Urethane drying/hardening time?

I'm in the process of painting the rear end, and other undercarriage pieces with single-stage urethane. I've been following the directions given me, to use 8 parts paint, 4 parts reducer, and 1 part hardener. OK so far. I painted a few pieces 3 days ago, and although they seem throughly dry, I can scratch it with a fingernail. It's been sunny, with temps in the 70's. I know it will never be as hard as the powder coating on the frame, but it seems to me that it ought to be harder than spray can paint. How hard can I expect this paint to get? And, how much time should I give it before working with the items to put them back together? Thanks for any advice you can offer

Drying times vary between manufacturers, the speed of the hardener, and other factors....but I can tell you this:

With the brand I use, the paint is dry enough to sand and buff in two days, but according to the maufacturer, is not thoroughly cured for 8 days, at normal temperatures.

Also, just as a side note, when the temperature of the surface (and paint) falls below 48 degrees, the paint literally stops the curing process....REALLY!!!!!!!!!!

Since your temps are different, and you are using a 8/4/1 mix, I'd stick with 8-10 days at temps above 70 degrees if you used a medium reducer instead of a slow one.


Bill S.

Thanks guys. Sounds like I'm OK then. Just have to give it time. Like I said, temps have been around 70 during the daytime. The parts are inside a very well insulated garage, but still, the temps are geting into the 30's at night. So, I'll just give it time to cure. Thanks again. I sure appreciate the help