Tiling onto Metal?
Here is the challenge: Outdoor upscale BBQ has tiled counter and tile on the vertical from lip. (See pic 1) The counter is built of a welded steel tubing frame with Hardie board on the top surface but none on the vertical 2" lip. The lip tile was just thinsetted to the metal tubing.
With time and exposure, rust caused the thinset to fail and the tiles to fall off. (See pic 2) The challenge is to replace the lip tiles more securely.
My solution? Strip all tile, grind off all rust with an angle grinder. Apply a bead of polyurethan construction adhesive to the metal, smearing it into a film on the metal. (Pic 3) Using a stick, I tapped the adhesive creating sharp peaks as if you were frosting a cake. When the adhesive dried, there was a solid tooth for the thinset.
Used 1"x4" guide board, clamped to the lip, so the tiles would be perfectly straight. Applied tiles using modified thinset, grouted, then sealed all the grout lines (new and old) twice using sealer. (Pic 4)