Painting over wallpaper is usually not suggested because the wallpaper may end up coming loose from the wall at a later time.
In most situations, you should remove the wallpaper before painting.
If you have a situation in which painting over wallpaper is desired, follow the instructions below to paint over wallpaper properly.
Make sure your wallpaper is glued to your wall very well.
If your wallpaper has bubbles or edges that are coming up, do not paint over it - remove it before painting.
If you only have a few edges coming up a little, then proceed to the next step.
Repair Edges and Seams
Remove any of the wallpaper edges or seams that are coming up.
Sand your wall and wallpaper very well in these areas to minimize the transition between the wall and wallpaper.
Clean the wall with a damp towel to remove all the dust.
Paint your wall with a quality primer, such as Zinsser, Kilz, or Zap, and let dry.
You can have your primer tinted to be close to the color of your paint if you wish.
Check and Prime Again
After the primer has dried, check your wallpaper's seams again to make sure that they still are stuck well to your wall.
If the wall is not as smooth as you like, sand the wallpaper seams again and make sure the wallpaper is free of dust.
Use paint primer again on those areas and let dry.
Texture your walls to help make the wall's imperfections less noticeable.
You can add texture to your paint or primer before painting, apply a spray texture from a spray gun or in a spray can, or texture using a brush and texturing material.
Materials used to create texture soak up a lot of paint, so you will probably want to use primer on the walls again before painting.
Now that your walls are properly prepared, you can paint your walls as usual.