Waiting time for scuff/sanding of epoxy?

B

BFLIT

I have a question about sanding after an epoxy primer is sprayed. The tech sheets say to sand with 180 grit if you are going to spray on fill primer after seven days. I plan on doing that but I was just wondering why you need to do that? I don't need a real detailed explanation. I'm not planning on getting a degree in chemistry but I am curious and wonder if painting before the seven days is better as far as adhesion goes as opposed to letting the piece sit for a week then sanding.

BFLIT
 
After 7 days, sand with 180 and spray another coat of epoxy, then fill primer. Before 7 days, spray your fill primer directly over epoxy with no sanding. At least, that's how I understand it.
 
Revolver;31686 said:
After 7 days, sand with 180 and spray another coat of epoxy, then fill primer. Before 7 days, spray your fill primer directly over epoxy with no sanding. At least, that's how I understand it.
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That's how I see it, too......and I think the 7 days is pushing it.....no more than 4 days at our shop, just to be sure we get intercoat adhesion, but I also know people use the 7 day window and get along just fine
 
The recoat window is so dependent on temperature. In the heat of summer, I've seen early adhesion problems start as soon as 72 hours. By early adhesion meaning seeing tearing or peeling while sanding filler that is still easy to work, within 30 min of applying. A quick sanding with 180 or even a red Scotchbrite totally eliminated that problem for me. So he non-sanding recoat window in my shop has become 72 hours, though I am sure more epoxy could go on epoxy even over 7 days with no issues in most cases. Sanding is just extra insurance.

As you can see, recoat window is not a cut and dried thing.
 
I am beginning to see how important temperature is. I am amazed at how different the metal temp is compared to the air temp. I bought an infrared temp meter and it works great. as cooler weather is setting in I'll be using it alot.
 
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