My son through a baseball in the car knocking the rearview mirror off the windshield.
Now get this... The adhesive between the baseplate and the windshield did not fail; the glass did.
To be accurate, 2/3 of the adhesive between the baseplate and the windshield did fail, but 1/3 did not resulting in a dime-size piece of windshield still attached to the baseplate.
I assume the best adhesive to re-attach the baseplate-to- windshield surface is still rearview mirror adhesive, but what is the best adhesive to re-attach the glass-to-glass surface?
Any decent auto parts store will carry a repair kit to reattach the mirror to the windshield. Included will be cleaner and some two-part epoxy, and instructions. I suggest you reattach the mirror in its original position...
If the chip is still attached to the mirror stalk, yes, try to fit the mess back in its original position, and let the epoxy hold it all together. If that chip didn't come off the stalk, it's likely not going to come off, ever...
JB Weld has steel in it, and is not clear. Get some 5 minute epoxy, usually sold in a two tube "syringe", for lack of anything better to call it. Mix a small amount and use a piece of scotch tape to hold it up while the epoxy sets up.
The other posters suggest putting it in the same place, and using the chip to fill the hole, and hold the mirror.
I advise against this for a couple reasons. The lower mirror, or off to one side by 3/8ths of an inch will not be noticeable, or not by much. The glue used to attach rear view mirrors is very particular about having a perfectly smooth, clean place to attach. If there is any gap at all, more than a _molecule_ or two thick, it will not hold. That is why I think a new location is desirable.
As to using epoxy to attach the chip, and thus the glass, it will be difficult to get the bond to be strong enough, but even more difficult to support the weight of the mirror, or the metal plate that the mirror hangs on, while the epoxy sets. The mirror adhesive you get at the auto parts store cures almost instantly, enough to hold the metal plate, at least.
Epoxy is difficult to make a strong enough bond to successfully hold a mirror. Ask me how I know that!
I might add that this was in a work van, that frequently was used on very rough surfaces, on jobsites, and in developments. It did not work for me, and I am well versed in using various adhesives.
The parts houses around me have the cyanoacyllate glue. Which didn't work well for me. On my full size van, I cut a chunk of wood to size. Screwed it to the sheet metal over the windshield. Bracket the miror shaft to the bottom of the wood. Works fine.
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.