Electric mirror may crack under the follow conditions

1, There is no gap between mirror and hard substances.

There is no gap between mirror and hard substances.
If there is marble or ceramic tile round electric heated mirror, and mirror is concaved in this hard substances, and there is no gap between mirror and hard substances, mirror may crack during heating of expansion

2, After installed on wall, mirror bottom line has nail or rigidity substances
In order to keep mirror stable and flat, and ensure there is no marble or ceramic tile on the bottom, so need some soft substances to fill. If people misused hard substance, mirror may crack.

3, The following 3ways digging may cause mirror crack.

1,mirror with rectangular hole for switch or other appliance.
2, mirror with a hole exceed diameter 50mm, for tap or other purposes.
3, mirror has inner angle as shown on the drawing.