Salt is used in Scripture as part of the required sacrifices made at YHWH's altar (Leviticus 2:13; Ezekiel 43:24), and it was also an ingredient in the incense that was to be burned before the LORD (Exodus 30:35). From these Scriptural references, we see that salt was important in the practices that delineated between what was sacred (set apart) and what was not.
For this reason we use salt to prophetically state that the land/space or items belong to the LORD. Salt being scattered functions as a symbol of these items being set apart to the LORD, this also informs the supernatural (unseen) realm that these items belong to the LORD and not the kingdom of darkness. The salt in and of itself is not powerful, instead it is a physical demonstration of choosing the kingdom of the LORD and setting things apart for His ownership and glory.
You can use whatever salt you have on hand. Simply pray over what you are going to use stating that you are dedicating it to the LORD and that using it symbolises the items (land and/or property) being set apart for Him.