You can definitely paint over wallpaper, but I have mixed feelings about it. First, the seams will show through the paint unless you carefully coat them with a skim coat of joint compound to hide them. Second, you must use an oil based primer to seal the paper, or the latex paint could cause the wallpaper paste to soften, causing the paper to "bubble". Another "hidden" problem is that many wallpapers have a texture... sometimes not very noticeable until painted. Flowers, anyone?
Even if the paper is vinyl (which generally does not let water through) it is wise to prime because using a good oil-based primer-sealer will insure that the paint will stick to smooth vinyl surface.
The reason I don't suggest painting over wallpaper is that if the wallpaper begins to fail, the walls will begin to look very ragged. The repair is not difficult… simply cut out all the loose areas and smooth them with joint compound. Since wallpaper failure tends to be progressive, this process of failure/repair will continue on and on over the years. If you spend the time now to strip the paper, you save yourself future disappointment.
Once you paint wallpaper, the removal process becomes much more tedious and difficult, since the paint has removed any porosity in the paper and also stiffens it by adding more thickness to the wall. The more coats of paint, the worse it gets!
Most wall coverings can be removed from walls, by a trained professional, with little difficulty. We spray the surface with a mixture of hot water and an enzyme based wallpaper remover. The enzyme breaks down the starch in the adhesive, and allows the old paper to be scraped off. A steamer is used on certain types of wallpaper to break down the adhesive. Whether wet stripping or dry stripping wall coverings, we always wash paste from the walls, with TSP.
After stripping the wallpaper and washing the walls of adhesive, we then prime the walls and check for rough spots (signs the adhesive is still present), before we paint. Once the rough spots are sanded down your walls are ready for your paint of choice.
Call Spectrum Painting for a free consultation about wallpaper stripping, wall preparation and painting! 850-529-0836