I'm not sure I'd trust the salt to make it that unreadable...and hammering the outside casing only warps the platters a bit. So for a low tech destruction on a drive that can't be electronically burned (or shot...), I go with disassembly, fold the platters in half by hand (surprisingly not that hard), and then hammer a sharp crease in the folded platter.
It's certainly not the best way, but entertaining.
Entertainment and catharsis are important, yes.
The salt is just to increase electrical conductivity and help corrode it over time. They're at the bottom of a large garbage bin.
...But this part was really more of a question. Like, for someone with professional data recovery equipment (and a 3 letter name..). What impact would the corrosion really have on the readability of the platters? I'd almost swear I'd seen it done on a DR companies promotional video somewhere.
A few of them really did cave in nicely though. Not as deep as the shotgun blast though.
Here again it's a question of professional DR folk being able to straighten the platter if the metal hasn't been deformed (as in silly putty level stretched) enough to alter the alignment.
Hell, even with the shotgun blowing a quarter sized hole in the platter (blue shirt visible through drive in blown up photo), TBH I'm not entirely sure pros couldn't glean something useful off the remaining (arguably) pristine section of the disk ... Because DR is nowhere near the center of my skillset.