Epoxy primer.... To bondo before or after

[xero_xero]

I have a 75, with a good amount of rust being cut out, weld, grind, lather, rinse, repeat as necessary.

i want to seal the body up, as its sitting in my driveway and surface rust is a big issue. i have a few coats of primer on the surfaces that i have stripped completely, but i am looking to Epoxy prime the entire bodyline. the underside will receive por15 with undercoating.

now, do you prefer or have experience bondoing before or after the epoxy coat. The only thing that worries me about spreading putty after is the possibility of breaking through the epoxy coat, and loosing that protection.

 

My process as follows,
Flapdisc strip - reason being i have three coats of paint and body work to cut through

aerosol prime to protect from elements

Sheetmetal bodywork with no bondo

Airfile smooth - and epoxycoat within 24 hours

Bondo filler to the absolute minimum

huigh build primer.
 

 

thoughts?

[Jay Gadsby]

That is how I have done it. Epoxy binds best to a metal substrate, and bondo will adhere to epoxy, just needs to be scuffed. I am no pro, but did lots of reading before I did my 240sx in my garage (still cleaning red over spray).

[socorob]

Make sure you use a bondo that's made to go over primer. I think one is rage gold extreme by evercoat. Ask the people at the body shop supply when you go to get it.

[OldAndyAndTheSea]

Bondo before.

 

If you apply filler over the primer, as mentioned, look for a polyester glazing putty, as they are designed to do so. The typical bondo doesn't like to bond to paint/primers.

 

And you'll be breaking through the epoxy primer when you block, that's actually what you look for initially. So that, and multiple recoat/block sessions are to be expected.

Edited October 18, 2014 by OldAndyAndTheSea

[Jay Gadsby]

X2 on the Ever coat product line. I used their poly glaze and it works nice, sands nice and had no issue with bondo bleed through.

[xero_xero]

That is how I have done it. Epoxy binds best to a metal substrate, and bondo will adhere to epoxy, just needs to be scuffed. I am no pro, but did lots of reading before I did my 240sx in my garage (still cleaning red over spray).

 

Overspray isnt a problem, ill be spraying most of the primer in the driveway, then carry it to a booth to handle the base/clear....  been there, done that too many times.

 

from what i have read, epoxy binds best to metal substrate, but they list nothing else.

 

Make sure you use a bondo that's made to go over primer. I think one is rage gold extreme by evercoat. Ask the people at the body shop supply when you go to get it.

 

i have heard of evercoat, and i have a gallon of bondo sitting in my garage now thats actually bondo brand.

 

Bondo before.

 

If you apply filler over the primer, as mentioned, look for a polyester glazing putty, as they are designed to do so. The typical bondo doesn't like to bond to paint/primers.

 

And you'll be breaking through the epoxy primer when you block, that's actually what you look for initially. So that, and multiple recoat/block sessions are to be expected.

 

i thought the same thing, then, i read about how body fillers of different brands actually have issues with creating a rust inhibiting situation. but that w2as geared towards specific brands if i remember correctly.

 

X2 on the Ever coat product line. I used their poly glaze and it works nice, sands nice and had no issue with bondo bleed through.

 

Specific product lines always help, as well as reinforcing the products that have been used and proven. thanks!

[socorob]

Just make sure ti get their one designed to go over primer if you decide to go that route. I think rage gold is made for bare metal and rage gold extreme is made to go over primer. Apparently helps protect against filler absorbing water causing rust. Last time I bought it I got the wrong one, as the cans looked similar then.

[Jay Gadsby]

For the base fill I used the normal autozone bondo bucket. Didn't care for it, but it got the job done. All was applied over the epoxy base primer. Scuffed with 180 prior to application. The stuff I used for the final touches was ever coat easy sand found here:

http://www.evercoat.com/productDetail.aspx?pID=4

 

They have a very extensive line, and any jobber can usually point you to the exact product you will need. I read more about painting than i ever thought i would before doing any part. Auto body101.Com had a lot of good info about fillers and primers.

[Chris_Hamilton]

My 2 cents, Any quality body filler will bond with epoxy primer as long as the primer is within the re-coat window. With most epoxy primers this is 48-72 hours from when you sprayed it. I personally never go past 48 hours, if I do I scuff the primer with a red 3m scotch brite pad and reapply 1 coat, Then apply body filler. Whenever you are in doubt how to use a product, go to their website and find the "Technical Data Sheet" for the product. It should answer your questions 99% of the time. There is so much misinformation in this thread it's funny.

[RPMS]

Bondo first, or you will break through the primer when you sand it down.

[Chris_Hamilton]

Bondo first, or you will break through the primer when you sand it down.

 

If you break through you simply recoat those areas with epoxy prior to reapplying body filler. If you apply epoxy prior to any filler work, then reapply after you sand your filler (before reapplying any more filler if you have bare steel areas) you'll have 100% coverage. The main source of problems people encounter when using filler over epoxy is applying filler outside of the re-coat windo of the epoxy. That's when you have adhesion issues.  Epoxy provides a chemical bond to body filler not a mechanical bond like applying filler over scratched metal. That is the main reason for applying filler over epoxy rather than bare metal, not corrosion protection. Corrosion protection is a secondary benefit as filler is pourous and can absorb moisture. the e-prime provides a barrier between the metal and the body filler.

It is also a good idea when block sanding primer (urethane, poly etc) to spot coat any bare steel areas you may create during the sanding process prior to reapplying more urethane primer (or poly primer etc.)

[RPMS]

Your point about repainting after sanding is a good one, with the caveat that the primer will build up in the he areas where it didn't get sanded off. It took me a half dozen tries before I was satisfied with my body filler. That's a lot of coats of paint, but if he's better at managing overspray than I am, it might not be a big deal.

 

I ask this out of ignorance, since I've seen both paint and filler pop off. Is there hard evidence that primer adheres better than properly applied filler? Whichever adheres better should obviously go against the metal.

[OldAndyAndTheSea]

It all depends on the composition of the materials you intend on using. I think that's the message you should take away from this thread.

Body filler is like cake batter. There are lots of different flavors to choose from. Primers too...

Why don't you tell us what materials you plan on using and we could go from there?

There are nine ways to skin a cat. Filler before, filler after..if you used the (proper) materials properly, you will not have problems.

As mentioned, if you are in doubt, look at the product data sheet.

And guys....you're supposed to break through the primer when you block, at least initially. That's all part of the blocking process. Those break throughs are transitioning the worked areas into the good areas of the panel. If you get the car straight without breaking through in the initial blocking stages, you are a freaking wizard....or your car isn't as straight as you think it is.

 

 

<--- ASE Body Mechanic coming up on 10 years. Also certified in Open molding, Vacuum infusion, and LRTM composites processes. . This is RIGHT up my alley.

 

 

Also, some good reading. All of the information you are looking for is in the link I provided.

 

Understanding the composition of both polyester and epoxy makes a big difference, as these two materials don't always mate the same way. (Polyester body fillers DO NOT chemically bond with epoxy primers, as they are opposing compositions. Polyester does not like to stick to epoxy, however epoxy WILL stick to polyester.)

 

http://www.roadsters.com/filler/

 

EDIT: and don't forget the guide coat! That'll take the guess work out of straightness.

Edited October 28, 2014 by OldAndyAndTheSea

[FricFrac]

Body filler bites best with a mechanical bond.  Rough up the metal with 40 grit and that seems to give you optimal adhesion.  Personally I'd go with body filler to metal with the epoxy primer as the last product before paint.  That was the advice from my paint supplier and it seems to work.

[Chris_Hamilton]

@OldAndy

That article has been reposted all over the internet, technically perhaps filler to epoxy is not a chemical bond but for the sake of this discussion it's easier to call it that.

Ok I'll go over my experience with it and try to sum up why epoxy before filler is best especially in a restoration environment.

 

I'm 44 years old. been doing this full time since I was 20 (had to drop out of college after my Dad died). That's not counting the time I spent growing up in my Dad's  Collision Repair Shop. I have been I-Car certified since the mid '90's,I have passed the I-Car welding test,  PPG Master Level Refinish Certification, and I have had been through the Mercedes Benz Collision Repair training as well. Certified by MB-USA to do Collision Repair on Mercedes. (I-Car is the Collision Industry Standard much like ASE is to mechanics)

Currently I do mainly Restoration type work and often do repairs of botched "Restorations" by so called "Pro's".

The First time I ever heard of putting epoxy primer on prior to body filler was when I first started my Mercedes Benz training in 1996. They had begun requiring all body filler be applied over epoxy. That's also where I heard the bond referred to as a chemical bond rather than a mechanical bond.

The main reason they required it (and now so do many many other manufacturers, Porsche, Audi, VW, among others) is for the corrosion resistance and the adhesion. By adhesion I mean the "grip" but also the fact that when you apply body filler it cures by catalyzation. A by-product of this is heat which can cause the bare metal underneath the filler to "sweat" which in turn can and will cause the metal to rust (esp if the filler is open and not primed for any extended length of time). OldAndy posted a article about heating the metal up or only applying it in environment above a certain temp.  That's all well and good but if you warm your room up to 75 and the filler warms up to 140(it can and does reach this temp)  that is still a big enough difference to cause condensation. By laying down a barrier(epoxy) you no longer have to worry about moisture on metal)

One more thing if you're not convinced, say you are restoring a car in your spare time, mainly on the weekends. Perhaps you started doin filler work a month or 2 ago. Maybe it's rained a couple of times since you started. No big deal you have a nice dry garage. But you have been working filler and have a lot of exposed unprimed filler, because you are not ready to prime the car yet. Grind a small amount away and look carefully at it while you are removing the filler. More than likely you will see rust speckles on the metal. Hmmmmmmm.

 

Here is a good discussion over at the Southern Polyurethane forum. http://www.spiuserforum.com/showthread.php?1289-Filler-to-bare-metal-causing-metal-to-sweat-!-What

Read through and then decide whether or not you want to continue to use body filler over metal. Sometimes just because someone has done it a certain way all their life doesn't mean there isn't a better way.

[Nelsonian]

^^^ Very well put. It makes me feel more relieved that I went this route with my rebuild. Car was blasted, Endura epoxy primed, then filler added as is needed. The epoxy primer has been on the car for two years now in a San Diego garage where it is having body work done, and is holding up great.

[OldAndyAndTheSea]

Good points....

 

However.

 

My post was not intended to come off as a dick measuring contest. I'm a science guy. I like the facts.

 

I was mainly just affirming the fact that there really is no set "best" way to do this. An ideal that HybridZ will often recognize..  It is all so very dependent on a myriad of variables.

 

I mainly responded to your claim that a chemical bond occurs between polyester fillers and epoxy primers. Which simply does not. Anecdotal evidence, or not... That's the science. I honestly wouldn't have responded had you not made (the ironic in my mind) statement about misinformation in this thread. Then go and state your own....

 

In the thread you provided, which was a good discussion by the way, someone also made this claim.

Edited November 1, 2014 by OldAndyAndTheSea

[Chris_Hamilton]

@OldAndy  If you want to get pedantic about it YES I was in error I should have called it a "adhesive bond", but that doesn't take away or make in error what I was saying. And no I wasn't trying to get into a dick measuring contest just stating my experience in reference to what I was talking about. .  I believe you did that as well, being an "ASE Certified Body Mechanic"...... never heard a body guy refer to himself as a Body Mechanic before.

 

Anyways people can do what they want to do, just thought I'd share some of my insight on a subject I have experience with at a Professional Level. Peace.

[OldAndyAndTheSea]

Chris

 

Never did I say you were wrong. In fact, I agree with practically everything you said... Other than the aforementioned comment.

 

There are many arguments/counterpoints to each side of the discussion, that's all.

 

I just didn't want this thread to get dragged through the mud as many have in the past. Too late for that now, I guess....

 

But when discussing bonding. Getting the type of bond correct is kind of a big deal.

 

 

All it takes is one shred of inaccuracy to completely shatter someone's legitimacy. Unfortunately, this is the internet.

 

 

And body mechanic is a pretty common term in this region. Surely this isn't the first time you've heard it.

 

 

Again, no disrespect here. I like a good open debate. In fact, I promote them.

Edited November 1, 2014 by OldAndyAndTheSea