Question: We’ve been trying to get the metal button of a rear-view mirror to bond to a new windshield. We’re in the summer heat of Las Vegas where it is routinely over 110°F―and even hotter inside a closed car. We’ve tried all the typical glues but, while the button will cure and hold, it falls off when the mirror is attached. It will sometimes hold for a few days; other times, it’s just a few minutes. We’ve followed the instructions to the letter, but the bonds always fail. We’ve even tried the special superglue that touts glass-to-metal bonds. When the car gets hot, the mirror always falls off.
Answer: I would certainly recommend one of the leading brands of rear-view mirror adhesive. They have been used all over the world for many years in both hot and cold climates. That’s not to say that there have not been failures, but they are rare.
First, you need to make sure that all the old adhesive is completely removed from the button and that the glass is cleaned with an alcohol wipe. Second, follow the instructions exactly (apply activator on the windshield only and not on the button). For maximum strength, leave the button in place in the heat for 24 hrs before attaching the mirror.
We occasionally come across some windshields where the button will not adhere. Most of the time, they are aftermarket/replacement windshields with a painted/etched area where the button is adhered.
If the acrylic rear-view mirror adhesives do not work in your situation, consider a 5-min epoxy adhesive. These tend to soften and weaken at around 120°F, but if you post-cure them with the heat inside your vehicle before attaching the windshield, this softening temperature is increased. ASI
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