As for cracks in drywall, you need to use a scraper to widen the crack and put drywall tape around it. Implement a joint or drywall compound and press throughout the crack. Easy more than with a sponge. Then just sand, key, and simply paint it around. Instruction booklet in https://colab.research.google.com/drive/1jai29SqruExmP6jWH2ftCg3JrFIb7s7s?usp=sharing