Actually Salt has been used to ward off evil spirits in a bunch of Asian cultures. Buddhism and Shintoism coming to mind in particular. 

A [url=https://books.google.com/books?id=vHjy-dPPUMUC&pg=PA65&lpg=PA65&dq=Buddhist+Salt+evil+spirits&source=bl&ots=7Jnw1ZYpoZ&sig=sweGK4eiltQxIGFCZlf0j9VGRZE&hl=en&sa=X&ved=0CE0Q6AEwCGoVChMIm9fiz4fDxwIVyZiACh38mw4E#v=onepage&q=Buddhist%20Salt%20evil%20spirits&f=false]random book from 1988[/url] makes it easily predate Supernatural (Which Spiderwick did already). I'm also pretty sure that there is some evidence in Roman Tradition as it would be used as an offering to the gods often times to keep malice out of the house. 

Christianity has also used it as a curse to keep all things out. 

"Abimelech fought against the city all that day, and he captured the city and killed the people who were in it; then he razed the city and sowed it with salt." (Judges 9:45)