The Nuts and Bolts of Wallpapering
Every wallpaper label probably states some version of the following: “The wall surface must be clean, dry, hard, smooth and slightly absorbent. Old wallpaper and non-adherent layers of paint must be removed and any unevenness evened out.” Some people, however, do not take these recommendations seriously. Yet wallpapering can be so easy if wall surface and wallpaper type are suited to each other, and if some basic rules and tips are observed.
Removing Old Wallpaper
Before wallpapering, any old layers of wallpaper must always be removed. By hand, this can be done with a ceiling brush, water, stripping solution and a paint scraper.
Stubborn old wallpaper that cannot be removed despite wetting it several times can be perforated with a spike roller. Washable and scrubbable wallpaper can be more easily removed in this manner. However, if the wallpaper was glued using an adhesive dispersion, the only thing that will help is using a steam wallpaper stripping machine to steam off the old paper. In the case of old, peelable wallpaper, the residual substrate could theoretically be left on the wall to serve as lining paper. However, in practice, this rarely works. Bubbles often form when the new wallpaper is applied to it. It is definitely better to completely remove the old substrate.
Layers of old, non-sustainable or cracked paint or finish must be removed before wallpapering. If this cannot be accomplished with simple sanding, paint strippers will be required.
Wall surfaces of the mortar classes PI to PIII, which include fresh lime and lime-cement mortar, among others, are highly alkaline and should be neutralised before wallpaper is hung. The most common method is to use a fluosilicate solution, which transforms the base calcium hydroxide into an insoluble calcium fluoride, thereby neutralising the plaster surface. This reaction also effectively seals water spots.
Smoothing and Flattening
Wall surfaces in new buildings are generally ready to wallpaper. However, you should not simply rely on this fact. Often there are small flaws that can be evened out with a filler, discolourations that must first be sealed with a sealant, or a variety of absorbent plaster types that need to be evened out.In the living area of both old and new buildings, one will primarily find three different smooth wall or plaster types: gypsum, beige-coloured lime finish, and gypsum plaster board. While fillers containing gypsum can be applied directly to gypsum and gypsum plasterboard surfaces, these fillers cannot be used on plasters containing lime and cement, such as a lime finish. For alkaline interior plaster, special fillers, e.g. a dispersion filler, must be used.
Believing hat wallpaper can disguise flaws in the underlying surface is a myth. Perhaps voluminous textured or fabric wall coverings can, in some situations, hide small unevennesses. But in glancing light, poorly plastered seams on drywall boards show up as clearly as blemishes and ripples in plaster.Uneven, rough wall and ceiling surfaces are best smoothed out by plastering the entire surface. Specialty stores stock joint compound specific to this purpose, which can be efficiently applied and thinned out to nearly nothing. These products are applied with a smoothing trowel and, with the help of a long aluminium scraper, skimmed off over a large surface in a single motion. After the plastering is finished, any ridges are scraped away with a wall and ceiling scraper. Finally, the surface is sanded and the dust is removed. Large surfaces such as ceilings can be particularly efficiently treated with a so-called “sanding giraffe”. This is a mechanical circular sander with a large sanding plate and a long handle.
The choice of the correct primer material depends entirely on the type and properties of the underlying surface. Primers can alleviate a too-strong absorption, stabilize mildly sandy or chalky paintwork, even out colour differences or prevent softening of the paper on drywall boards.
Diluted hydrosol penetrating primer stabilizes mildly sandy or chalky substrates. A white pigmented wallpaper primer evens out colour differences in the underlying surface. This is used primarily under thin, translucent wallpapers. Wallpaper-changing primer finds its greatest use on surfaces that will be frequently re-papered, such as in store construction, rental housing, and on tradeshow furnishings. A separating emulsion of this type ensures that the old wallpaper can be easily removed in its dry state when it is time to re-paper. Non-absorbent, hard surfaces, on the other hand, such as plastics or old enamel varnish, must first be roughened by sanding, in some cases treated with a stripping compound, then grounded with a primer coat.
In the past , t was common to prepare walls with a primer paper before wallpapering. This compensated for any tension between the wallpaper and the underlying surface. Such tension appears when the wallpaper swells a great deal when it absorbs water, then shrinks again when it dries. This happens particularly in the case of heavy wallpapers. Nowadays, where most wallpapers have a non-woven web substrate rather than one of paper, things are much simpler. Thanks to modern non-woven wallpapers, one can usually do without lining paper completely. If you have carefully prepared the underlying surface, you can fully enjoy the advantages of non- woven wall coverings in removal and re-papering.
Non-woven wallpapers can be easily handled, form no wrinkles, do not require booking time, conceal small hairline cracks, and are completely dimensionally stable. Even the basic rolled liner paper is more and more often being replaced by liners made of non-wovens.
Lining papers are applied like other wallpapers, in lengths butted against each other. They are usually wider than the wallpaper, ensuring that the liner paper seams do not lie directly under those of the wallpaper itself.
Images & text courtesy of AS Creations, Wallpaper 1×1 – A Textbook For Craftsmen and Those Who Wish To Be