The great thing about the epoxy--pot life is loooong. Once it's mixed up, it's good for several days. I have gone back 4 days later I think it was, and the epoxy was a lot thicker and didn't spray well, so I pitched it. It's not like a 2k primer or poly primer that sets up in the gun in 30-60 min. Hell there's a 30 minute flash time between coats of epoxy, which means sometimes it may sit in my gun for an hour or more.
So to your concern with epoxy, if you have extra, pour it into a mixing cup and put foil on the top. It's good in there for several days. You can use this time to prep another panel or get something else ready to spray.
I've been pretty good, or lucky, about accurately guessing about how much I need whether it's spraying a single panel or the entire car with epoxy so I usually don't end up with much left over, if any. But it's nice to have several things ready to go at the same time, so once you have sprayed what you really wanted to spray, you can use your leftover to spray on the other panels that are prepped.
The other thing I do is keep a log in the shop where I write down how much I used to spray a certain panel....ie '3 coats epoxy on rear valance, 3 ounces.' Just making numbers up there. Makes it easy to refer back...then I can say well if I used 3 ounces on that, and this new panel I want to spray is roughly about twice as big, I had better mix up about twice as much.
The 2k primers have more mil build than epoxy, sand a little easier, don't require an induction time, and subsequent coats can be shot with much shorter flash times. Basically easier and faster to use. These pro's like to go on and on about using epoxy as a one stop shop for building and filling, I just don't think it's practical advice for an amateur. My panels require a little more help than what any of these guys' will.
People don't like the 2ks because of their tendency for shrinkage which you don't get with epoxy. I can mostly avoid this since I'm also using SPI's 2k which isn't talc-based and uses a different solids substrate that doesn't shrink as as bad. But just to be clear, epoxy and 2k can both be used on the same car...I've been doing 2 coats epoxy on bare metal, do my filler work over that. Then I put another 1-2 coats epoxy over that so the filler can soak it up, and because I've sanded to bare in some spots most likely. Then 2k primer for build and imperfections, block it down, I ended mine with 400 wet, then I went over the entire car once more with epoxy as a 'seal' coat basically to hit any small bare metal spots if I hit an edge or something while sanding, and to give the car a uniform color. Then, because there might be some spots with dust nibs or maybe a little bit of peel, I go 600 wet over the final epoxy coat before base.
Last edited by Lizer; 08-25-2013 at 10:19 PM.