Hey Everyone! I am just starting to redo my bathroom in my 1950's home. I am a complete novice when it comes to DIY. I just took the wallpaper down so I can paint. Unfortunately, there is not a smooth surface underneath. I also have some crumbling drywall. I'm really not sure if it's drywall or plaster. The top half is blue and rough. What I would like to know is do I need to have this stuff drywalled? What preparation do I need to do before painting? Is there a type of primer that would give me a smooth surface? Thanks!