I've created many threads now as we are doing a total renovation of our kitchen in the house from 1913, but I'm trying to spread them in the right forums to get the most/best answers 
Now it's about gypsum.
In other rooms we've renovated, we've used rep-gips which is 6mm thick because these boards follow the unevenness in the old walls that are quite crooked and wavy, and we haven't wanted to hide this as it's an old house, and it feels perfectly fine that everything isn't perfectly straight.
But in the kitchen, we've planned to use regular gypsum, 12mm, to make it a bit less uneven, as it makes it easier when installing the kitchen frames (Ikea), which you want to be as straight as possible.
Because if I understand correctly, a 12mm gypsum board doesn't follow the wall's irregularities like a 6mm one does, and you do put gypsum even behind where the kitchen frames are to be mounted, right?
But then there's the question, when screwing in the rails for the cabinet frames, is there a risk of cracking the gypsum when there might be some air pockets between the wooden wall and the gypsum?
The walls, by the way, are horizontal boards with wood fiber insulation behind.
Now it's about gypsum.
In other rooms we've renovated, we've used rep-gips which is 6mm thick because these boards follow the unevenness in the old walls that are quite crooked and wavy, and we haven't wanted to hide this as it's an old house, and it feels perfectly fine that everything isn't perfectly straight.
But in the kitchen, we've planned to use regular gypsum, 12mm, to make it a bit less uneven, as it makes it easier when installing the kitchen frames (Ikea), which you want to be as straight as possible.
Because if I understand correctly, a 12mm gypsum board doesn't follow the wall's irregularities like a 6mm one does, and you do put gypsum even behind where the kitchen frames are to be mounted, right?
But then there's the question, when screwing in the rails for the cabinet frames, is there a risk of cracking the gypsum when there might be some air pockets between the wooden wall and the gypsum?
The walls, by the way, are horizontal boards with wood fiber insulation behind.
Make sure you have absolutely silent where you are going to screw!
When the screw you're using to secure the board sinks through, it's not solid behind; you can feel it flex with your thumb. The board gives way when you screw in and releases the head when it springs back. How do I know?
I have a setup to test every 30cm with a straightedge where the screws will go, to ensure the wall is reasonably straight. Then shim where there's too much space before the drywall goes on.
I'm also planning to build a bracket to space out the rail for the middle part of a U-shaped kitchen for a 70cm countertop, and that way you get it straight for the entire rail.
I have a setup to test every 30cm with a straightedge where the screws will go, to ensure the wall is reasonably straight. Then shim where there's too much space before the drywall goes on.
I'm also planning to build a bracket to space out the rail for the middle part of a U-shaped kitchen for a 70cm countertop, and that way you get it straight for the entire rail.