I`m repainting a 72/240Z at the moment, the car was stripped to bare metal, 2 coats of epoxy primer and now I'm filling with UPOL Dolphine One Fill before the high build primer goes on. Seems like great stuff, identical to Evercoat Rage.
I've been reading a lot of previous threads in the archives of this forum and now I'm concerned about shrinkage if the filler doesn't get some real summer heat before paint.

It's January in southern Ontario, the temp outside is -2 F, my shop is a bit on the cool side, normally 60F and when I'm priming/painting I can get it up to 75F but it takes a good 6hrs, the humidity is very low, approx 30-40%.

Can I help it along with the careful use of a heat gun or ... am I over thinking this?
Thanks,
Chris

Well, I for one, don't think you are overthinking this..... even when I was young, broke, and not the brightest bulb in the lot I would use a few quartz electric heaters in my one car garages. I would do filler in sections and keep the heaters on those sections for a few days, then move on to another section. Those heaters heat objects rather than just the air so I could keep them on low. I'm not hot (wow, did I just say that ) on doing it with heat guns as that is just too localized. I don't mind using heat guns to help "kick" a reaction but that's about it. An obvious way to reduce shrinkage is to do your best metal work to reduce the amount of fillers you are using. If you are using a high build filler, same there, if a lot goes on....it should end up sanded off and on the floor......
The other guys will have some tips here.....

I am of the opinion that the shrinkage of most all of the products we use takes place over Time, Curing continues For quit a while even when cold, Is it best to keep temps up? you bet! but will these products fully cure in a couple days? No.

Example:
Mix up a Batch of Any epoxy and just leave it in a Mixing cup and watch it!
It will continue to shrink and get hard UNEVENLY for Months! I have kept a few Hockey pucks around for over a year and the bottom was still soft while the Top was rock hard and it continued to shrink like this for over a year.
Its always Best to keep all of these products Coating's thicknesses to the Bare minimum when applying to avoid showing shrinkage!

Hi build primers do the same but don't shrink as much, Fillers do too and will shrink a little Some are much worse than others.
How much and for how long always depends on the thickness of that coating Temperatures, Sun light and Time they all play their part.
Its just one of the many evils in this game.

Thanks guys, probably the thickest the filler is anywhere on the car is 1/4" and it's the main bodyline on the rear quarters. Both those areas had metal repairs yrs ago and I stripped off 1/2" bog. I've worked the bodyline some with H&D but can't get away without a 1/4" of filler, all other areas are much less than that.

I have seen 20 yr old filler that was almost an inch thick
that still looked perfect before I started sanding into it.
My standard is no more than 1/4", but sometimes I wonder
if it makes that much of a difference.

go to your local hardware store and pick up some heat lamp bulbs and the clamp on lamp holders. make yourself a stand and your good . be careful with the heat lamps, you just want to get the area WARM not scorched.
Jay D.