I wish to paint my hallway with plain matt paint. However, I stripped of the old torn wallpaper some of the under layers of different paint levels came away with the paper. As a result, I have very uneven and bumpy walls. For example, there are patches of grey bare plaster, patches of this colour of paint and patches of another colour of paint, etc. I have tried sanding down the edges of the paint patches - but it doesn't seem to work because when i apply new paint it still looks uneven and bumpy Can anyone please advise me what to do?