The substrate must be smooth, with good water absorption, free of cracks, free of adhesion restricting substances and sufficiently firm. These properties must be ascertained before wallpapering.
If we need to judge the quality of the plastered surface, it is sufficient to run the palm of the hand lightly over it. If grains of dust stick to the fingers, the strength is not sufficient. A similar test can be carried out with adhesive tape.
Check the moisture content of your plaster. If you do not have a moisture meter, stick a foil of about 0.5 m2 on the wall with adhesive tape. Remove it after approximately 24 hours. If you observe condensation on the inside of the foil or if the area darkens, this means that the plaster is excessively damp. In such cases, it is necessary to wait for it to dry or heat the room with a heat radiator to speed up drying.
Don't forget about water absorption. Before starting work, carry out a water absorption test. Spray water on the wall with a brush or spray bottle. If the surface absorption is good, the base surface will change colour after a short time under the influence of water. If the water absorption is too high, the surface will darken quickly. Grease, oil and tar stains must be removed from the surface before wallpapering. They can cause stains on the wallpaper and, in addition, neither the adhesive nor the wallpaper will adhere to such a dirty surface.
If there is already wallpaper on the wall, it should be removed preferably with water or wallpaper remover or wallpaper glue dissolved in water (approx. 1 box per 8-10 litres). Other products are not recommended, otherwise they may soak into the new surface
If there are cracks in the wall, these should be filled with a flexible grout.
Do not forget a primer, which is very important for unifying the substrate. The primer locks the wall so it won't absorb the glue. Otherwise, the wallpaper may not adhere properly to the wall. And there's nothing worse than sticking expensive wallpaper on a wall that hasn't been treated in this way and then it doesn't stick. We recommend investing the few Euros in this primer and not skipping this step.