I've never had a problem with de-icer damaging the paintwork. I think some people have been daft enough to use anti-freeze instead, with disasterous results. That stuff belongs in your radiator and nowhere else
I cleared the windscreen with de-icer this morning while I left the engine ticking over. The temperature gauge hadn't started to climb the scale, but then it doesn't until I get on the motorway on mornings like this (damn the thermal efficiency of the diesel engine!) I sat in the car and revved it a bit (I know it uses more fuel, but I feel it's kinder to warm it up quickly than to let it idle up to temperature) and as the screen wasn't showing any signs of fogging up again, I started to drive.
Within 30 seconds of hitting the main road, I couldn't see a damned thing. The whole windscreen had frosted over again. I'm guessing that the sub-zero temperatures, combined with the wind chill factor of the car moving through the air makes even the de-icer freeze on the windscreen.
So if I have to do it again in the morning, I'll be removing all moisture (including de-icer) with a squeegee to see if that helps. Though using the wipers didn't, so I'm not sure what the answer is.
It's Renault's fault really. If quick clear windscreens had been optional on the diesels when I'd ordered mine, then I'd have had one. But for some reason, they only did them on the petrol engined models at the time.