Tiles to a lintel?
 

Following on from my earlier post. I've taken down some tiles on a
concrete lintel (Garage door, inside the house since extension in 90's)

The tiles were stuck with a white tile adhesive on a mortar plastered
over the lintel. The bond between the tiles and mortar was excellent
(phew!), but the bond between the mortar and the lintel concrete is
weak.

Is there any reason why I can't stick the new tiles directly to the
concrete lintel? The mortar was there, I suspect, to level with the
pillars, and I won't have that problem for other reasons.

R.