As for cracks in drywall, you need to use a scraper to widen the crack and spot drywall tape in excess of it. Apply a joint or drywall compound and drive from the crack. Smooth in excess of that has a sponge. Then just sand, key, and simply paint it https://colab.research.google.com/drive/1jai29SqruExmP6jWH2ftCg3JrFIb7s7s?usp=sharing