Technical Body filler over metal vs over epoxy. Interesting video

Found this video on You-Tube. Interesting test setup, what do you guys think.

 

I can't comment on if this test replicates real life situations but it does appear conclusive.

This brings me to my question. I was recently told that the reason filler is used over epoxy primer is that after the steel is cleaned it will begin to rust in hours. Therefor the best method is to prep your steel with blasting and put epoxy primer on as quickly as practical, then use filler.

I was also told that the filler will absorb moisture and cause rust between the filler and bare metal.

If I was to use filler before primer what is the best sequence to minimize and rust issues down the track.

Thanks

Steve

 

What brand epoxy?
How was the epoxy side prepped?
Was the epoxy sanded before applying filler?
How long was the epoxy allowed to cure?

Too many questions for this to be conclusive

And why 36 grit? New filler is designed to adhere to 80 grit.
Filler isn’t structural anyway. How strong does the bond need to be?

interesting vid.
Thanks.

 

I thought about the video a bit more. The filler stuck equally as well to the metal as the epoxy. The epoxy stuck equally as well to the metal as the filler. The failure point was the epoxy. There has to be a failure point somewhere.

I guess that answers my question, prep metal, epoxy, let cure and then use filler.
Please correct me if I am wrong.

Steve

 

Just don’t expect it to hold up to an impact wrench.
After painting, leave the impact for wheel removal

 

I've been applying filler over metal since I started in 94. I have a car I painted for my dad in 97 with filler over metal with no issues at all 25 years later. I worked in a restoration shop that we applied filler over ppg epoxy, no issues there either. I think it's a matter of preference by the guy doing it. Either way, modern fillers over 80 bites like crazy. No need for 36.

 

This debate was raging in the early 70's when I learned body work from a couple old lead guys, one used filler over steel just like they did the lead the other said times are changing time to use the modern method filler over lacquer primer..................................

 

Interesting video, however, I’ll agree with Anthony about the various question of the epoxy side prep/application/etc. I’d also ask HSF respectfully about how humid is it in Lodi Ca? Anthony and I are in similar climates, where if the humidity gets down around 60%, we think it’s dry. Lol. I’m not questioning if the filler will adhere to bare metal, heck I was raised up to grind with 36 grit or sometimes even 24. Definitely not necessary now with improved fillers. As I said, that’s a very interesting video and thanks for sharing it. I guess I’ll keep on locking out potential moisture before filler by way of epoxy.

 

Just about everything that I have seen rust under filler had holes in the metal behind the filler including my own truck. Remembering that back in the drill a hole to use a dent puller with a screw days they didn't weld up the holes after they got the dent out close enough to spread the filler on. Some guys even claimed that the holes helped the filler hold. I'd think that most of the rust issues come from some sort of hole in the metal behind the filler.

 

If the epoxy isn’t fully cured, the application of a product, especially a 2 part product, can cause the epoxy to fail.
I’ve seen it soften up and release filler/primer.

 

When was the last time any of you saw 1/4" or thinner plastic fall off? If you read the instructions for applying plastic over epoxy, the window is not very long. I don't live in a humid climate so I can get away with lots of procedures that those of you in a humid area can't . I don't have an answer. ???

 

I have never used filler over epoxy. I live in Ks like WFO guy. We don't have issues with moisture between the bare metal and topcoats. I've heard all about moisture getting between metal and filler. I have never seen it . I have seen contaminated metal with filler over it. Like bad metal surface with filler over it. But I see no way for moisture to get between good metal and filler unless the back side of the metal was junk with pinholes in it or something. I only put filler over properly prepared metal. I have ground filler out of cars and seen rust underneath. But I believe it was there when they slathered the filler on. Or the filler was cracked letting moisture in between the filler and metal. I don't think I would have a problem with filler over epoxy that was put over properly cleaned and prepped metal. But it just seems that the epoxy is just one more coat of material to cause a problem down the road. JMO. Your results WILL vary.

 

I tend to work an area at a time. After blasting, welding, metal prepping I usually coat with epoxy to prevent any further rust incursion while I move on to the next area of concern. So in the end, a lot of time has elapsed, most is epoxy coated and needs to be abraded with a coarse paper before applying filler if needed. Some areas don't get epoxy if being body filled immediately. It is just a matter of maintaining adhesion in between processes.
I never noticed any difference over bare metal or epoxy.

Just to add: In the video the epoxy was the fail point. Fully cured epoxy is pretty dang solid in my experience.

 

I use PPG DP epoxy regularly. I don’t think it’s as good now as it was before they took the lead out of it. I’ve had a couple instances where it has shrunk and pulled loose in tight inside corners. I never had that issue with the old DP. Granted, it was partly my fault for getting it too heavy in the corners, but as I said, you didn’t used to have to give it a thought with the old stuff.

 

WELL..FOR ONE ..NOT VERY FAIR TEST..ONE SIDE SANDED WITH 220 GRIT..OTHER WITH 36 GRIT...
was taught to 80 grit...epoxy...then do your bodywork.....epoxy will protect the metal ..bodyfiller can take on moisture... and chemical bond will be just as strong and metal protected by epoxy...have used dtm in past...direct to metal highbuild...it has rust inhibitors and sticks amazing..light sand and do filler work if necc......less filler the better..

 

epoxy, paint, primer etc is all softer than the filler plastic. of course it will fail first. if the same test was done on a finished surface the paint or primer would fail before the filler, no matter which was applied first. think chain-weakest link.
I think the test proved that it sticks just as well to the primer as it did the bare metal. so do what has worked for you and your comfortable enough.

 

I'd like to thank Bcap55 for the video as it has caused a lot of "food for thought", and I thought it was a pretty neat video. There will always be variations in results based on the products used and the method of application. It would take a long time to cover all the variables and compare them. As far as grass roots testing goes, I think applying the filler either way will produce a satisfactory result if done properly, but I tend to think direct application of filler to metal is probably somewhat better. What do I base that on........I dunno

 

Thanks for posting this.

 

Another timely post. I think the test was fairly done and presented. There are many variables not addressed but it seemed like a good representation of what many folks would do.
I am far from being an expert, but I have always applied the filler directly to clean metal and haven't had any failures that I know of. But, in attempt to keep up with the times, the body work that I did recently was done with epoxy primer first and filler over it. After the preliminary sanding I've decided that I don't like the process and I'll be doing the rest of the body work the way I've always done it, direct to metal. I did a lot of structural bonding in the aerospace industry and I don't like the way the filler adheres to the epoxy. Just my opinion, but the filler just seems to bond more tightly to the bare metal.
As to the rust underneath, if rust is evident I use Jasco metal etch to stop it. Any holes are welded up so moisture doesn't have access from the backside. And since primer and filler are both porous, I don't do any body work and priming until I'm ready to carry through to the final paint.

 

Three years ago my daughter's car got T-boned. She came in the house one day and said Daddy! Daddy! I got a big rust spot under my door . I went out and looked and in the middle of the rust spot was a seam. Went back to the body shop and the guy said that quarter included part of the rocker they applied body filler over the seam , painted it ,He was nice about it and redid it I gave him some of magic elixir to put over the seam first and then the body filler. And the debate rages on love these discussions.

 

I epoxy everything first, and have done so for 25+ years.

Many paint jobs have faded, and clearcoats have failed, but not one single one has had a filer application come loose, unless it was in an accident.

If a bare metal part is in my shop, it gets sprayed with a few coats of epoxy, with the top coats being thinned to reduce the porosity.

For short-term bare stuff, it gets coated with Ospho.

 

I've seen a few like that. Seams on lower body that rust under the filler. My theory is that the welds have some minute porosity that allows moisture to enter from the back. May not be true, but that is why I use a coat of epoxy, unthinned , and brushed on all seams before spraying an overall coat. May not be the cause, and may not help, but it makes me feel good.

 

Rust in non factory seam in a repair area has a couple factors.
A new car is typically uni-side. Like the brookville 32s
The section location in almost all instances is recommended by the manufacturer to be a butt weld.
This is less prone for corrosion. Plus a rust inhibiting cavity wax is used in the sectioned locations where normal paint products can not be used.
Some newer changes is the use of silicon bronze in these areas.
I will not overlap a non factory joint.
Epoxy and filler?
I’ve done em both ways. No issues with either.
The only filler failure I experienced was a flat hood that cracked due to vibrations and/or engine heat.

 

I just ordered some DTM epoxy primer so I can see which way is best. Thanks

 

Anyone still use the metal prep products with epoxy?

 

^^ Not in recent years. We did this: Metal Prep, DP90 then the filler. Topped w/more DP at a place called Arrow Fire Apparatus in Broken Arrow, OK back in the mid 80's. I then used the same approach on my '77 SWB. Except it was then coated w/high build & blocked. Then sealer. I follow Scot Sullivan on the social networks & he still does this step by step.

 

I have always been in the "primer first" camp & like I just said in another paint thread...With the high quality DTM/DTR made by companies like Tamco these days, I would not take a chance putting the filler on 1st anyway. As far as the video goes, I also agree with Anthony. Too many variables.

God Bless
Bill
https://www.jalopyjournal.com/forum...ar-transport-hauling-open-or-enclosed.614419/

 

I’ve read this in some epoxy tech sheets.
“For best results, use cleaner xxxxx(metal prep)”
Wondering if anyone still does that

 

Yes, PPG DX579 and DX520

 

I'm a self taught hack, so I've pretty much discovered about every method there is to screwing up doing body filler. Through my vast years of experience, I've discovered a few things that have been pretty consistent.
There are generally 4 reasons for body filler failure.
1) The metal has been bent or flexed, and the filler either cracked/broke, or has been pulled off of the metal. Metal bends, plastic filler doesn't. Oil canning metal covered with filler falls into this group too.
2) New filler has been added on top of old filler. Fails nearly every time.
3) The metal under the filler has holes in it that allow moisture to get between the metal and the filler.
4) The filler is way too thick.
That said, I'm old school, I apply filler directly over the bare steel, because that is how I've always done it, and most of the filler failures fall under one of the four reasons above. I also want to point out, I'm still learning. I'm sure I'll find new ways to screw up body work. Gene