how thick can you reasonably skim a drywall finish?

[SparkyTris]

I have just ripped off a tired old internal wall.
The composition of the old wall is/was:
studwork: 12mm plasterboard : 12mm plasterboard : 4.5mm faced ply

the only reason it came off was that the faced ply "trawler-wall" was deemed aesthetically displeasing.

I have discovered that I can remove the faced ply and the top layer of plasterboard without substantially affecting the lower layer of plasterboard.

2 questions:

1 - can you get 12+4.5 = 16.5mm plasterboard?

2 - if not, then I know I can get 12mm plasterboard, so what is the easiest way of bringing the surface out another 4.5mm? is it reasonable to ask for a skim to get out to that?

I want to come out to the original level as close as poss so that I don't have to muck around too much on the nosings for doors etc.

 

[Bonni]

You can buy 15mm plasterboard.

If the plasterboard is to go onto stud work, do you just not put the nessecary thickness packers on first before the 12.5mm plasterboard?

 

[23vc]

Once skimmed 12.5mm plasterboard will be 15.5 so you’re within 1mm ie not an issue ? Sounds like a complete non issue unless I’ve misunderstood