Rockwool slabs for 4x2 CLS

[noseall]

Extra plasterboard will help though. 2 layers of standard PB will trump a single layer of the acoustic stuff.

Agree. Especially if the joints are bonded/staggered.

 

[Deluks]

It is highly unlikely to get Rockwool to compress 11mm in unison whilst trying to individually screw. You will end up with a lot of popped fixings and a piece of plasterboard thrown across the room.

I've managed to compress 30mm RWA45 down to 25mm successfully, but I was using 15mm plasterboard.

 

[noseall]

I've managed to compress 30mm RWA45 down to 25mm successfully, but I was using 15mm plasterboard.

I reckon a slab of Rockwool, with a sheet on top of it, could support a lot of weight, without giving much.

 

[Deluks]

I reckon a slab of Rockwool, with a sheet on top of it, could support a lot of weight, without giving much.

You can concrete directly over the top of it if you have the right grade, but consider that it varies from 45kg to 140kg per cubic metre, you need to make sure you've got the right one for your spec.
It's a shame that rockwool product names are so confusing, the marketing guys need to give the technical guys a slap, they have too many options.