1. Keep the walls clean and dry.
2. Apply adhesive tape to the crack and press it tightly.
3. Make sure that the gap is covered by the tape, then use a knife to cut the excess tape, and finally brush the mortar.
4. Let it dry naturally, then lightly polish it with a construction hammer.
5. Fill with enough paint to make the wall surface smooth.
6. Remove the leaking tape. Then, notice that all the cracks have been properly repaired, and use fine composite materials to modify the periphery of the joint to make it clean and new.