Thanks for the advice.
I got Zinsser 123 Bullseye and after only one coat it's dried without any sign of the pattern coming through.
Seems to have done the trick brilliantly.
Cheers
Hi All - new member here.
Was painting over what appeared to be a old plastered wall which was pretty smooth. However as the paint has dried the pattern of a raised wallpaper has started to come through which was never visible before.
I reckon it must be a thin coat of plaster has been...