Dupont Clear

I just got some Dupont 7779 s urethane and wanted some advice as it is my first time using this type of paint.
Am I correct that it is a 4 parts clear to 1 part activator mix?
It can be shot over decals?
Use a large needle on the airbrush as it flows thick?
Any help would be appreciated!
Thanks
Chris

You're right about it being 4:1, althou I have never used it personally. I use Dupont 72200s and never had any problems with it painting over decals. I find a larger needle and tip work better to get a nice flow-out. 7779s has a flash time of 10 minutes and a dust free time of 20 minutes. 2 medium coats is all that is required althou I start with very thin light coats and gradually build up to a final wet coat. One thing for sure is wear a respirator with plenty of ventilation or just paint outside, its nasty stuff and produces isocyanates and your lungs wont like you if you dont. Try avoiding getting any on your skin either.

Thanks for the information.
Yeah you can never be too safe with paints!
Chris

Four-to-one clear-to-activator is correct.

Before I switched back to clear lacquer, I was told by automotive paint store staff people that two-part urethane clear should not be thinned. I took them at their word, and my cars looked like they'd been freshly dipped in Karo Syrup. But on reflection, I think the store guys were giving me "real car" advice. I haven't done further research, but it's quite possible that urethane clears aren't very weather-resistant if they're thinned. I can't imagine what harm would be done by thinning it a bit. If I were to try urethane again for a model, I would thin it 1-to-4 - or even more!- with either UR40 or plain old lacquer thinner.

I screwed up one the the cars I attempted, so after several weeks I tried to strip the clear. I first tried CSC - no effect. Then I tried Oven Off. No effect. Then I tried DOT brake fluid. After about a week, some areas had loosened but most of the clearcoat was still intact. In the end I was unsuccessful, and ended up throwing away the car.

I also acquired a nagging and painful cough while I was using urethanes. When I started using a pro respirator, it stopped, and I have been fine ever since. (I still spray one-part automotive urethane color coats [aka bases, aka touch-up paint]. But I don't open the jar unless I'm wearing the respirator.)

I hope you have better luck with urethane clearcoat than I did.

Ddms

I dont know what activator you have, (there are 4 made for 7779s, each is for a different specific temperature range) but dont thin it. Unlike many other Dupont clear coats, 7779 doesnt have a reducer. The activator is the reducing agent itself. If you go beyond the 4:1 ratio, the curing properties of the clear will be upset and you might end up with fogging or a paintjob that is very fragile and even take forever to dry. While all these precautions might be over-kill for a model, due to the cost of the paints and my time into the model itself, I wont experiment. I have had no problems clearing with an airbrush (mine is a Passache VL) due to viscosity.

I dont know what activator you have, (there are 4 made for 7779s, each is for a different specific temperature range) but dont thin it.
The automotive paint store guy marked my clearcoat bottle HC2300. He wrote "hardner" on the bottle of activator.

Unlike many other Dupont clear coats, 7779 doesnt have a reducer. The activator is the reducing agent itself.
Well, the "hardner" didn't reduce the HC2300 by much. The clear coat was still way too thick for my taste. (My activator has since thickened beyond usefulness, and I've tossed it.)

If you go beyond the 4:1 ratio, the curing properties of the clear will be upset and you might end up with fogging or a paintjob that is very fragile and even take forever to dry.
Sounds plausible. So much for my half-baked theory!

While all these precautions might be over-kill for a model, due to the cost of the paints and my time into the model itself, I wont experiment.
I won't use my 2-part urethane clear again unless it can be thinned. I really don't like the extremely glossy "dipped" look, at least not on old race cars. One of these days I'll run some experiments on non-critical surfaces.

In the meantime, I'll stick with my favorite combination, Tamiya TS13 over Dupont Chromabase.

Ddms