Before hanging new wallpaper or applying paint, it is important that the wall you are working on is as smooth as possible. If you can feel a mark on the wall, it is likely that you will be able to see it through the new wallpaper. To make it smooth, use a scraper and 120-grit sandpaper.
Step 1 – Use scraper
Very gently and lightly use the scraper to smooth down the surface of the wall. After scraping, rub your hand over the wall to check that you have eliminated any bumps or higher spots on the surface.
Step 2 – Use sandpaper
Use your sandpaper to smooth the wall, checking the surface as you go. Take your time, making sure you feel the wall as you move across it.