Scraping before painting only old paint is scraped off, not plaster. it only scratches when there are already more layers on the wall. Normal leveling of the walls is done with plaster, minor unevenness is leveled. If the wall is more damaged, uneven, you can also use the final paste for plasterboard and trowel to level the surface until smooth. If the damage is greater, the wall can be scraped, penetrated and a new layer of stucco applied. The wall is then like new.