My brother has a service station and he uses silicon RTV and has had good luck with it. He uses a small dab then holds the mounting plate for the mirror in place on the windshield with some masking tape overnight.
As part of the windshield prep, scrap any old adhesive residue off with a single edge razor blade.
Silicon RTV is a Room Temperature Vulcanizing elastomer ("rubber"). The stuff you get in the hardware store works by absorbing water from the atmosphere to cure. As it cures, it emitts acedic acid vapors, hence the "sharp" smell of RTV curing. Silicon RTV offers good adhesion and is compliant (flexible) offering allowance for the different expansion rates of the windshield glass and the metal base plate, also, the compliance helps it deal with physical vibration.
Typical mirror repair kits use cyanoacrylic (I think that's how it's spelled) adhesive. This stuff is an acrylic monomer that rapidly links into a polymer (cures) when 1. atmospheric oxygen is excluded and 2. in the presence of moisture (it doesn't take much the typical moisture layer on things is enough to cure it). Cyanoacrylics offer excellent adhesion but are fairly ridgid (brittle). BTW, acrylics are soluble in acetone, so acetone is usually a good cleaner for the old adhesive. I'd go the extra step of cleaning the area with alcohol after cleaning with alcohol.
If it were me, I'd try the mirror repair kit first, because it's easy and fast. Prep is critical. Just don't use too much adhesive, this is a case where more is not necessarly better. If I didn't have good luck with the cyanoacrylic, then I'd go the extra step and try the silicon RTV.
[ July 20, 2003, 10:00 PM: Message edited by: Rick in PA ]
