How to wallpaper over old wallpaper?

It is not recommended to apply new wallpaper over old wallpaper. Doing so could cause bubbling in the underlying wallpaper and old patterns showing through your new paper. It’s best to remove old wallpaper before applying new wallpaper especially when dealing with non-breathable vinyl-coated papers which could result in mould and mildew build up between the layers. Even the most stubborn wallpaper can be removed with the proper wallpaper removal solution, perforations tools, and some hard work.