We have plaster under layers of paint. The first layer is peeling in spots on our living room walls. My husband tried to sand with 40 grit sand paper and it didn't budge. He used a scraper and got halfway through the job and now the paint became very difficult to remove. Now we have half the room with smooth walls and half with the peeling surface that won't scrap off so if we try to sand it and then paint the one side of the room will have a different texture. What do you suggest? Thank you.