How do I paint over wallpaper?
You will first have to pull off any areas that are easily removed like edges that lifted and seams that have curled up.
Using a latex primer can often result in a bigger mess as the water in the paint starts to lift the paper wherever it is poorly bonded. Use an oil base primer like KILZ as it bonds very well to the wallpaper face and does not cause any of the spot lifting. Kilz comes ready mixed and is a very thick coating so I suggest you reduce it about 20% with paint thinner. This allows you to spread it easier and more evenly.
Allow the primer to dry and remove any small areas of the wallpaper that may have curled up. Spackle any seams that are showing, rough areas left from removing efforts and other imperfections. When dry sand lightly with 120 grit sandpaper, spotprime those areas and proceed with your new finish, new wallpaper or a coat of finish paint.
Hope that helps!
You can also use a product like Zinsser's BIN Primer Sealer to promote a sound adhesion to the wallpaper whether it is vinyl, paper, or grasscloth. The downside of BIN is the alcohol fumes from the white pigmented shellac and the limited window in which to topcoat to get the best adhesion between coatings. I prefer to prime with BIN around an hour before adding a flat or eggshell coat of paint. I have seen more elasticity in satin and semi-gloss enamels that have caused bubbles to form under the wallpaper. The BIN will help the coating slightly more though than using an oil primer or an acrylic.
But otherwise "prkswllflwr" sounds pretty experienced with this process and I agree with her answer.