1: Look at the bottom of the ceiling where the crack is shoveled. 2. Dig a small edge with a knife (this problem should be that the edge was not shrunk before, or it was too small). 3: Go to the greasy powder shop to buy a set of anti-crack treasure, water and powder. 4. Fill the prepared anti-crack treasure into the edge. When it's dry, put a white cloth on it. It's better than kraft paper. It will be brittle when it is dry. Just scrape the putty again. It's important to dry the first time and then shave the second time. Then wait until it dries before shaving. Then when it's done, it will be polished and painted. Do as I say, and it won't crack again. I am a project supervisor, and I have encountered many such maintenance projects before, which makes many owners very angry. Woodworking is very important. If you want to leave a seam of 1cm on the woodworking ceiling, don't think it is good or bad not to leave a seam.