Usually, there is drywall under the wallpaper. It is not difficult to remove the wallpaper (by steaming, or another method) to get to the basic drywall. Then, you can texture it and then paint it.
I don't believe there is a drywall mud for use over wallpaper. As far as I know there is only regular , 'lite' and 'lo-dust' mud.
Answer
If you can remove the wallpaper first, that is preferable. For wallpaper that is solidly adhered, rough up the surface before applying the mud.
It is not advisable to put drywall mud over wallpaper backer. The reason is, the moisture in the drywall mud may cause the backing to loosen and this will result in your entire wall coating coming away.
It is possible to put drywall mud directly over wallpaper provided that the wallpaper is in excellent shape and is flat and well-maintained. If it is not, most wallpaper is very simple to remove.
Not a good idea, it will flake off eventually.
No, and you wouldn't achieve anything ! - Drywall mud is only for filling the seams not for clomping all over wallpaper. What a bizarre idea.
Kilz 2 will work under wallpaper as a primer and sealer over new drywall, drywall repairs, or other surfaces. If you are using it as a sizing for your wallpaper, it will work, but is not as good as using a real wallpaper sizing.
No, it will almost certainly loosen the wallpaper.
It shouldn't be a problem. The glue is water based and the mud should adhere to it.
Drywall, wallboard, wallpaper, wallflower, stonewall......
Drywall, wallboard, wallpaper, wallflower, stonewall......
I wouldn't .
No, but it does need some sort of finish. You can use wallpaper or a few other things without painting.
Use a sealer if the drywall was damaged while removing the wallpaper, then use a high quality latex paint in the sheen of your choice.
Yes, you can use Kilz over drywall. It is an undercoat, or primer.
Yes you can place a vinyl wallpaper over and over, but it will not be long lasting.
Replace the drywall with tile backer.
If it's on drywall, DON"T use sandpaper. Wet it all over with hot wet rag, let sit 10 minutes, then it will come off easily.