A number of factors cause wallpaper to dry slowly. This means there is no set time to wait before you apply a border. You have to study the specific circumstances of your decoration out when it will be possible to apply your border. In all cases, you have to let the wallpaper dry completely before hanging the border. The border adds extra weight to the top of the wallpaper and so could drag it off the wall before the adhesive sets.
Newly plastered walls absorb, although they may seem dry, actually still retain a lot of moisture. You should leave plaster at least four or five days to dry and apply a sealer to the walls before wallpapering. The sealer should cut out the effects of damp wall plaster. Paper hung over walls that have many coats of oil-based paint will also take longer than usual to dry.
Cloth-backed paper will dry quicker than regular wallpaper. Vinyl paper takes the longest because it seals the walls, making it harder for the moisture in behind the paper to escape.
When wallpaper dries out too quickly, it shrinks, causing the surface to retract and leaving a white line of the base paper visible along the edge. Therefore, you should not apply heat in the hope of being able to apply your border quicker. The most important aspect of drying wallpaper is not heat, but ventilation. If your house has a lot of moisture in the air, you will probably already have a dehumidifier. Putting this in the room is a better bet than a heater. When you shower or run a hot bath in a newly papered bathroom, leave the door open, or open the window a little to let the steam escape.
Over-pasting wallpaper will extend its drying time. If there is a thicker layer of paste behind the paper, you will have to wait longer to paste your border. Similarly, over watering pre-pasted wallpaper is a doubly bad idea. For one thing, wetter paper will take longer to dry, but it is also possible to wash the paste off the paper.
Regular paper that is not over-pasted and is not in a damp room should dry overnight. Paper hung on gloss paint and vinyl paper will take longer. In these cases, leave the paper two days to dry before pasting your border on top of it.
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