Painting Wallpaper
If you have wallpaper and are worried about the condition of the wall underneath the wallpaper, you may prefer to paint over the existing paper. In some cases, painting over the existing wallpaper is the best choice as removing paper from walls that weren't 'sized' properly in the first place can damage the actual underlying plaster, wallboard or even the whole wall. Painting can also be a quick fix, especially when you are not in a position to redecorate properly, like for example when you live in rented accommodation. This is especially true if your landlord has chosen awful wallpaper, or even worse, several different types of awful wallpaper in the same room.
Old Houses
If the house is old, and already has several layers of wallpaper and paint on the wall, it may very well be more problematic to remove the wallpaper than to just paint it. If the house was built using lath and plaster, it sometimes seems that the paper is holding up the wall. If this is actually the case, removing the wallpaper can cause more problems than it solves. If you use modern steam or chemical methods to remove the wallpaper, you can damage the underlying plaster and find that you need to replaster the whole wall. Removing layers of wallpaper, layer by layer, by hand in the old-fashioned way is no joke. However, if the house is very old you might find some interesting styles of paper and other things of historical interest along the way.
Preparing The Wallpaper
Like most jobs around the house, proper preparation is the most important part of the job. To prepare the paper for painting you need to make sure that the paper is reasonably sound. If there are bits of paper peeling away from the wall, you will need either to repast them to the wall, or to remove all the loose paper. If the paper bubbles, you should burst the bubbles and cut away the paper to the wall, smoothing all the edges. Go over the paper joins with wallpaper paste and if you don't want the edges to show through the paint, you can sand them down to make them smooth. You may need to use filler, caulking or spackling paste to fill any flaws to make the wallpaper as smooth as possible before getting ready to paint. If the wallpaper is very textured you might even want to give the whole wall a thin coat of spackling to even out the pattern.
Painting The Wallpaper
Before painting with your chosen paint, first prime the wallpaper with an oil-based primer, to help seal the paper. This will help prevent the moisture in the paint from seeping through into the wallpaper causing it to come away from the wall. It will also help to even out any texture or pattern in the wallpaper, making it less visible. Once the primer is dry, you can then apply your paint.
You will need to use two coats of paint to get the best effect and if you are using a lighter paint, you might even need to use three coats to cover up very dark wallpaper. To cover up textured or heavily patterned wallpaper you may want to use textured paint, or use a patterned roller to get a textured effect.