Wall preparation before plastering + painting

I have a room that was plastered at least 9 months ago (probably quite a bit longer - it was like this when we bought this place) which is still bare plaster and we're planning on putting lining paper up before painting. Sadly the quality of the plaster work isn't great (its nice and smooth in places, but there's ripples/bumps in other places, and not to mention a small but noticable crack (which we'd like to paper over). We may well just paint the better walls - but we'll just have to see. Its a nice and easy room to line - which should give us some practice for our other room we need to line.
Based on this - what preparation should I do before pasting/painting? I've got 6L of Screwfix PVA bond which I think on the back says it can be diluted 4:1 to seal things like this. Is this okay, or could I dilute it a little more? Is there something better to put on before papering/painting?
Also - I've got a large area of plaster missing from a wall (it had all blown from the blockwork) and I think I may need to put PVA onto this wall as well before replastering (else all the water would be drawn out). Should I just use the same dilution as I do on the other wall?
Thanks
D
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David Hearn wrote:

Yup, 4:1 PVA is exactly what you need. Use it liberally, and apply to anything that looks remotely crumbly or porous.

Yup, as above.
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