How much wallpaper paste do you need?
Wallpaper paste is easy to underestimate, because walls look smaller than they are once you add up all four of them. A room of 4 by 3 metres with 2.5 metre walls has 35 square metres of wall, and at a typical coverage of about 0.2 kilograms of ready-mixed paste per square metre, that room needs about 7 kilograms of paste, or seven one-kilogram tubs. The calculator above works from your room's length, width and height to give you the wall area, the paste weight and a tub count, plus a rough roll estimate so you can plan paste and paper together. Buying one extra tub is cheap insurance: running out halfway through a wall leaves a seam to dry and a visible join.
The wall area formula is simple: twice the sum of length and width, multiplied by height, gives the total wall area, and that is the starting point for both paste and paper. In practice you should deduct large openings such as doors and windows, which can save a roll or two in a room with big windows, but do not deduct small features, because offcuts and pattern matching consume the saving. Patterned papers waste more than plain papers, since each drop must be cut to align the pattern, and that waste applies to paste too, because you paste the wall or paper for every drop including the trimmed parts.
Paste-the-wall versus paste-the-paper
Modern wallpapers fall into two camps, and the paste method matters for both quantity and technique. Paste-the-wall papers are hung by pasting the wall directly, which is faster, lets you slide the paper into position, and means the paper does not expand and shrink while you work. Paste-the-paper wallpapers are pasted on a table, folded, and left to soak for the manufacturer's recommended time, usually five to ten minutes, so the paper expands before it goes on the wall. Skipping the soak time is the most common cause of bubbles and gaps, because paper pasted and hung immediately keeps expanding on the wall and then shrinks as it dries, opening the seams.
Coverage differs slightly between the two methods, because paste-the-wall work tends to use paste more evenly, while paste-the-paper work loses some paste to the table and to trimming. Ready-mixed paste is convenient and consistent, and its coverage is usually stated on the tub, commonly around five square metres per kilogram. Powder paste, mixed with water, is cheaper per square metre and lets you adjust the thickness, but it must be mixed lump-free and left to stand, and a badly mixed batch causes lumps under the paper that show through, especially on smooth, light papers. For a first attempt, ready-mixed paste removes one variable from a job that already has several.
Preparing walls for a lasting finish
Wallpaper shows every flaw in the wall beneath it, so preparation is most of the job. Strip old paper fully, or at least remove loose and peeling sections, fill cracks and holes, sand smooth, and wipe away dust. New plaster must be sealed, or it will absorb paste unevenly and the paper will bubble and lift; a diluted coat of paste, known as sizing, or a dedicated primer, does this job and also makes future stripping far easier. Old painted walls should be washed to remove grease, especially in kitchens, and glossy paint should be lightly sanded so paste can grip. Lining paper, hung horizontally, hides minor imperfections and gives a smoother base, and it is worth the extra day on walls that are less than perfect.
Measure and mark before you paste anything. Find the starting point, usually a corner or a focal wall, and draw a vertical plumb line, because walls and corners are rarely truly vertical and a paper hung by eye will drift visibly across a wall. Plan the layout so that the final drop in a corner is not a narrow sliver, which looks poor and is hard to handle, and so that patterns centre on focal points such as a fireplace or a bed head. A few minutes with a tape measure and a pencil prevents a layout that looks wrong for years.
Hanging technique that avoids bubbles and seams
Hang the first drop to your plumb line, not to the corner, smoothing from the centre outwards with a brush or plastic smoother to push out air. Overlap into corners slightly and trim with a sharp blade and a straight edge, changing the blade often, since a dull blade tears paper and leaves ragged edges. Seams should butt tightly without overlapping, and a seam roller, used lightly, closes them without squeezing paste out onto the face of the paper. Wipe paste off the paper face immediately with a damp sponge, because dried paste on the surface shows as shiny patches, particularly on dark or matt papers.
Temperature and humidity affect the result more than most beginners expect. Paste dries slowly in cold, damp rooms, which can cause sagging and mould behind the paper, and dries too fast in hot, draughty rooms, which causes seams to open as the paper shrinks. Aim for a normal room temperature, close windows and doors while hanging, and do not turn heating up high to force drying. Let each wall dry naturally, and resist the urge to reposition paper once the paste has started to grab, since moving it stretches the paper and guarantees a seam gap when it dries.
Choosing paste, paper and tools
Match the paste to the paper weight: lightweight papers need a lighter paste, heavy vinyls and textured papers need a stronger, thicker paste, and some papers specify a particular paste type on the label. Using a light paste under a heavy paper is a common cause of paper peeling at the edges within months. Tools are simple and cheap: a pasting brush or roller, a smoother, a sharp trimming knife with spare blades, a plumb line or spirit level, a seam roller, a sponge and a bucket. A pasting table makes paste-the-paper work far easier, but a clean, flat table covered with lining paper serves just as well for a single room.
Budget for waste honestly. Pattern repeat is the key figure: a paper with a 64 centimetre repeat wastes more than a paper with a 32 centimetre repeat, because each drop must be cut longer to align the pattern, and the offcut from each drop is unusable. Random match papers waste least, straight match papers waste more, and drop match papers, where alternate drops are offset, waste most of all. Buy all rolls from the same batch number, since colours vary slightly between batches and a batch change halfway across a wall is visible in daylight even when the pattern matches perfectly.
Removing wallpaper without destroying the wall
When the time comes to redecorate, removal method depends on the paper type. Strippable papers peel off in sheets, washable papers need scoring and soaking, and traditional papers need a steamer, which softens paste quickly but can damage plaster if held in one spot too long. Soak in sections, work from the bottom up, and remove paste residue with warm water and a sponge, since old paste left on the wall interferes with new paint or paper. If the wall was sized before papering, stripping is far easier, which is another reason to size new plaster properly in the first place.
- Wall area is twice length plus width, times height.
- Allow about 0.2 kg of paste per square metre, and buy one tub spare.
- Soak paste-the-paper for the full recommended time.
- Size new plaster before hanging anything.
- Hang to a plumb line, not to a corner.
Measure your room, let the calculator give you wall area and paste weight, and buy one tub more than the maths says. Paste is cheap, a half-finished wall with drying seams is not, and a well-pasted wall is the difference between paper that lasts a decade and paper that peels in a year.