Hi there,
A few years ago, I would have answered this question easily without second thought, however all attempts at using the normal sizing advice have failed.
The plaster is likely 30 years old and is as dry as a bone. I have decorated it myself both with and without sizing, and the paper has basically fallen off within about a year. It has also been done professionally and still the paper just falls off.
So has anyone got any really hardcore methods of getting this plaster to be receptive to wall papering!?
Many thanks