Hi,

I have plastered a room as best as I could

I hope to hang wallpaper but I am not sure whether I need to apply
something to the plaster first. I understand if painting the plaster
you should use a mist coat of either water or 50:50 water/emulsion but
I am unsure what the rules are when papering?

Can I just size it with watered-down wallpaper paste or should I use
50:50 water/emulsion as for painting?

In the past I have used 2.5L tubs of plaster primer but I noticed at
B&Q these are now quite expensive. (£10ish for 2.5L IIRC)

I have heard people say that B&Q value emulsion is very watery and no
use for painting with! I don't know how true that is, but I thought it
might do as a cheaper alternative for priming. I think the price is
about the same except you get 5L for your money rather than 2.5L. I
suppose that if you are diluting the paint, you actually get 10L for
the price of 2.5L of primer.

What does the group recommend?

TIA