Even professionals will from time to time experience one or more of the most common problems that occur when you work with wallpaper. Don't panic. Even when things seem to be going badly wrong, there is usually a very simple cure.

Unsightly Marks

Wallpaper can discolour if it is hung on walls that have not been properly sealed or if you happen to get some paste on the designed face of the paper. Remember that colours will fade if they are subjected to strong sunlight. Occasionally, you may find small patches of mould growing on wallpaper. This could be due to damp walls or heavy condensation, or old patches of size or paste left on the walls at the preparation stage. While wallpapers will cover minor defects in walls, the cause of any damp must be checked before you cover it up. Rust spots can show up if you hang paper over steel pins that have not been sealed. When preparing a wall for papering, check it carefully and mask or seal any old nails or pin marks before you line it.

Paste Problems

Where you have difficulty matching up the pattern on two drops of paper it is likely that your pasting technique is at fault. Under- or over- soaking the wallpaper reduces its ability to adhere to the wall and makes the paper difficult to handle. Follow the paste manufacturer's instructions regarding proportions, mixing and setting times: too thick a paste will cause bumps and lumps, too thin and the water will over-soak the paper, which can cause it to tear. Blunt scissors won't cut a true line, and the edges of the paper will become frayed; keep wallpaper scissors clean by wiping off the blades after each cut. If your wallpaper starts to fall off the wall in complete strips it's because you didn't line your walls first and there are patches of distemper that have made the paste lose its stickiness. The only solution is to take the wallpaper off the walls, clean the walls and, where necessary, apply a stabilizing solution. Then line the walls and re-hang the wallpaper.

Seam Trouble

When two drops of paper have not been butted together closely enough, you may find a narrow white seam showing. Make sure you soak the paper for the correct time or it could shrink as the paste dries. Sometimes heavier and darker wallpapers are manufactured with a white edge, and the makers provide special colour-matched pens for you to obliterate the white. Seams that don't stick are nearly always caused by not lining the walls before hanging paper. Carefully lift back the seam and apply a little strong adhesive with an artists' brush then roll the paper back into place with a seam roller and wipe the seams to remove excess adhesive. If the paper has a raised pattern, don't press too hard on to it or you'll squash the pattern. Seams should butt up against each other, not overlap. If they do, you might find the seams don't stick, so treat these as you would for lifting seams.

Bubbles

Bubbles in wallpaper are probably the most common problem experienced by the home decorator. Sometimes bubbles will disappear when the paste has dried out, so it's worth waiting a while before tackling them. If a bubble seems to be full of paste it could be because you applied a little too much, or when you were smoothing down the paper on the wall you overlooked smoothing downwards and outwards towards the edge. Simply pierce the bubble with the sharp tip of a craft knife or scalpel and allow the excess paste to escape, carefully sponging down the 'empty' bubble afterwards to clean any paste from the face of the paper. Sometimes bubbles are full of air - perhaps this bit of paper did not receive any or sufficient paste - again, pierce the bubble and use a fine artists' brush to apply a very little paste and smooth the bubble down with a sponge.