As with any redecoration project, correct preparation of surfaces is very important for a good result. Walls must be clean and dry. All cracks and holes must be filled and smoothed down with sandpaper. Before hanging wallpaper on an absorbent wall (cleaned plaster, new drywall etc.), the walls should be sized with wallpaper size, applied with brush or roller. If a glossy paint finish is to be covered, the surface must be thoroughly rubbed with sandpaper to provide a 'gripping' surface. If you are papering over a dark painted surface or a patchy wall it’s preferable to apply a coat of white water-based primer.