O
Outlaw
Is there a rating on the quality of a chemical bond (application window) over mechanical bond (sanding/scuffing between coats after expired recoat window)?
crashtech
Combo Man & Mod
It gets pretty complicated. If you start reading about the science of adhesion your head will spin. The way I understand it, there isn't actually any chemical adhesion involved, it is mechanical and something called "diffusive adhesion," where the tails of unreacted polymers get tangled up before the cure, resulting in an ultra-thin layer of interlocked molecules. The second thing is what you get when the epoxy is inside the recoat window. If it's not, then you get mechanical adhesion.
O
Outlaw
Thanks Crash, sounds more complicated than I expected.
This is one of those questions you see a lot and you get all type of answers, with mostly people trying to apply common sense to the question, sometimes in chemicals common sense don't apply.
Test from years ago with an adhesion tester proves the following:
To keep it simple we will use the epoxy.
Single stage applied over epoxy that had one coat and sat two hours.
Single stage applied over epoxy, that sat 24 hours at 85 degrees.
Single stage over epoxy that sat 30 days and one panel scuff with 400, another wit 800 and another with 1000.
The tests were full adhesion on all panels with no readable difference.
Base coats would very as far as wet on wet as some bases have better adhesion the others, that is why when people call about using epoxy as a sealer I ask color and brand of base as well as temp and give different answers, for wet on wet.
Test from years ago with an adhesion tester proves the following:
To keep it simple we will use the epoxy.
Single stage applied over epoxy that had one coat and sat two hours.
Single stage applied over epoxy, that sat 24 hours at 85 degrees.
Single stage over epoxy that sat 30 days and one panel scuff with 400, another wit 800 and another with 1000.
The tests were full adhesion on all panels with no readable difference.
Base coats would very as far as wet on wet as some bases have better adhesion the others, that is why when people call about using epoxy as a sealer I ask color and brand of base as well as temp and give different answers, for wet on wet.
crashtech
Combo Man & Mod
From what I have seen, knocking the top layer off of the epoxy that is still less than a couple months old might be doing something more than just enabling mechanical adhesion, it almost seems to be exposing a fresh layer that is still capable of grabbing onto the new layer of paint better than what just a sand scratch alone would do.