This is a question that many homeowners ask after finding out exactly what is required to remove old wallpaper. From the mess it makes to the damage it can do to the wall underneath, you probably want to hear that you can remove the old paper without any kind of qualification.
The truthful answer is that it really depends on a number of factors.
The State of the Current Wallpaper
Unfortunately, the state of the current wallpaper plays a large role in whether you can wallpaper over it or not. If the old wallpaper is cracked, peeling, or seriously damaged, hanging new wallpaper will exacerbate the problem. Not only will it reveal the problems and state of the underlying wallpaper, it will increase the chances that your new wallpaper will start to peel faster (especially if the wallpaper is old and falling off of the walls already).
The Existing Wallpaper’s Material
A safe way to determine if your new wallpaper can be applied over the old paper is to see if you can tell what kind of wallpaper is currently on the wall. The only wallpaper that is nearly guaranteed not to cause you residual problems if you leave it on the walls is non-coated wallpapers.
While researching your current wallpaper would likely be a very time consuming endeavor, you can save yourself the time by testing it.
1. Use a wet sponge (wet, not just damp) and rub it against an inconspicuous part of the wall.
2. Check it to see if the wallpaper gets dark.
If the wallpaper does get dark, it does not have a vinyl coat. If it has a vinyl coating, you really need to remove it before hanging your new wallpaper.
Current Pattern and Color
Even if the wallpaper is in great shape and does not have a vinyl coat, you may not be able to leave it hanging. If the old wallpaper has a very dark pattern or color, you probably won’t be able to leave it on the wall, especially if you are switching to something a bit quieter and lighter in color.
The best way to test this is to hold your new purchase up against the current wallpaper and have someone stand a good distance from it. That person can analyze it to see if the old wallpaper is visible. There are a couple of issues with this though. Holding it up against the old wallpaper is not the same as actually hanging it. It is possible that the pattern or color only shows up after the application is done. If you have any doubt about the old wallpaper showing through, it is best to take it down before you create a very strange visual effect with the old and new wallpapers.