A clear understanding of the next steps will help simplify the task.

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set of spatulas - narrow, medium, wide;
plumb line and level to check the evenness of the surface or laser level;
a piece of sandpaper, a sander with a cutting and polishing wheel;
wide brush for applying primer;
impact drill;
polyethylene film, scotch tape (preferably masking tape);
screwdriver;
hammer;
mixer attachment for drill;
plastic mixing bucket;
rags and a sponge.
You only need a few materials:

primer to improve adhesion;
putty for leveling the surface;
solvent to remove old paint.
If the walls that need to be prepared are covered with wallpaper, you will need a sprayer. With its help, the wallpaper is torn off by soaking it. Once everything is prepared, you can start working.

Stages of work
This is not a set of actions, but an costa rica mobile database step-by-step process. Preparing walls for decorative plaster includes the following stages:

Surface cleaning.
Surface leveling.
Priming the surface.
Puttying works.
The technology implies correct and precise execution of these stages. For this, it is important to consider each of them in detail.

Surface cleaning
It doesn't matter whether the surface is being prepared in a new building or it is a living room undergoing cosmetic repairs. The primary task is to ensure high-quality adhesion to the surface. To do this, it is cleaned of all unnecessary things. Step-by-step instructions:

Inspection of walls and their assessment. At this stage, it is necessary to understand whether alignment is required. The walls are checked with a plumb line and a level.
If there is an old layer of finishing on the wall, it needs to be removed. This includes old wallpaper, paint, a layer of putty. All the tools are used: a grinder, a spatula, a solvent, a sprayer.
If we are talking about putty, then you will have to tinker with its removal. Despite the thin layer, the adhesion of the material to the surface is excellent, so you will not be able to simply scrape it off. A special solution will help simplify the task. You need starch and water. They are combined in a ratio of 1:20 or 1:15, if the case is especially difficult. It remains to wet the walls with putty with the solution and wait 20 minutes until it is absorbed. After this manipulation, the putty will be easily scraped off with a spatula. Putty can also be removed with an impact drill. This process is also quite labor-intensive.
To remove paint, you need to know what type of paint and varnish material was used. If it is water-based paint, then a piece of newspaper is glued to the wall and after drying, it is torn off together with the paint. If it is oil paint, then you will need a building hair dryer and a spatula. Under the influence of temperature, the paint cracks, shrinks and is easy to scrape off the surface. Solvent is a universal option, suitable for almost any type of paint. The solvent is applied to the surface from above with a brush. After 3-6 hours, the paint will soften and can be scraped off.