The Stovebolt Site Forums The Shop Area Paint and Body Shop Filler Or Epoxy first! Interesting Test

I finally have all of my '59 body pieces to bare metal.
Now is the time for dent removal, patching new steel and any other body work prior to final paint.
I've been fortunate with the panel patches but never have painted before... so I'm watching videos and reading a lot.
Before I even start, I discover there's quite a debate over preference in application of Epoxy Primer over bare metal, then applying any filler Vs Filler to metal first.
My Rage filler can says over metal (btw).
Of all the reading of opinions of people who have done it both ways and prefer one over an other... or state it doesn't make a difference, I hoped to find a true test of the applications.
I found this and thought it might be worth sharing.

Epoxy or NO Epoxy Under Filler

Wish me luck as I approach this aspect of my truck rebuild journey!

Jerry

I cannot argue that filler to bare metal will stick the best. But, in the end, it boils down to convenience for me. Generally, all metal parts are stripped, media blasted, etc. at one time. Now, if you don't get a protective covering on all that bare metal, you are in for some trouble. So, it gets a coat of epoxy primer. Now, many weeks/months later you are ready to apply the filler. What are you going to do, sand off all that epoxy or just scuff it up and apply the filler directly to the epoxy. A no brainer for me and I have never had a bond failure of filler over epoxy. Granted, I am not whacking my truck on the corner of a desk and if I crash it, who cares if the filler comes off...just makes it easier to repair in the long run.

Just my humble opinion. Everyone should do what makes them sleep well at night.

If you were to do a search for the number of body/paint folk who no longer use PPG DPLF epoxy, the 'test' is indicative of it's reputation for failure...

Also any prep other than sanding was not indicated.

But that's not why I go with SPI epoxy first, it's because I found rust under the filler over metal on my truck, where the filler was STILL in tack and full adhesion.

... and I'm still reading.
Good points, guys.

Caso,
I hear the filler if not covered could allow moisture to penetrate. I was just wondering if your filler was exposed for a period of time. I'm trying to envision why the rust developed.
Thanks for the tip about SPI.

In much the same manner as super heated air yields moisture in your air compressor once it hits the cool tank/piping, a mix of filler creates heat as well, and likely will experience a slight amount of condensate if the body panel is somewhat cool. Some eliminate this issue by preheating the panels with infrared heaters, some don't worry about it if the temp in the shop is well toward 100 degrees, some don't know otherwise, some don't care. A nice humid environment may play a part in adding moisture as the filler is mixed. Multiple, thinner layers of filler should minimize the issue vs. applying too thickly all at once, which generates heat nicely. Some rather have the epoxy on first to seal any moisture from the metal.

A widely debated topic, which will never have only one accepted answer. I will say I have seen the video before as it has been out for quite some time, and I have also heard there were prep inconsistencies. I would have rather also seen a head to head using all the major epoxies to see if it was just a DPLF issue. If House of Kolor still made their EP-2 formula with zinc chromate (thanks EPA) I would stack it against anything. That was some good schtuff.

Very happy here with DPLF. Key is to really adhere to induction which is a nuance to this primer. I might try SPI someday, but haven't found the need yet. The idea of using rage gold on bare metal is good news for everyone since even if you used epoxy, or etching primer to preserve the metal after blasting, you will sand some of it off during the process and this negates the need to re-apply primer before fixing those areas. Its good to see tests performed by a seasoned professional to disprove the need to always keep primer between the metal and the filler. We all win! We should beg Serge to test it with SPI. But sorry Caso, he used the primary, best selling brand to test. I know how you feel and I really would like to see him do it again with SPI. If the test was better, I would switch in a heartbeat. Lots of SW users out there would appreciate that test using Sherwin-Williams brand epoxy. But at least it was a start. Hats off!

I have had metal with filler sitting around in my shop here in Kansas for 5-8 years with no rust developing under it. Something I worry about. But, lots of hobbyists do not have a climate controlled environment, which totally explains it. My shop is 74 degrees plus/minus 2 year around. If the temperature/humidity swings are normal for North America, I can see rust occurring.

Jerry I tend towards 'hoping' the modern higher quality polyester fillers (bondo) have less talc and more high tech fillers like ceramic spheres and the like, so they are less absorptive.
My understanding is it's the talc that is the problem.
Great Bondo knows it was a lot of white filler I kept finding on my truck... and what the rust was under.
But I 'Hope' for better corporate citizens too...

So I attribute the particular spot of rust I had in mind to Roberts scenario of 'Hot Mix'.

DavidF's reasons are spot on in my book.
Soon as it's clean it's rolled brushed or sprayed.

I'm presently trying out a Black epoxy 'temporary' paint job on my 1/2 OT truck. My plan is to see how it sands down for sealer and a top coat in a year or so.


And just for perspective... The rust under filler, I'm talking about a dime size chunk of rust under a 25+ year old repair that was little more than 'surface rust'. So NOT the end of life on earth...
NOTHING like the Whole holes caused from plain old dirt caught in cab corners or cowls.