A
Aztectiler
Deffo use mirror mate adhesive and not Silicon....the acitate in Silicon can eat into the mirror backing and ruin it....
This is absolutley the right advice. Normal Silicon has an acid in it that eats into the chrome backing of mirrors and will, in time deteriorate the mirror finish from behind.
Please use the correct product that is specificly made for the job in question "MIRROR ADHESIVE"
I have just completed a bathroom with this feature incorporated in it. Adhesive and screwed hardibacker to the wall and then fixed mirror with mirror adhesive.
Looks Fantastic!
Good Luck