Issues with epoxy bond under filler

M

mrennie

Promoted Users
Hello, my first post!

I'm having an issue with epoxy primer losing its bond to the sheet metal in two areas where I have put filler over top.
It has happened twice, first with RM epoxy, then with SPI epoxy, so I don’t think it is the primer.

What has happened is that after applying the filler and letting it cure, when I sand with 80 grit to shape it, if I break through to bare metal, instead of the primer feathering out it sands rough and I can scrape it off with my fingernail. It only seems this way close to and under the filler. In other areas where there is no filler I cannot scrape off the primer.

Sheet metal was cleaned with solvent W&G remover then sanded with 80 grit disc, cleaned with waterborne W&G remover, dried for several hours, epoxy primed, then with RM primer I waited 24 hours, and the SPI I waited 48 hours before applying filler.

The filler is Ever coat Metal 2 Metal that uses liquid hardener if that matters.

Do I need to wait longer before applying this filler, or wait longer to sand it?

Suggestions appreciated.

Thanks

Michael
 
First the metal filler should be applied to bare metal, not epoxy but this is not what is causing the problem.
I will give you the three things that will cause this and you decide.

Acid film on metal.
Second, metal was cold or temp was cold when epoxy was sprayed.
Third. Filler or primer applied to fast to the epoxy.
I can think of no other reason that will cause the epoxy to soften.
 
epoxy is a funny animal. it can feel dry but its not necessarily cured which is what barrys list touches on. epoxy is slow to cross link and become chemically resistant so when you apply filler or poly primer over it the epoxy will soak up the chemicals out of the polyester and it will soften. when the filler or poly primer cures it becomes a solvent barrier trapping the solvents in the epoxy film. epoxy also cures extremely slow when there are solvents in the film so the epoxy will harden eventually but it may take a very long time. during the summer months with 2 med coats of epoxy then 24hrs is needed before you apply filler or polyprimer. wintertime really depends. if you have 3 good coats down and its 50 deg then it could take 1-2 weeks
 
I completely agree, no epoxy under metal to metal, or anything that uses the clear liquid type hardener.

We learned this when we ran out of icing and ran to the parts store to get some red spot putty. That crap softens everything you have worked with, especially if you use it from the shelf of the auto parts store and it starts out runny. That liquid will soften anything down to metal.

This might be different if your epoxy was cured for a good 6 months before starting. I was watching some show, I think it was the grave yard cars goof. I rarely watch that one because I am not a mopar guy, but passing thru, they were using a new dupont primer, it was critical on the mix so the owner dude did it himself, the guy sprayed it down like it was slick sand, and he said its going to sit and harden for 30 days before the body guys get to work on it.

Anyway, that clear hardener should be the key to biting into metal or ruining epoxy.
 
Thanks for the replies, you have given me lots to consider.

To answer the question of why I used Metal 2 Metal over epoxy instead of bare metal, I wanted the epoxy applied first for corrosion protection.

All of Evercoat's fillers including Rage/Rage Gold/Rage Extreme say to apply directly to metal, none recommend applying over epoxy even though most hobbyists are doing that now, so I did not see any reason why Metal 2 Metal would be different as I believed it to simply be an aluminum based instead of talc based filler. The reason I am using Metal 2 Metal instead of regular filler is that the areas in question are patch panel weld seams and I did not want to use a talc based filler just in case I have a pinhole in one of the welds allowing moisture through from the back side.

My garage is heated and priming was done at 72F and stayed that way the entire time since. Regarding acid film, the panels were wiped with an RM phosphoric acid based metal conditioner to neutralize some rust staining that appeared when the garage got humid last summer (I have since installed a dehumidifier) but the metal was thoroughly sanded with 80 grit and wiped with W&G remover before the application of primer, so I don't believe this is a residue issue. This jives with the fact that the soft primer is only under the filler and not the rest of the panel.

So it may be the filler being too hot chemically vs the amount of time I let the epoxy cure.

If the liquid hardener that different than the cream? (I realize they are not interchangeable)
 
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One more question, if the epoxy had softened because of the filler solvents, is it reasonable to think that if left alone and given sufficient time it would cure at some point and still have a good bond? Or does the fact that it softened mean the bond to the metal has been compromised? I am asking because I have one other area I applied the same filler over epoxy and when I sanded the filler I did not break through to bare metal and therefore did not see any issues with feather-edge or softening.
 
the adhesion should be fine after full cure, don't worry about the clear hardener being an issue-I've applied polyester fiberglass resin over spi epoxy many times and never had any issues and I would bet it's the same MEKP hardener
 
"My garage is heated and priming was done at 72F and stayed that way the entire time since. Regarding acid film, the panels were wiped with an RM phosphoric acid based metal conditioner to neutralize some rust staining that appeared when the garage got humid last summer"
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You just answered all the whys in the above statement.
The epoxy over this product never will have full adheision.

How we test for an acid film:
Mix body filler, with a paint stick dab a 1" dia by 1" high, let set 15 minutes or so when hardened up, take a Flathead screw driver slide it under edge of filler and twist, if acid film, the epoxy will soften and pop off, if not you may chip filler at best. This test don't lie.

This is a serious problem.
 
I was going to use metal to metal on my frame to fix some heavy pitting, I had just put 2 coats epoxy on yesterday to get started & saw this so I contacted evercoat to see if M2M was ok for use on epoxy here is the reply-

Hi Justin,

Thank you for contacting ITW Evercoat. If you have the epoxy primer down you just need to be sure it is completely cured. We say 72 hours. If not your next coat of product could possibly bubble up. The epoxy will need to sanded and cleaned before applying the Metal-2-Metal. I have attached a tech sheet for review. Thank you again for your interest in ITW Evercoat products.
 
". . . wiped with an RM phosphoric acid based metal conditioner to neutralize some rust staining . . ."
I can attest to what Barry says about this stuff causing adhesion failure. I used a similar product on the roof on my Coronet R/T and when it came time to buff the clear a little blister would form and then go away as soon as I lifted the buffer up. I noticed this happening in a couple of places and eventually cut in to one of the blisters to see what was going on. I could literally flick the paint off with the edge of my razor blade. It took everything off all the way to the metal and on there was this black film from the rust preventative wipe I used. That was the only place on the whole car I used it and sure enough I had to strip the entire roof and start over again.
 
Listen to Barry. He knows what he is talking about. You don't want to hear this but you need remove to metal anywhere you used the acid metal conditioner. You did not neutralize it properly.
 
Thanks again for the great info.

I will do Barry's adhesion test in several spots to see what happens. The RM products I were using (before the VOC rules changed here and became unavailable) were RM 801 metal conditioner and RM 589/789 epoxy primer. The instructions for their metal conditioner are a bit different than others I have seen, it is mixed 1 part to 2 parts water, and after scrubbing with steel wool for a minute it is wiped off wet, nothing was left on the panel to dry and I did not see any visible film. No neutralizing or rinsing is recommended, in fact, one time when I did wipe a freshly conditioned panel with a wet rag it started to rust again in a few hours so not sure if this means this particular product is more benign than others or not.

In any event, the challenge now is that using this conditioner was recommended to me by the RM rep for use under their epoxy to improve adhesion and the P-sheets for both their EP589/789 epoxy and 801 metal conditioner do not say they are incompatible, only that the metal conditioner cannot be used with their acid wash primer which I am not using. I have many areas on the car where there were rust stains that I have used this conditioner and then applied the RM epoxy over top and have seen no issues, but since I am still at primer and filler stage now is the time to do some checking before I get too far into it to be sure.

When I ran out of the RM product and switched to the SPI epoxy, I was fully aware that it is not compatible with metal conditioners, so any areas I applied it to bare metal were sanded with 80 grit and washed with W&G remover. Is there something else I would have to do in the event that this is the problem?

I do appreciate the feedback, and happy that Justin passed along his info that the filler I am using should wait until 3 days have passed before applying over epoxy (I tried 1 day then 2 days, so appears I was premature). Before I freak out and start stripping off all primer work I have done, I think it makes sense to do that adhesion test in 5 or 6 locations and see what I find.
 
87max said:
I was going to use metal to metal on my frame to fix some heavy pitting, I had just put 2 coats epoxy on yesterday to get started & saw this so I contacted evercoat to see if M2M was ok for use on epoxy here is the reply-

Hi Justin,

Thank you for contacting ITW Evercoat. If you have the epoxy primer down you just need to be sure it is completely cured. We say 72 hours. If not your next coat of product could possibly bubble up. The epoxy will need to sanded and cleaned before applying the Metal-2-Metal. I have attached a tech sheet for review. Thank you again for your interest in ITW Evercoat products.
Click to expand...

I really like metal 2 metal too, well as long as you sand the real heavy parts right after it cures, so its really tough to know what to do. I thought the entire chemical cure of the epoxy was weeks, if not months though. I would consider the 72 hours is good if you are talking about working in optimum conditions.
 
When using a Phosphoric acid based treatment you need to neutralize it properly. Once the rust is converted it should turn black. If left like this it will turn chalky white after a day or so and you can wipe this film off with your finger. The method I use to neutralize it is as follows: Working a section at a time, apply another coat of the Phosphoric acid and while it is still wet wash it off with soap and water using a red scotchbrite. Rinse it well with water and then dry with compressed air.

As always I will defer to the pros who may have a better method but this has worked for me.
 
What these people are trying to accomplish is the same as iron phosphate that is required under every industrial steel paint job. Its the same iron phosphate that new cars are dipped into as the pretreatment specification before priming. Industial side, it actually replaces primer. Its just like the military starting with the wash primer or what we call acid etch primers, that add that phosphoric acid into the primer to get it to bite. The reason it does not work in this industry is people do not understand it needs to go on at about a half a mil dust coat to do its job. Why even bother doing the step if you are going to introduce water and scotch brite the coating you just put on the steel or DA it with 80 grit?

This industry, more is better. We got into that Ospho after reading about it here, and yes, if you leave it dry, and you put too much on, its a white powder all over. If you see that white powder, you have used the product to its capacity and there is no longer any treatment happening to the steel. I just feel there is a line that gets crossed with the SPI products and all these issues end up starting because the other stuff was used wrong. Metal to metal is an aluminum dust powder, that turns to metal, and metal is what you are supposed to prime over.
 
"Why even bother doing the step if you are going to introduce water and scotch brite the coating you just put on the steel or DA it with 80 grit?"

If red scotchbrite and soapy water remove the converted rusty metal you have bigger problems that what the treatment was meant to address.
 
I think I should be OK.

I mixed up a bit of Rage Extreme, and placed the 1" x 1" blobs of filler in 11 locations on my body, all were where I had used the RM metal conditioner under RM primer and had sanded through that primer and had SPI primer over top of the bare metal.

I waited 20 minutes for the filler to harden, and wedged a large flat screwdriver under the edge of the blob and tried to pop them off.

9 of them just had filler break off in small chunks and the blob did not come off.

The other 2 blobs, they were shaped funny (vertical surfaces so the filler sagged) and had a good overhang, so when I shoved the screwdriver under the overhang and gave it a good twist, these 2 blobs came off but the primer underneath did NOT come off with the blob. The primer was smooth and intact but stained from the filler.

On the 2 locations where the filler popped off with no primer, the primer was soft and I could scrape it off with my fingernail, right the up to the edge of where the blob was. As soon as I got to where the blob stopped, the filler was hard and would not scrape off. One of these spots where I scraped it off was bare metal underneath but not black or discoloured, and the other spot where I scraped off the primer the surface below was the previous coat of primer which obviously had no acid treatment applied to it.

All these locations where primed 96 hours ago, and it sure appears to me that my only issue is that the filler softens the epoxy under the filler, so I think my original issue was applying filler too soon.

Make sense?
 
anotheridiot said:
What these people are trying to accomplish is the same as iron phosphate that is required under every industrial steel paint job. Its the same iron phosphate that new cars are dipped into as the pretreatment specification before priming. Industial side, it actually replaces primer. Its just like the military starting with the wash primer or what we call acid etch primers, that add that phosphoric acid into the primer to get it to bite. The reason it does not work in this industry is people do not understand it needs to go on at about a half a mil dust coat to do its job. Why even bother doing the step if you are going to introduce water and scotch brite the coating you just put on the steel or DA it with 80 grit?

This industry, more is better. We got into that Ospho after reading about it here, and yes, if you leave it dry, and you put too much on, its a white powder all over. If you see that white powder, you have used the product to its capacity and there is no longer any treatment happening to the steel. I just feel there is a line that gets crossed with the SPI products and all these issues end up starting because the other stuff was used wrong. Metal to metal is an aluminum dust powder, that turns to metal, and metal is what you are supposed to prime over.
Click to expand...

You are still clinging to Old Tech. Epoxy is New Tech. It's been said a thousand times but here it goes, If you are going to apply an Epoxy primer over something that you used a phosphoric acid treatment on you need to neutralize the acid. Hence the reason for water. Epoxy will not bond with an acid film which is what you have left after using a phosphoric acid based metal treatment. The bond epoxy has with clean bare steel is far superior to anything you can get with an acid based etch primer or using a phosphoric acid based metal treatment. I don't care what industry you are talking about epoxy will not bond properly over an acid film.
 
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