I need information about the material behind the wallpaper above the fireplace. I am removing wallpaper from a room and when I got to the wall paper above the fireplace, there was a brown colored layer that is no where else in the room. Anyone have an idea about what that may be. I was thinking it was some sort of barrier from the fireplace chimney and the wallpaper but I am not sure. If it is how do I replace that barrier?