue so the surface is even, then a 10mm trowel works.

Yes, double-gluing is included.
Ok, great.

Should one apply in the width direction compared to how they lay? So any air can escape at least on one side. Or does it not matter since the tiles are square?

Application, of course, in the same direction on the tile and the floor.

 

[BirgitS]

BKR has guidelines regarding the installation of large tiles here: https://www.bkr.se/regler/riktlinjer
It discusses two methods regarding spreading.

 

[Dr Benz]

BKR has guidelines for laying large tiles here: [link]
It mentions two methods for spreading.

That's thorough. Thanks, I have some reading to do while the rest of the floor sets.

 

[Bengt65]

Better to use floor leveling compound with a mesh...

Jumping into the thread a bit. We have a house from 1927, on the lower floor there's a hall with old parquet, smooth but ugly; there's a kitchen with parquet too, smooth but ugly. Then there's a dining room and a living room with the old boards exposed. Between these rooms there was a wall that's been gone since the 60s, we saw that on newspapers lying on the floor. There's a level difference between these. How do you know if the floor can support the leveling compound and can you determine that yourself? It's quite a few sqm, about 8x4 meters.
Grateful for tips and advice. You seem to know what you're talking about.