I'm looking to cover some metal steps with natural stone tile. These are exterior metal steps with raised safety-tred diamonds. There is a slight bit of rust, but overall they are super sturdy.
Since I can't get them out, I'd like to cover them with travertine tile (though I'd be open to another kind of tile, maybe porcelain?).
I'm wondering, what kind of mortar or thinset can I use? I know that normal thinset has trouble bonding to metal, but since these are rough, horizontal, and have raised tred diamonds that I could use something like Flexbond or Versabond. Epoxys are very expensive and difficult to work with, or so I hear.
Also, since I live in DC, there are some freezing cycles in the winter. Could I get away with using travertine stone, or should I use porcelain tiles?