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My body guy says epoxy prime first, then bondo/fiberall/whatever. we do however cut out rust/weld before epoxy primer so we don't have to smell the fumes. I recall he said you could bondo first (but it was better the other way)
 

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The caveat to applying filler directly to metal before primer is moisture trapped between the filler and the metal. The caveat to applying filler over epoxy primer is the filler lifting the primer off the metal. I've read a lot from both camps and people will cite this "study": Epoxy or No Epoxy Under Filler - Autobodystore where the bond between filler and epoxy vs the epoxy and metal can fail with enough force under the right circumstances. I think either way, you could find fault with the process the author uses to rationalize filler over epoxy or use it to prove the point of filler over metal. After all of the reading I've done on the net, I'm still undecided but tend to error on the side of caution in that fillers were designed to be applied directly to metal. PPG has even been cited as saying that you can apply filler to DPLF and then apply more DP over that to seal it but then again, they want to sell more primer.

If your metal is warm and dry when you apply, moisture shouldn't be a problem. mikemstang66 states that filler has h2o in it. Really? I thought it was just talc and polyester resin. It absorbs water when it's cured but I wasn't aware that it contains water.
 

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Lots of bad word of mouth info on this subject. This includeds info from experienced professionals.

A discussion with owner of SPI paint pulled together some other facts.

The strongest bond is epoxy paint to properly prepared metal. This means the proper sand scratch or sandblasting. Then properly prepped and painted.

During the recoat window the epoxy paint has an open face and the filler strands will go into these holes. The heat of curing filler will help cure the epoxy which closes the holes on the filler strands.

From a restorers point of view you really want to get epoxy on the metal first. You get a total block of moisture so you will not get much rust formation under the epoxy. Every little pit you leave behind with a microscopic piece of rust will use all available oxygen and continue to rust a small amount. No, those rust cures do not really get all the rust in the pit. Longer story for later.

Yes you can put filler directly to metal. You MUST use the proper grit paper. The 40 grit some pros recommend is wrong. Some deep scratches, but too much space between the scratch. You must follow what the directions say. More scratch per inch is better!!!.

The shops put the filler on first because it is a faster way to get the project done. Time is money for them. The hobbyist is typically slower and needs to get the metal protected first. So for a hobbyist it may be better to epoxy.

What is best for you is dependent on your situation. You can only make that choice after taking time to read about and understand the products and what they can do for you.
 

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whatever method you want.

my guess is since you are asking the question that you may not have the experience to prime and then do your filler in one shot without cutting thru the epoxy in the process. thus i would probably guess filler first for you.

filler will grab to the metal very well if you have it scuffed well. try removing the stuff after it's really cured. it's not easy (i'm not talking about the the cases where it's caked in).
 

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whatever method you want.

my guess is since you are asking the question that you may not have the experience to prime and then do your filler in one shot without cutting thru the epoxy in the process. thus i would probably guess filler first for you.

filler will grab to the metal very well if you have it scuffed well. try removing the stuff after it's really cured. it's not easy (i'm not talking about the the cases where it's caked in).
I guess this is what I was hoping to hear as it would suit me to spray the epoxy on now and apply the filler later, probably next weekend.

Thanks everyone for your input.
 

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Agh.. Since the chem engineers usually, if not ALWAYS (Although sometimes they say no necessary) filler first, THEN primer.. as I said before on this board, I'll go with the chem engineer over a body man any day of the week.

Mike, before spreading possible misinformation, please cite an MSDS or TDS where it says H20 is present in body filler.
 

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FWIW, I just finished stripping the body shell of my 65 fastback. The 35 year old filler was still tenaciously attached to the metal and ther was NO sign of rust under it. This was with older technology product and lacquer primer. I plan to follow the same order with the newer products and, added to the fact that this car will rarely if ever see rain, I don't expect any issues. Filler, primer, paint. It works just as designed.
 

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There is practicality for the hobbyist.
If you are full time shop, it isn't difficult to strip a spot, apply filler, feather it out, then spray epoxy primer on it.

For me, I can not spray epoxy primer, which I think most of the good stuff has isocyanates in it, in an attached garage.

Nor do I think it is a good idea to leave a car in bare steel for months or years on end while the metal work is done awaiting filler and primer.

Anyway,
For the above reasons, I plan to have mine ecoated after the metalwork is done.

Wherever I need filler will most likely go over the ecoat, unless I find a convincing thread that filler doesn't stick to ecoat...
 

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Yeah, that's pretty damn intense for the hobbyist.

There should be no problem leaving it as bare steel if it's protected from the elements. Mine has been that way for months now. And rust shows up in the form of a handprint, but that's my fault. Nothing that doesn't come off with half a second of sandpaper.
 

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i only use PPG DPLF. It doesn't have iso's. if it does, then i'm unable to read.
Good to know, I have read the MSDS on some of the DPLFs and they sound pretty scary to spray in an attached garage with bedrooms overhead. BTW, part of my fear of Isos came from your posts in this thread:
http://forums.vintage-mustang.com/vintage-mustang-forum/620860-paint-prep-new-floorpans-2.html

When you say DPLF, which ones do you use? I thought there are several different ones, DP40, DP74, DP90?


never heard of a hobbyist doing this.
Yeah, I surprised it isn't more popular. It isn't all that expensive and it gets protection in most (all?) the nooks and crannies.

I posted a some pictures in another thread of a car being done, but caught some grief because they were of a Mopar, lol.
 

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Yeah, that's pretty damn intense for the hobbyist.
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There should be no problem leaving it as bare steel if it's protected from the elements. Mine has been that way for months now. And rust shows up in the form of a handprint, but that's my fault. Nothing that doesn't come off with half a second of sandpaper.
You must work a lot faster than me, my metal work has been going on for years. Or maybe you are in an area with much less humidity.

I kept the surface rust away with a chemical solution, but I fairly recently learned that adversely affects epoxy primer adhesion. Ask how much it affects adhesion on the hotrodders board and a flame war is sure to break out, lol. That's another reason I'm going for the ecoat ,as they say that phosphated surface won't affect the ecoat adhesion (I think one of their initial steps may even be a phosphate dip, but I'm not sure of that)..
 

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Never said I was DONE the metal work. :D Well it's winter now, so humidity is down. She was getting pretty bad in the humid humid summer, but as I said, nothing a little hit with sandpaper didn't take care of. I assume I'll have to give it a once over in spring before I hit it with epoxy.
 

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Good to know, I have read the MSDS on some of the DPLFs and they sound pretty scary to spray in an attached garage with bedrooms overhead. BTW, part of my fear of Isos came from your posts in this thread:
http://forums.vintage-mustang.com/vintage-mustang-forum/620860-paint-prep-new-floorpans-2.html

When you say DPLF, which ones do you use? I thought there are several different ones, DP40, DP74, DP90?

Yeah, I surprised it isn't more popular. It isn't all that expensive and it gets protection in most (all?) the nooks and crannies.

I posted a some pictures in another thread of a car being done, but caught some grief because they were of a Mopar, lol.
there is a lot of BS on these forums and people repeating garbage info.

i was merely saying no iso's in the DPLF. I didn't say that paint in general isn't nasty. wear your mask, and get some air flow in your house. it really doesn't matter what you spray, you need to do that. (aka, common sense).

DP40, DP74, DP90 are just different colors. i use DP401LF catalyst instead of DP402LF.

you're living in a fantasy world, if you believe you will successfully e-coat a car, then do your filler work and not ever cut through the e-coat.


if you are going to take a long period of time before sealing the panel then it only makes sense to seal the panel first. when i media blasted my car i immediately epoxied it because i knew it was going to be awhile before i had all the final metal work done. when i stripped off the e-coat from the skin of the door, i did the filler work, then the epoxy because it was complete in a week.
 

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Wow, that question opened a can of worms didn't it? I'm no body-man, but it looks to me like if the pro's can't determine which method is good or bad, the layman can pick whatever it easiest and run with it.

After all any drawbacks to a given method are pretty hard to define and will show up years later, if at all.
 

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you're living in a fantasy world, if you believe you will successfully e-coat a car, then do your filler work and not ever cut through the e-coat.
When did I say that? There are many reasons I plan on using the ecoat. Mainly to get into the frame rails, A pillar, B Pillar, under the roof support, cowl and other places sandpaper will not go. It will also keep the entire car from "flashing". If I sand through it somewhere, so what?
 
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