how do I prevent mildew/rusting in bathroom mirror?

If this is on the back side of the glass, the silvering is going bad on the mirror. It sometimes just happens but Windex will kill it very fast. If you must use a window cleaner, don't let it get to the bottom.

check with your auto glass shop for replacement mirrors cut to size with various edges. see mirror trim kits. see hdsupplysolutions.

Well, you have suggestions on how to get the cleanup done.

To stop it from happening, you need to do two things.

1. Open the door after a bath or shower, to let the concentrated humidity out of a small space.
2. Run a fan, so that the humidity moves away from the room.

The bathroom fan will not do the job, unless you have a very good vent and a very good fan.

So any ideas as to why this is happening (only bottom side). Is it because moist fills space from bottom -> up ? More importantly, would filling with silicone the bottom part solve my problem ?

You won't know until you try it. Good luck.

Joe

You won't know until you try it. Good luck.

Joe

Common silicones cure by reacting with moisture and release acetic acid. The (vinegar) acid is volatile and will probably dissipate quickly before any significant effect on the mirror coating. Worth a try, since the mirror protective layer may already be history.

Joe