Body filler in the hot weather.

[fishnjim]

Since I did polymer chemistry/eng'g my whole career, I was unwittingly frustrated, ie, I know better, on my small body work job this week becoming a prolonged waste of time in the 95+F garage.   So here's some tips to improve your chance of success, if you don't have an A/C-ed shop.   [I use this technique for my rod building finish, so I don't know why I just 'discovered" it for filler.  Dah!]
1. Ingredients: Start with a fresh can of filler and cream hardener, putty, and store in refrig (below 30C/86F) according to the MSDS sheet.  (I keep my rod making epoxy glues/finishes in an old spare refrig.   I store epoxy in freezer.)   It's difficult to get fresh so go where they supply the body shops and only buy what you will use quickly*.   I don't use much, a quart lasts me a long time, because I only use sparingly as you should by controlling metal work to within <1/16".   Catalyst says 3 months shelf life.   It goes bad faster than filler, just sitting out, so get a fresh tube at least twice a year.
2.tools:
a) Get yourself a small ounce or gram scale - I got some at the chinese take out for under $10 ea.  Just make sure they're somewhat accurate?repeatable.   Weigh something known.
b) Get some (100 ml) tri corner disposable beakers from ebay or amazon.  Mix in small batches.
c) Get a few hobby syringes.   I have an assortment, but 1-2 ml is ample for this.
3. Procedure: Take materials out before hand to warm up.  Weigh out the filler into the tared beaker.   Then weigh add the hardener from the syringe.(Pull plunger and fill from tube into plunger end.  Flush syringe with min. spirits when through.)   Excess can go back in the tube(not flush!), but take what you need to avoid contamination.   You can store the filled syringe in refrig probably as well but it's not closed that way so use up fast.
Mix thoroughly and quickly 15 - 20 seconds with a popsicle stick or similar and quickly dump onto a flat container - I use an old spare vent glass, it cleans easily.  Cardboard will do, but you have to throw away each time.   Don't let mix sit in the beaker, it'll melt beaker.   Spread quickly.   Once remainder is set, scrape off hardened and repeat as needed.
I'm constructing a dose table, but for now, 1.02 oz filler, I used 0.08 oz hardener and got 1 minute pot time at 80F.   It was long enough to do the job.   If you don't add enough cat trying to increase pot, it'll be sticky and won't sand.   It's too variable to be consistent and judge amount from eye.
My filler was old, catalyst new, so I'll be improving on this with the new can, but I'm almost finished with this last job, and will report the new data later.   Label says 5 minute pot time, but that's at room temp.   {Rule o thumb - rates double every 10 degree C.}
* - Filler will slowly polymerize over time in the can as the antioxidant/inhibitor is consumed, and then it takes less catalyst to do the same job.   So if you follow the normal cat amount, it sets up faster.   Plus the liquids separate from the solids, if stored warm, and drain to bottom of the can, so mix the can thoroughly before use for consistent pot life.   Keeping cold will keep it stiff so it won't separate as fast.