Answer
Only sand the exposed glass edge of a mirror. Use 600, 800, and 1000 wet with very light pressure.
Why it happens
Mirrors are glass with a reflective backing that can be damaged by moisture, pressure, or edge chipping.
Recommended grit
For exposed glass edges only, use 600, 800, and 1000 wet with very light pressure.
Wet or dry
Wet on the glass edge only; keep water away from vulnerable backing.
Success check
The glass edge is smoother without chips or damaged backing.
What to do
- Inspect whether the edge is plain glass or near mirror backing.
- Use very light pressure on the glass edge only.
- Start with 600 and refine with 800 and 1000.
- Dry the edge completely after sanding.
Avoid: Do not sand the reflective backing.