[quote=@RolePlayerRoxas]
 Does he need to directly touch something to turn it into an explosive?
[/quote]

Yeah. Inorganic materials. Also, he does need to directly touch the object. He gets a little leeway thanks to Killer Queen, the very Stand that allows him to create explosives, but it's such a short range that he still needs it to directly touch the objects.

I'm also gonna say that he doesn't have access to Sheer Heart Attack for simplicity's sake.