Humidity im salt mix

[saraiva]

With chemical product is used to prevent hardening or humidity im home made (DIY) salt mix

 

[bkiba]

I think they add some sort of power lubricant to the salt mix to keep it from binding (in pharmaceuticals I think this is silica powder). The salt is very hygroscopic so it is going to absorb water no matter what

 

[Randy Holmes-Farley]

I personally wouldn't add anything to do that. I'd just keep it tightly closed.