First of all, it is advisable to remove the old layer of wallpaper or paint, as their adhesive capacity is already weak and they would not be able to hold the newly applied wallpaper permanently. This will therefore require a wallpaper release liquid, which should be applied as indicated on the package. Before applying this special liquid to the wall surface with a brush or roller, it is necessary to roughen and loosen the layers to be removed with a wire brush and sandpaper, so that the wallpaper remover can easily penetrate under it to loosen the old glue. Wallpapers soaked in liquid can be easily removed from top to bottom with a spatula. If there is a layer of dispersion paint on the selected area, which is already easily separated from the wall, it should also be scraped off.
The wall surfaces to be wallpapered must be cleaned of rust, soot and oily stains. If for this it is not necessary to peel off the plaster, then it is enough to isolate the wallpaper from the wallpaper with an insulating material or a layer of primer paint. If mold is discovered, the root cause itself must be eliminated, otherwise it will make our lives difficult as a recurring problem over and over again. In connection with this, it is worth seeking advice from a specialist and eliminating the discomfort even in time.
Then it is necessary to replace the cracks in the wall, to cover any holes, gaps and other damage. Then, finally, as the final step in preparation, primer material should be applied to the wall. This is because this layer will prevent the wall from absorbing water from the wallpaper glue, and thanks to this, the wallpaper will stick more massively.
After about 24 hours, when the foundation is completely dry, you can begin to lay the wallpaper itself. During the waiting period, it is possible to paint the ceiling of the room, if it was not planned to wallpaper it.
In addition to preparations, a lot also depends on the quality of the wallpaper and the glue selected for it, so it is worth purchasing them carefully, seeking the advice of a specialist. Of course, the condition of the walls will also greatly influence the final result, but their complete repair is already a longer and more expensive procedure.