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Epoxy Primer cure time

29K views 26 replies 7 participants last post by  67Elcamino 
#1 · (Edited)
Just wanted to ask for any opinions on this.
Yesterday here in California It was scheduled to rain, but to my surprise at about noon the weather hit about 70 degrees and sunny. I was working on my 64 Cadillac doors that I had previously stripped down to bare metal, applied epoxy, and bondo and was blocking the doors getting them as straight as possible. While block sanding about 40% of the door had eposed metal again. I have leaving exposed metal bare for over a week, even if it was stored in a dry place.
I got anxious and decided to shoot SPI Epoxy over the entire door panel to seal from moisture. As soon as I shot two heavy coats of SPI the weather quickly started dropping.. (to a chili 66, then a freezing cold 60-62 degrees) I quickly grabbed the doors and put them in the garage.. 20 minutes later it begins poring rain (emergency here in SoCal). 8 hours later I check on the epoxy and still very wet, checked again this morning at 7:00 (19 hours after I sprayed) and the doors are still tacky..
Should I be worried about how long the doors are taking to dry? Sorry if this is a stupid question, but will the Epoxy lose its strength if it doesn't dry within the timeframe is was intended to dry?
I still consider myself an amateur in this hobby, but I consider myself a pretty quick learner. Usually because I overanalyze everything.. and always dying to know the 'hows' and 'whys' of it all..
Interesting thing I notice is how much a slight change of weather effects the paints cure time. Seems like not just hours but in some cases days..
 

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#2 ·
You need to have the metal above 60 degrees to get a cure..Some heat lamps or electric heaters can do the trick. It is a mistake to go by air temp as the metal can be cold. One of the laser thermometers will be very helpful in this case..

Sam
 
#3 ·
epoxy will go dormant at around 55 degrees. does not like humidity either but after this long at above 60 it should have kicked. it you heat them up and it does not cure out then i would check my mix .
 
#5 ·
as long as it cures. over night is about as long as it has taken . if the temp is up for the first few hours you will see it kick off. not ready to sand but it should kick dry to the touch .
 
#11 ·
Yes! it passed the fingernail test a day and a half later. Shine, I do notice that SPI epoxy dries a bit glossier than other epoxies Ive used (not that i've used many) My concern is adhesion of the top coat. Im not quite confident that I can use it as a sealer because of this.

Any insight as to why?
 
#13 ·
its a great sealer ,I usually sand it any ways but it can be used unsanded . For instance on an aftermarket hood when you get done sanding that crap primer off and its almost all bare metal you can reduce it about 25% and spray a thin coat and go right to paint .from what I understand it can be reduced up to 40%.... its a very versatile sealer also....
 
#15 ·
Straight from Barry at SPI ....it works very well and never once had an issue with the base lifting the epoxy ..even doing a wet on wet...I admit being a little leary about over reducing and I never went as far as 40%, 20% is pretty thin and works good...in this kind of bare metal to paint situation you run into doing collision work where time is everything...
 
#16 · (Edited)
i have experienced it first hand. thin coat to kill black on edge of a two tone. shot the epoxy to just give an even color. shot the silver base and lifted the epoxy.
the silver below the belt line lifted by the second coat.
 
#21 ·
ok,if shot over fresh paint I can see how that might happen but not to metal. I've done this many times over metal and it works well every time.it's standard procedure when I paint an aftermarket panel now..spray reduced epoxy over bare metal , then go right to paint, no waiting or sanding. if it was un reduced it would take time to cure and have to be sanded...I'll keep that in mind though on my "Not" to do list...
 
#18 ·
The biggest thing is if the substrate that the epoxy is sprayed over is scuffed-"sanded" well.

If the epoxy (or any primer) is sprayed like that black area then it "falls" onto where the silver is painted but the whole silver area isn't primed, then you have an area that is like a "blend" where the primer is going from full coverage, and full solvent resistance down to nothing on the edge, so it's going from full solvent resistance to no solvent resistance. If that area of the substrate where it has "blended" off to nothing isn't sanded well the solvents from the next product applied are going to get under the edge of the epoxy lifting or "wrinkling" it.

I have done it too, remember it well, created a bunch of un-needed work. But as a rep I saw it so many times, it was drilled into my head. I never made that mistake again! We think "I'll be needing to sand that later" so we don't sand it as well as we normally would. And it comes back to bite us.

Brian
 
#19 ·
Martin, are you talking about the dry edge above the center of the fan? If so, I agree. So many people don't sand that off and it does lift. It doesn't get into the teeth and sits on top and so when solvent hits it, BAM, it lifts. Some people don't see it as a problem as long as what it's sitting on is sanded/scuffed. I sand it out anyways. It doesn't hurt to do so.
 
#22 ·
the panel was taped off then black was shot. reversed taped then shot color stripes. last thing shot was silver so the fresh coat of epoxy was shot to even the color and as a sealer. i shot a thin coat and by the second coat of silver it lifted. not just over the color but even down low. the coat of epoxy was just not solid enough to prevent solvents from getting through. lesson learned .

in the quote it should say the silver lifted the epoxy .
 
#23 ·
I just shot another section of the car with Epoxy. It is about 86 degrees outside and used a medium activator. I noticed it dried very fast but left an even shinier finish to it. I want to shoot a couple heavy coats of Evercoat featherfill polyester so I can blocksand. Since the Epoxy seems really glossy would it be ok to shot the polyester without scuffing?
What is the recoat window given that it was shot at 85 degrees?
Any ill effect given that it dried so quick? Does it make sense that it has a glosier finish when sprayed at a higher temperature?
 
#27 ·
Heres what I found to be my best combination. SPI epoxy over bare metal, followed by 2-3 heavy coats of contrasting color Evercoat polyester featherfill g3, then skim low spots with evercoat extreme gold filler. Let it sit for a couple weeks for shrinkage etc. apply guide coat and begin blocking. When I begin seeing the epoxy, i stop as I do not want to expose the metal. I then apply another 2 coats of featherfill, and block again until its all perfectly blocked. This technique saves me from reapplying the expensive Epoxy when I hit bare metal.
 
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