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Before wallpapering, take care to prepare the room and wall surfaces.
The surface to be pasted must be strong, clean, dry, neutral in colour, uniform in colour and sufficiently absorbent.

Preparing walls for wallpapering
Make sure there is no dampness on the walls
Remove all unnecessary items from the walls
Drops of moisture, dampness and fungus may appear on the walls. If you find such signs in the room, eliminate the causes of high humidity. If necessary, carry out antifungal treatment.

There should be no foreign objects (brackets, fasteners, nails) on the surface of the walls. If old wallpaper was pasted in the room, wet it with water and remove it with a brush or spatula.

Alignment of walls
Make the walls smooth
Treat the walls with primer

Apply the primer in an even, thin layer to the wall using a roller. Avoid splashing the primer onto the ceiling and floor. It is recommended to choose a deep penetration primer.
Then you should properly prepare the room where you will be gluing the wallpaper.

Turn off the power before wallpapering.
Turn off the electricity
Tidy up the room

Before gluing wallpaper, it is recommended to turn off the electricity in the room.

Clean the room and remove dust. Dust particles can stain the wallpaper, harm your health, settle on the glue and primer.

There should be no foreign objects on the wall surface (brackets, fasteners, nails). If old wallpaper was pasted in the room, wet it with water and remove it with a brush or spatula.
 Before wallpapering
Close windows and doors tightly
Lay plastic film or cardboard on the floor
Close all windows and doors to prevent drafts in the room.
  
This will protect the floor, allow you to conveniently lay out the wallpaper strips and prepare for pasting.
Once the walls are prepared and checked, and the wallpaper is purchased, there are still a few things to do.

Before gluing
Make sure all rolls are the same. Use only one batch of vinyl wallpaper for one room.
Make sure all rolls of wallpaper are identical in pattern, color and size.

Joining the drawing
Please clarify the information about the pattern joining
The type of wallpaper joining is indicated on the label in the form of arrows indicating the location of the strips to each other. This is necessary for the correct matching of the pattern on adjacent strips. Please note that when using wallpaper with a large pattern, you will need a reserve of rolls for joining the pattern, which will increase the total consumption of strips.

Make a wallpaper adjustment   
For calculations, use the ceiling height and the perimeter of the walls of the room. For convenience, you can cut all the panels at once, having previously calculated the height of each strip. The trimmings of the strips can be useful as a reserve. To avoid confusion in the order of the strips, number them, making marks at the top and bottom of each strip.

When gluing, there is no need to match the pattern (the wallpaper is patternless and is glued without alignment)

The pattern is straight (identical patterns are joined to each other at the same height)

Shifting pattern, diagonal arrangement. Shifted fit (fitting according to the pattern, i.e. the subsequent panel is glued with a vertical shift relative to the previous one)

The pattern is not defined (counter gluing). Each of the subsequent panels is glued in the opposite direction relative to the previous one.
How to prepare wallpaper glue
Prepare wallpaper glue
Apply glue evenly to the wall

Wallpaper glue is selected according to the manufacturer's recommendations. The glue is poured into a container with water while stirring constantly. After some time, the glue will swell and resemble jelly. Now it can be used.

The glue is applied in an even layer to the surface using a roller or brush. The top of the wall is carefully coated with a small spatula. Excess glue is removed with a sponge soaked in water.

How to apply glue
If you are gluing paper-backed wallpaper
If you are gluing wallpaper on a non-woven base

The glue is applied both to the wall surface and to the canvas itself. Before pasting, spread the wallpaper on the floor. Coat the paper-based wallpaper with glue, then fold it in half and leave it to soak for 6-8 minutes.

Apply adhesive only to the wall surface.
 How to apply glue
Where to start gluing wallpaper?
It is recommended to do this from the corner or door/window openings, since these lines are perpendicular to the floor. It is advisable to use a plumb line or level so that the strips are glued evenly. You need to finish pasting in some inconspicuous place - above the door or in a corner where the wall is hidden by furniture or curtains.