What's the point of the epoxy "window"?

5

59mga

It's my understanding that epoxy primer does not chemically bond with anything put over top of it. Maybe that's not true.....but that's what I've read. If that's the case.....why bother with the 7 day "window" at all? Shouldn't we just always scuff and then shoot whatever is going over the epoxy primer to create a better mechanical bond?
 
The open coat is part of the cure and there is no such thing as fast and being top notch in any product.
There are epoxies out there that have a 2 day window so you can sand if you want.
Full cure on the SPI epoxy is 30-90 days, depending on a lot of factors but its not for everyone.
 
To answer your question what is the point, well if nothing else it save the shops a whole bunch of sanding when they apply filler or primer over the epoxy.
In a restoration, could be 20-100 hours depending on the restro. So say an average hour rate charge of $50 an hour, this is $1200 to 5000 savings.

By the way, if there was no chemical bond, we would not say you MUST wait 48 hours or longer before using a polyester primer, instead of 4-12 for a 2K primer.
Reason is not important but has to do with acetone and mils of product and wicking.
 
shine;n70804 said:
where did you read this ?
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Take your pick.

But about polyester. 48 hr window before applying polyester? Did not know this. But as slow as I work shouldn't be an issue.
 
Lizer;n70811 said:
Take your pick.

But about polyester. 48 hr window before applying polyester? Did not know this. But as slow as I work shouldn't be an issue.
Click to expand...

Me neither Josh. We learn something new every day! :))
 
So if you go over the epoxy within the window (i.e. without scuffing), is it purely a time-saving thing (not having to sand)? Or is there some sort of adhesion advantage, compared to sanding after the window? I am going to be laying the epoxy down and then applying filler well after the window has completed.
 
You won't have any problems applying filler over cured and sanded epoxy-the adhesion will be just fine. Although it is better if applied within the recoat window-you'll never be able to separate that bond in any kind of destructive test.
 
And if you need further validation watch the YouTube video with SPI Epoxy, the guy runs it through it's paces and it never failed enen in the slightest bit. You can put your trust in SPI. The truck I'm redoing is completly loaded with SPI epoxy and will be painted with SPI base and clear. I've been doing this work for 30+yrs and it is hands down the best.
 
shine;n70804 said:
where did you read this ?
Click to expand...

It's all over some of the more popular forums. Seems like someone "respected" posts something then it gets repeated as gospel and more and more people repeat it so they can seem to really know what they are talking about. Irregardless of whether it's actually true. Painting your own car makes you an instant expert.;) Welcome to the Internet I guess. When I took the Mercedes Benz collision repair course in order to get certified by M-B way back in 1995 (wish I could go back as I was still a young pup of 22...sheesh I'm getting old::D) they were the first ones who were requiring epoxy over bare metal and underneath body filler. They referred to it as a "chemical bond". So I've always thought of it as that. Perhaps adhesive bond is technically more correct but who knows.
 
There's a lot more OEM's specifying epoxy primer before fillers these days, Ford has also jumped on board with repair procedures for their new aluminum F150. The corrosion repairs I've done over the years on aluminum hoods in this area of road salt hell have held up really well-I use epoxy primer on the bare metal.
 
Chris, I will never for get when Mercedes came out in late 70's or early 80's (don't remember) and said all warranty work with bodyfiller had to be applied over epoxy, the Glasuit would work (before they were BASF) PPG went ballistic! Cant be done and will not work!!! As they lost their high end shops, then all of a sudden, yes this is the way to do it. Re internet, I spend a lot of time explaining that my epoxy has no acid and body filler has no acid and neither will stick 100% to an acid film. You have to wonder where people come up with this crap.
 
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