I am in the process of remodeling my bathroom. Today I removed a tacky wallpaper border the previous owner had installed and discovered under it chipping paint. I've never dealt with chipping paint before, I've been told to sand down the area and primer it. What confuses me, is while I was removing the wallpaper, I noticed a brown almost cardboard like material was exposed where the paint had chipped off. When I would spray the area with water (to loosen up the wallpapers adhesive) this cardboard like material easily came off and exposed a light brown board. There is so much chipping I don't know if sanding the area would even look good? Should I chip off the remaining paint and remove this cardboard like material and then primer that area? The picture I have attached is an area where I removed the chipping paint and the cardboard like material... Any guidance would be great.