Epoxy then Filler - Quick Question on Glossy Epoxy

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Been reading threads for hours trying to find the exact right answer to this:

I shot 2 coats of white epoxy last night over a fiberglass tub for a vintage airstream and it seems to have cured very nicely. Its sitting in the sun for a few hours now. I have a couple areas that need some fill tonight and I've read you can go right over the epoxy with filler. That said - the white epoxy is so nice and glossy it makes me nervous. As it just takes a few minutes to scratch it up in those areas - do I get a better filler adhesion with a 80-180 scratch or do I actually get better adhesion with that shiny surface (and of course I just couldn't resist touching it with my hands!) ?
 
IMO there's no adhesion advantages to scratching the epoxy when it's this fresh. Apply it and don't worry.


An overnight cure of the epoxy primer and direct application of filler is the best scenario IMO, the bond is optimum from what I see.
 
You should be fine, however, we NEVER put anything over anything without scuffing in some way except for the finish coats just to give mechanical adhesion also
 
Well it sounds like I'll be fine either way then - thanks guys. Love weekends when I get to use my spray guns !!
 
You should try it on a test panel to see for yourself. Within 48-72 hours, there really is no sanding required. I am extremely picky about what I see when sanding. In hot summer weather, I have noticed the beginnings of adhesion issues with filler on unsanded epoxy at about the 72 hour mark, so after that we scuff sand before filler.
 
I have always been told and figured that it couldn't hurt to scuff. I always scuff whether its needed or not it only takes a second and could never hurt....
 
I may have just double posted :(

I'm going to use 48 hours based on what i am hearing and reading. More than 48 I will scuff.

Carrying on this question maybe someone would answer this - if I lay 2 thick coats of epoxy and need just a few small areas where filler goes (less than dime sized spots less than 1/32 inch deep) - do I need to reapply or spot in epoxy over that filler or can I just go to 2K over the filler on that small of area and then epoxy seal coat?

Thanks - Jake
 
2K or epoxy would work fine, you're going to sand the spots again before sealer right?
 
Yes that's correct Bob - I would plan put a little filler into the small areas, sand, then apply 2K. Sand the whole thing and then seal again with reduced epoxy before base - although my white epoxy seems plenty thin that it worries me about runs to reduce it more. Sound right?
 
This article was on another paint forum:
Using body filler, by Reed Overson Last updated on September 28, 2013

Reed Overson lives in Bismarck, North Dakota, and has been a bodyman, painter, sales rep, and technical rep for thirty years.

Reed used to work as a technical sales rep for the company that makes Rage filler, and knows the chemists that developed the resin for it.

The following article contains some of Reed's thoughts on using body filler.
The resin used in Rage and other body fillers is fiberglass (polyester) resin. Today's resin technology makes the adhesion of these new resins as good as or better than most epoxy adhesives. They are designed to really stick. Also, they are somewhat flexible when used properly.

Most, or probably all, filler manufacturers design and recommend them to be used over clean and prepped (sanded with coarse 36-grit), rust-free (sandblasted), dry (free from moisture), bare metal. They will stick to epoxy primers with mechanical adhesion. Body fillers do not chemically bond with epoxies. If you put filler over epoxy primer, it has to be fully cured, with no solvents such as thinner or reducer left in the primer, and still should be sanded with a coarse grit and cleaned. In other words, using epoxy primer under filler is a wasted step that may or may not cause adhesion problems later on.

- - - Updated - - -

This article was on another paint forum:
Using body filler, by Reed Overson Last updated on September 28, 2013

Reed Overson lives in Bismarck, North Dakota, and has been a bodyman, painter, sales rep, and technical rep for thirty years.

Reed used to work as a technical sales rep for the company that makes Rage filler, and knows the chemists that developed the resin for it.

The following article contains some of Reed's thoughts on using body filler.
The resin used in Rage and other body fillers is fiberglass (polyester) resin. Today's resin technology makes the adhesion of these new resins as good as or better than most epoxy adhesives. They are designed to really stick. Also, they are somewhat flexible when used properly.

Most, or probably all, filler manufacturers design and recommend them to be used over clean and prepped (sanded with coarse 36-grit), rust-free (sandblasted), dry (free from moisture), bare metal. They will stick to epoxy primers with mechanical adhesion. Body fillers do not chemically bond with epoxies. If you put filler over epoxy primer, it has to be fully cured, with no solvents such as thinner or reducer left in the primer, and still should be sanded with a coarse grit and cleaned. In other words, using epoxy primer under filler is a wasted step that may or may not cause adhesion problems later on.
 
I sort of agree with everything he says with the epoxies we have used....except SPI...it is major different...however, we always scratch before applying anything, just to be sure...
 
bob;35158 said:
This article was on another paint forum:
Using body filler, by Reed Overson Last updated on September 28, 2013

Reed Overson has been a bodyman, painter, sales rep, and technical rep for thirty years.

Most, or probably all, filler manufacturers design and recommend them to be used over clean and prepped (sanded with coarse 36-grit), rust-free (sandblasted), dry (free from moisture), bare metal.
Click to expand...

That sounds like what I find on some old cars that I strip the thirty plus year old paint jobs off of, and it really irritates me to find those deep gouges.
Maybe he meant that he was a bodyman, rep thirty years ago, instead of for thirty years.
http://www.fiberlay.com/upload/techd-06104011210-RAGE GOLD TDS.pdf
 
bob;35158 said:
This article was on another paint forum:
Using body filler, by Reed Overson Last updated on September 28, 2013 In other words, using epoxy primer under filler is a wasted step that may or may not cause adhesion problems later on.
Click to expand...

Filler gets used every day without the use of epoxy primer-true!, there's some epoxy primers that are not designed to be used under filler, some people have never used epoxy primer of any kind... There's some brands of epoxy primers that shouldn't be used for anything IMO. Do what you want-it's a free country LOL When auto manufacturer's spec epoxy primer under filler work for warranty I guess that means nothing? I've been testing the advantages of the proceedure in the harshest road salt area in the country since the late 80's-and to say there's no advantages or a potential cause of adhesion failure is so far from real world results it's almost laughable.
 
Reed Overson is living in the past, but then again so are most of the major paint companies' tech sheets.
 
Filler over SPI epoxy at the optimum time within the epoxy's re-coat window provides bond strength that ends up being stronger than both of the materials, no scratching needed. After full cure the two products will not seperate. Destructive tests show the filler will always fracture and may even chunk off but a layer at the bond line will always remain.
 
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