The algorithm for applying the primer is as follows:

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penetrating acrylic primer;
a stepladder or a sturdy table - will be needed when working in hard-to-reach places and at the junction of the wall and ceiling;
microfiber roller;
extension handle for roller;
paint brush for hard to reach areas;
cuvette (special ribbed tray) for primer.

the surface of the gypsum board is cleaned of dust and dirt;
the primer is diluted to the required consistency - the car owner data of water and primer can be found in the recommendations printed on the packaging;
the soil is poured into the tray;
the roller is thoroughly wetted, after which the excess primer is removed on the ribbed surface of the tray;
The plasterboard is primed. It is necessary to start from the top and move downwards to avoid drips. If drips do form, they are removed with a semi-dry (used) roller;
corners and hard-to-reach places are primed with a paint brush;
After the first layer has dried (you can find out how long it takes for the first layer of primer to dry on the packaging), a second layer of primer is applied.
After the primer has completely dried, proceed to applying the putty.

Experience shows that plasterboard must be primed before puttying in the following cases:

Sealing of seams and heads of fasteners is carried out;
wallpaper will be glued onto the plasterboard;
The final finishing with decorative plaster is provided.
You can do without soil:

when using waterproof plasterboard;
painting walls or ceilings if the surface is immediately covered with finishing putty.