Step 1 - Check your wall and specification

Your mirrors must be either 5mm or 6mm thick and must be safety or foil backed. Check your mirror thickness and also the back of the mirror to see if a film has been applied. 

You must not install 4mm mirror or non safety backed / foil backed mirrors into J channels as this is unsafe.

Check your wall is strong enough to support the mirrors. For stud walls you will need to find the studwork joinery to attach to.