Blocking with 2k primer vs blocking with epoxy only

P

projectzj

Gentlemen-
I hope I'm not opening a can of worms here...but:

What are the pros and cons to blocking out with 2k Regular/HighBuild/Turbo urethanes before basecoat (over an epoxy base of course) VERSUS just blocking out with layers of epoxy only?

I've read on here that SPI epoxy blocks out just fine. So is the only real benefit of a 2k the extra thickness you lay down with each coat?

I'm trying to decide which route to go and would greatly appreciate your inputs.
 
The 2K sands out easily a lot quicker and does fill better but
the epoxy gives much better adhesion.
Since I switched to a epoxy sealer coat for my bumpers, (new & old)
before paint,
I've seen a huge difference in less road rash.
 
I'm doing a '53 chevy truck and initially planned on using shine's method of epoxy only before base. However with the amount of real estate and the need to block everything, my arms just couldn't have block sanded the epoxy on the whole truck, so I primed with epoxy then went to 2K high build. The high build was great and sands so easy. I'll seal with epoxy before base.
 
i did 6 coats of epoxy on the 57 corvette . 2 at a time and blocked each round . if one is bad enough i will go to slicksand .
 
Shine:
How long do you usually wait for epoxy before sanding?
(I have sanded in 24 hrs but find 48 is much, much better)
 
during summer here i can epoxy in the am and sand the next day . just depends on temp.
i never get in a hurry. i judge cure time by how i want it to sand. i dont want a surface that sands real easy .
 
I have lots of real estate to cover and none of the panels are really all that straight so I have some work ahead of me. Shine why do you prefer slicksand over SPI 2k high build (which is uretane based right?)? I've never used slicksand before, maybe I should give it a shot.
 
i dont use urethane primer at all . slicksand is polyester and 2 coats will likely give you enough build to block.
 
Hey Shine, (and Barry of course):
i did 6 coats of epoxy on the 57 corvette . 2 at a time and blocked each round . if one is bad enough i will go to slicksand .
I’m finish blocking in epoxy. Should I shoot a fresh coat of reduced epoxy prior to my base, or can i spray base over the blocked epoxy? Similarly, on areas like door jams that were epoxied 6 months ago, can I scuff and spray base, or recoat with epoxy before base? The book says to sand with 180, but I don’t think want to do that. Red scuff pad?
 
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SPI epoxy is suppose to be good to paint over within 7 days without resanding.
(I prefer to go over it with a scotchbrite pad if it's more than a couple days old)
 
anyone have adhesion test data on 180 vs 400 grit vs scuffing on old epoxy?
 
Reduced epoxy is the way to go before base.

If your doing reduced epoxy in preparation for base then you dont want to go with 180. Just hit it with a hand pad and some 320-600, maroon scotch brite everything else that doesnt get sanded, or hit it all with a maroon scotch brite. I think an actual sanding grit scratch is better personally but its all personal preference I think.

I like reducing 25%, spraying one coat, then spraying base in a couple hours if your temps are good. Remember as the tech manual states, if you reduce the epoxy the cure time speeds up, so between 2 - 18 hours it says you need base on to not require sanding.
 
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