John Wale
Chances are the plaster will crumble whatever you do. I recommend you use a product called Dif. Available from Brewers. Score the paper first with a blade or use what is called a paper tiger. Again Brewers will help with this. It creates holes in the paper, then the water and Dif will penetrate better. The old saying is ‘let the water do the work’. Meaning let it soak. Re soak and soak again. Don’t spend time having to scrape hard.
