While it is possible to paint over wallpaper, it is generally better to remove it first to guarantee a smooth, professional finish. Painting over wallpaper can save time, but it may lead to issues if not done correctly.
You can paint over existing wallpaper if it is in excellent condition: smooth, non-textured, clean, and firmly adhered to the wall. Ensure there are no bumps, tears, or peeling areas, and that all corners and seams are securely glued down. You might also consider painting over wallpaper if removing it would damage the underlying wall. Additionally, some wallpapers are specifically designed to be paintable, which can add texture to a room.
However, there are risks. If the wallpaper is textured, damaged, or peeling, these imperfections will show through the new paint. The moisture from the paint can also loosen the wallpaper's adhesive, causing it to bubble and potentially damage the wall. To mitigate these issues, clean the surface thoroughly and use an oil-based primer to help the paint adhere and prevent the old adhesive from bleeding through.