Repair the old plaster yourself

Hello everyone,
My name is Paul, and I am new here in the forum. I’m not exactly sure if my question is in the right place, but I would still like to ask it:
It concerns an approximately 60-year-old former car and agricultural machinery workshop which, despite being out of use for a long time, is still primarily used for private purposes. By now, quite a few things are coming loose, such as the interior plaster due to numerous renovation works over the past years. Holes and various damages have remained. Now a small "restoration" is due.
The problem: I have certain ideas about how the work should be done, namely I would like to do the painting and plastering myself and only renew the plaster in the damaged areas. Therefore, these newly plastered areas should look exactly like the old ones. Practically, one should hardly see any difference from old to new. I can gladly take pictures. The plaster is as old as the workshop and is smooth and, so to speak, rough or sloppily applied. Nowadays, houses are usually plastered rough and very evenly. But I do not want that. I am sure some will shake their heads now because this is not a residential building, but the workshop should become a little jewel again, and since, for example, the electronics and the roof have been renewed, the walls should also look nice again and especially as they did before. Therefore, I would like to know which cement is best suited for smooth walls.
I hope I have expressed myself clearly and understandably.
I would appreciate any answers.
Best regards, Paul

Hi, of course, why not. Such an outbuilding is ideal for testing your skills. Only one statement makes me suspicious, you only want to do some touch-ups, but you shouldn't see any difference from the old plaster. I would apply a complete base plaster and even out the irregularities. Then paint over it. Everything else just makes things worse.

Hello Paul,

for material identification, take a fallen crumb to the plasterer or let one fall, not too tiny. A repair is always visible. And if you go too thin over the connection points, these are predestined as fault areas. What hilfehilfe says is correct. Fill holes below the overall level, maybe apply some siliceous acid as a primer on the wall, depending on what material it is, then apply the topcoat from wall to wall. You don't have to spray it, applying might also be sufficient. You should not go below the minimum thickness, it says on the bag. I would definitely look for loose spots and remove liberally down to solid material. However, these are experiences from monument preservation.

Best regards
Gabriele