Salt and the Supernatural

Salt has for centuries, if not longer, been used in many rituals & instances involving the supernatural. It acts as a repellant against these forces, or as containment. Due to the need for salt, in small doses of course, for animal life and sentient life, it is generally seen as a pure substance & related to life. This has led it to being anathema against the supernatural elements governed by evil, undead, and the demonic.
It seems to disrupt the very essence of the supernatural on a spiritual level, and is an essential ingredient in holy water besides the water & specific blessing. When salt is used against the supernatural, the purity is all important. Pure salt seems to have the strongest effect, followed by those mixed with specific ingredients that also affect the supernatural, such as silver. Salt mixed with anything else can have minimal effect, none at all, or even act to draw it in. Salt that is blessed is stronger still.
Much speculation, besides being tied in with it being tied to the living, has been debated by occultists & mages through the years. Some seem to indicate that the colour too plays a part representing the light, and opposing darkness. Others speculate that since there is a link between death & evil, that anything representing the opposite acts like a conduit & focus for the user to contain or drive off the the former. That and the willingness to use such a precious commodity in such a way.

Manifestation

Regularly sprinkled at doorways to houses and important places, in summoning & banishing circles, and in certain superstitions (like throwing a pinch of salt over the shoulder to blind the devil). In each instance it sucks the negative force in on itself causing damage by weakenng the entity it is in contact with.

Localization

Where the salt is used leads to the disruption of evil, or it's concentration in a specific area. They can communicate with anyone who summoned them but loose the ability to affect the area beyond in any other way. If there is a way not touched by salt leading away the entity can move along this path & flee if need be.

"Aye, it's true. There is salt in holy water. The purity helps to drive of the evil. It is an important part of life so it extends to hurting those that are antilife and feeds of death & evil. If you're stuck, come to me for some. And if you are ever able to speak to a bishop or higher, they only use the purest for holy water."
Father Tossil speaking to Amon the Holy Crusader.