by ACourtney » Wed Oct 19, 2016 11:19 am
The glass only needs to be cleaned with a suitable degreaser and then primed. As John has suggested any scratching/abrading of the glass will be seen from the outside, so unless you had this gently sand blasted (as used to etch number plates onto glass and for decoration on some custom cars) it probably wouldn't look very pretty. If you take care masking up the inner edge for the primer then it should look okay.
One tip, that came from Alan Donowho when he did the heated windscreen group buy, is to prime the edged of the glass to make sure that the bonding agent seals across the laminate section. That will help prevent ingress of moisture between the glass and plastic layers of the screen.
The GRP surface of the screen surround should also be prepped by cleaning with a solvent and it would benefit from being roughed up with some coarse grit - P180 or P240. Failure to prep this surface properly is probably at the root of most of the leaks suffered by Midases. Our cars were all moulded with wax release agent, as that is what gives the gelcoat the gloss finish out of the mould. Consequently, the surface of new gelcoat is rich in wax. If you want to bond something to that gelcoat, or paint it, then you need to clean off the wax. Roughing up the surface will also improve adhesion.