Hi, me and a friend of mine are replacing a big section of my firewall. we already welded in the patch and are getting ready to start using fiberal, and then bodyfiller. he says that we should first use self ethichg primer and spray everythign, and then start doing the bodywork. Thought i would run it past you guys first! thanks

All you have to do is read the tech sheets for the products you are using. If you do, you will see that no manufacture (that I know of) recommends applying filler over etch. In fact, there is only one that I know of that even recommends applying etch over filler. Most every manufacture says DO NOT APPLY OVER PLASTIC FILLER. So as a rule etch and plastic filler do not mix.

You could apply epoxy, that is a recommended procedure with most epoxies. But again, read the tech sheets.

Martinsr, i really value your opinion and you have proved to be a very knowledgabel person. So i am not trying to doubt you, just want to run this by you. i talked to my friend and of course he said he has done this a million times,(which probalby doenst' mean much). but he is willing to do it however i want. I am wondering what will protect the metal underneath the body filler? The body filler itself? Or should we just s-can the self etch and use the epoxy like you said? Please review our new revised operation;
1. finish all metal work including grinding
2. use fiberal on pinholes and filling dents and divets
3. after sanding fiberal use Evercoats rage bodyfiller in many various places to get all the firewall panels straight, and sand it all down until acceptable
4. tape off all the body filler and Self Etch prime all bare metal.
5. Use PPG OMNI primer(i think this is what he called it) and prime firewall, sand until acceptable
6. Use a sealer on the primer unless we don't sand through the primer????
7. then get ready for paint.
Does this sound about right? This is my first time doing anythign like this so feel free to correct anything i am saying. I am right around the corner from you; i am over in Berkeley! Thanks again. also I will be doing this whole proceess on the inner fenders also.

The etch i use, R-M Diamont DE-17 tech sheets says Do not apply poleyester fillers over DE-17. It recommends to spray two light coats over bare metal , followed by a 2k primer. Now ive spotted the etch in areas around old paint/filler work, but as a rule as Martin mentioned is they don't mix. Its the Hardener in the filler that reacts with the activator in the etch. IMO the correct procedure is Etch,2k then the filler.
All paint manufactures have slightly different recommended procedures so its always a good idea to read the tech sheet for the product your using. BTW sharp firebird!

Cody, let me get this straight, are you talking etch primer over the filler? Or are you talking polyester filler over the etch primer?

I have been applying plastic filler over the bare metal as 99% of the country does for 25 years. This has not been on a whim, or my brilliant idea, it is the manufactures recommendations. In my travels as a paint rep I never saw one single person apply filler over anything other then bare metal or the occasional previous paint job on minor dings. I do know of a guy here on the net that applys the plastic filler over well cured etch primer, he has never had a failure. YET, this goes against ALL manufactures recommendations. His "success" could be contributed to a number of different things.

Let's start from the begining again. Let's talk recommended procedure. Etch primer over the polyester "plastic" filler (bondo). I have looked through many different manufactures tech sheets (I have a number right here) and only one has a recommendation to apply one of their etches over plastic filler, Sherwin Williams. Now, before I knew this smile.gif I applied DuPonts Variprime over it many times. One note in the S-W tech sheet is interesting. It states that it can be applied over "cured" plastic filler. "Cured" being at least 12 hours. Being all etch primers are basically the same "technology", I have to assume DuPont "could" say the same thing. They are not simply to cover their butt. If people push it and apply the etch too soon over uncured polyester filler, there could be a reaction between something in the two products. My understanding is simply the polyetster resins don't like the acid in the etch. Once the polyester cures, it is no longer "soluable" or at least not as much and it can handle the etch over it.

If you were to apply the etch, then let it cure a day, it would have flashed all it's acid (the acid is in the solvent that flashes) and it would be "safe" for applying polyester filler.

I only present this argument to support that your buddy could very well be doing it with "success".

The FACT still remains that it is not a recommended procedure. I repeat my montra:

Following the manufactures RECOMMENDED procedures will just by the ODDS provide you with better results.

If you want to apply some epoxy then filler, have at it. As long as you use the products that recommend it. Not all epoxies do, I don't imagine. After reading much about it here in the forums I do think this is a good way to go.

FIrst off i was talking about filler OVER the etch primer, this guy loves etch primer and he wanted to use it in part of our process.
So in simple terms;
1. I first do all body filler work over bare metal, and then let cure, and then just use the Omni primer over everything.
2. Or Let the bodyfiller for sure totally cure and then use self etch and then Omni primer,
3. Or Use an Epoxy primer first instead of etch and then do the body filler work and then use the OMNI primer?
Sounds like the first one sounds the best, just do the bodywork and then prime. Is it okay to just use the OMNI primer without any base coat for it to "stick" to? or do I need to After using filler spray something before the OMNI primer?
sorry if i made this sound way too complicated! I just want this done right and i guess am just looking for a firm recomendation, but i guess in this field everyone does stuff differently and you do what works for you.

I agree with Martin, you need to get the tech sheets for EACH product you intend to use and follow them. That will give you the highest rate of success.
Now granted yes you can fly off the tech sheet but the difference between a huge disaster and a good job is KNOWING the product and KNOWING excatly what you are doing when you go off the track from the tech sheet.

I do it almost every day. A good example is when jamming parts. I use PPG clear DC3000, has a dry to buff time of 1.5hrs AIR DRIED, now when I jam parts I add a touch of supercharger which speeds up that cure time. Ive gotten the time cut down to 45mins sand and buff AIR DRIED :eek: . Now I dont sand and buff the inside of parts I do it cus I can hang or handle the parts faster. Got this trick from the PPG rep himself.

Now the downside to this is,#1 Ive got a clear that isnt as abrasive resistance and #2 doesnt have the clearity. I WOULD NEVER EVER THINK OF DOING THIS ON THE OUTSIDE OF A CAR because of the reasons listed. but for jams its a great thing because of the increased production, but yet that method is NOT listed on the tech sheet.

Both the PPG rep and myself have tested this method a few times before we tried it out on customer's cars. I know what I can do and what I can get away with, also know what I CAN NOT do.

As for the etch, PPG says dx1791 can be applied over body filler and slight overlap onto painted surfaces but should be kept minimum. I use Dx1791 and do that method and yet to have problems, also did it on a day basis with dupont variprime and never had problems.

But body filler SHOULD NEVER EVER BE APPLIED OVER ETCH PRIMER .Ive done it...it dont work.

Yes filler can be applied over epoxy primer, but make sure that epoxy is FULLY cured.

Now just my thoughts of epoxy and bare metal. Etch has been proved time after time to be the best corrosion fighter. PPG's epoxy and Dupont's epoxy both stat for max performance etch primer should be applied prior to epoxy.
Both list etch as the first product to be used on bare metal for the lifetime warrenty.

Etch primer as the name implies etches the metal for proper adhesion for future topcoats and also leaves behind a zinc phosphate coating. Epoxy just forms a seal on the metal, unlike etch it doesnt coat the metal with a protective coating.

What like to do when Ive done the filler over epoxy method is first apply etch primer then apply epoxy primer. NOW YOU NEED TO KNOW IF YOUR ETCH AND EPOXY CAN BE USED TOGETHER. Valspar's epoxy is NOT compatiable with etch primer. Valspar makes a good epoxy much better then PPG's DPLF epoxy, use VP50.

I just dont care for epoxy on bare metal especially DPLF epoxy. Not saying its a crap product I just dont like it on bare metal.

Parts of my last 70 chevelle were done with etch,epoxy then filler. Where others were done with filler over bare metal then etch then primer surfacer. My new project car will get done ALL with etch, epoxy then filler. Also doing a mid 30 farmall tractor which will get filler over epoxy.

For someone who doesnt have the skill to knock out a fender in a night or two when doing filler work should probably do filler over epoxy. Or even from the time they strip the part to the time filler work starts, could be days or weeks. Some guys it might take them a week or so to block out that filler, to me thats too long for bare metal to be exposed.

If you do use filler over epoxy be it you apply etch first or use just epoxy, DO YOURSELF A HUGE FAVOR AND BUY QUALITY BODY FILLER, heres a big difference and its just NOT the price.

Id use Evercoat's Rage, rage gold or rage extreme.
Also like Upol products, they make a sweet poly putty that I believe is second to none

I would have to agree, the modern fillers are designed to be used on bare metal, although you will see feathering over primers etc which don't seem to fail in the 15 years I have been around.
Usually, the self etching primers have not created problems over the filler either, So the advice given above regarding reading the specific product instructions is pretty fail safe.
You will get "overlap" before you complete any project I would bet.
Try going to a body shop that has been using the same suppliers for some time, find out who they use,this is the laymans' way of assuring compatibility.