okay that was helpful.....
Youre right the thin stuff (and Im assuming you (and foodpump) are referring to common grade FRP panels)
wont work on a moderately uneven wall, (I've used it a lot and hate it a lot), as you need a perfectly flat wall to
glue it to, or you'll see waves galore.
Now, just because youre talking 8mm doesnt mean itll stay flat on a wonky wall, just depends on
how much flex this pvc stuff has, and how uneven the wall is.
If you can cinch it up with fasteners and it stays flat and rigid, problem solved.
If not, I see two practical choices here,
A) You run a long straight edge along the wall and mark the low spots, (and FP's plumb-bob method would be helpful too)
then glue shims to existing wall until its relatively flat at 24" intervals both horizontally and vertically.
Then glue up your panels and apply. And yes all purpose construction adhesive is the way, again as FP mentioned.
Its thick, cheap, and sticks to most anything. As to shims, the cardboard ones will work for a glued wall covering panel.
But dont use the construction adhesive to layer shims--its too thick. Use fast drying paper glue, contact cement, or etc.
B)You furr the wall with wood furr strips, making a "grid" with 24" centers.
With this method you have something more solid to attach to should you use fasteners rather than glue.
Things I'm still wondering:
1) Whats the current wall surface? plaster? Drywall? Ply?
2) Whats IN the walls? Wood studs? Galvy studs? Or other?
As to the domed celiing, do you really need a scrubbable surface up there? Something else might be more
decorative, small designer acoustic tiles or strips for example. Depends on the height and codes I suppose.