I'm installing a floating sink and think I need to install blocking between the studs. I would normally open the drywall at the correct height and use a 2x6 between the studs. But this is going into a high-rise condo building and the studs are metal (not wood)... is there an alternate solution? Also, if the wall is tiled, is the additional behind-the-wall support needed? or should the tile and mortar on top of the drywall be sufficient support?
You can install wood blocking between metal studs, but you'll have to open up more of the wall to attach them (you obviously can't toe nail them). Notch the block so it fits into the channels in the studs, then just attach it with screws going through the studs.
I wouldn't hang a sink on tile without some sort of additional support. Even if the tile were strong enough to hold it, it would provide a point of leverage against the wall that could introduce flexing.