In remodelling a room, hanging wallpaper should be one of the last things you do. If you need to do any painting, do that first. It is much easier to get adhesive off a painted wall than it is to get paint off from wallpaper.
Remove light-switch covers, outlet covers and any wall hangings. Turn off electricity to switches and outlets to avoid electrical shock. You do not need to remove molding. Nevertheless, running the paper under woodwork makes doing the edges of your papering job easier and sometimes neater. Remove hooks, screws and anything else that might get in your way. Be sure to patch any holes in the wall. Papering over holes can cause strange-looking patches and makes the paper vulnerable to tearing.
You can hang wallpaper directly over painted surfaces, but glossy surfaces may not hold the adhesive as well as desired. To take out some of the gloss you can use a deglosser on the wall or simply scrub with a heavy detergent. Oil paint actually holds adhesive better than Latex. Before applying strippable paper, a coat of oil paint or an alkyd based paint is in order. Do not apply directly over unpainted wallboard, bubbling may result. At least prime the wall.
Papering over old wall paper is not a good idea. Inevitably, seams of the old paper will show through the new paper and dampness of the new paper may cause bubbling up of the old paper before the adhesive can dry. (Note that painting over old wall paper with any water-based paint is a mistake. The old wallpaper will flake off leaving an unsightly mottled appearance. If you must paint over wallpaper, an oil based paint is preferred.)
Removing old vinyl paper can be relatively easy. It involves merely starting a corner and pulling the pieces away in long strips. However, many older homes will have the old common type of wallpaper. Stripping then becomes a bit more laborious. To do this job you will have to root through your toolbox for a paper stripper, putty knife, and, if you have one, a wallpaper steamer. Actually a steamer is not necessary (although it is a handy tool). A bucket and a sponge or a spray-bottle will also serve to loosen up the paper after roughing it up. The process is fairly simple. Wet the paper and scrape it off with the scrapper or the putty knife. Where the water does not soak through put little gashes in the paper with a utility knife or paper scraper and sponge or spray the surface again.
If there are many layers of wallpaper on the wall. The best method may be not to scrape off the old layers, but to first tear off any loose pieces, then paint over with an oil-based primer. Use drywall mud to smooth over the rough spots, putting on mud and sanding off as needed. Then put another coat of primer over this.
To ensure that the wallpaper will stick properly on unprimed walls, you may want to use "wallpaper size" or some type of "resin sealer". If you are papering over wood, be sure to cover the wood with lining paper.
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