Why do Koreans throw salt at people they don't like?

The specific reason is not clear. I asked the Korean person in my company, but he didn't explain clearly. Just say this: If a guest comes to the house, and the guest's behavior makes everyone dislike it, after the guest goes out, salt (coarse salt) will be sprinkled on the door, which means that he will not come again in the future, and he is not welcome.

Another situation is that when the atmosphere is not good, sprinkle some salt, and then everyone will stop the unpleasant topics and re-establish a good atmosphere.

But why he did this and why he used salt instead of anything else, he didn't explain clearly.

Maybe his Chinese is too bad, or maybe my Korean is too bad.