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Discussion Starter #1
All my bolt on sheet metal I've sanded the epoxy primer to a pretty smooth finish before High build primer and paint. I have the body in epoxy now and am sanding it. Is it necessary to sand to this extent or is scuffing good enough? I know it leaves an orange peel look, but high build primer over it will get sanded to a smooth finish. Also, there are a couple areas of epoxy that I sanded down too far to bare metal. Should this be epoxy sprayed again or is the high build primer good enough.
 

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Since you have some sand throughs, I would sand everything with 220 grit or something similar with a DA, then shoot a good solid coat of epoxy over it. Then immediately spray with primer surfacer so that I could quit sanding epoxy and move on.
 

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What Rick said.

But, check the P sheet on the epoxy primer you are using. The epoxy primer I use says wait an hour before putting other primer on.
 

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Immediate was a bad choice of words. Apply it within the time window, usually after the flash time and before a week.

Don't wait 6 months. Point is, spray the primer surfacer the same day or as soon as you can. Otherwise you start back at the same place you are now.

When you sand the primer surfacer, hopefully the surface is level enough that you don't sand through the epoxy.
 

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I had a bad experience shooting high build on epoxy too soon... I would spot prime only the bare metal spots with a very light coatof epoxy, let it dry at least 4 hours then apply the high build . :)
 

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Discussion Starter #6
Thanks for your replys guys. The main reason I did epoxy and sand was time. I didn't have time and space to do all pieces at one time. So, I did them separately. Then prep for high build then eventually paint. Everything went well with the system I used so far. I hate to risk shooting high build too soon after epoxy with different results than I've had. All I have left is the body to finish. But, I hate sanding too.
 

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Block sanding is an art. And, I kind of enjoy that part.
But, I know the feeling when you are done.
It's "Boy, I'm glad I'm finished with that mess."

And, btw, I dry sand thru 400 grit and then go wet for finer stuff.

And a big reminder. When you dry sand, wear a good dust mask!
 

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Discussion Starter #9
Actually, my question never really got answered. There were a couple areas (corner edges) that I sanded through the high build filler primer and epoxy underneath to bare metal. So, can I just shoot a little high build filler primer over these and scuff for paint? Or, do I need to shoot epoxy again, then high build filler primer?
As for the other portion of my question. The body is in epoxy and I was not planning on sanding fairly smooth (I did have a couple areas I knew I would have to use a little body filler to). I did do all my other sheet metal smooth though. I assume even if there are little orange peel divits that don't get scuffed well, the high build filler primer will stick and fill them for sanding? Correct?
 

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I thought I answered your question but you may have needed to read between the lines.

The "right" way is to spray epoxy on the bald spots, and then your 2k primer surfacer.

The "get by" way is to spray primer surfacer on the bald spots and hope you don't sand through again.

I don't understand your question about the orange peel and not sanding on areas that need filler. You MUST apply filler over epoxy with the time window (usually one week) if you're going to do this. Otherwise you need to sand and re-shoot the epoxy and then apply filler. Or just sand it all off and apply filler. Which is what I'd do.

If you have epoxy that's orange peeled and want to shoot primer surfacer after the window time, you need to sand all the peel off, you need to have a fully sanded surface. If you are within the time window, then just shoot the primer surfacer without sanding at all.

The best way to do this is to shoot your primer surfacer right after the epoxy has flashed sufficiently (30-60 minutes for PPG DPLF). Then you'll never have to sand the epoxy, which is the way they meant it to be used. I understand that many of us don't do that because of time constraints.
 

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Discussion Starter #11
Wow. I thought as long as you had epoxy primed (time didn't matter), you just need to sand and scuff good to add filler (bondo) over the top. Does this mean if the window time has elapsed, there will be a failure of the filler to stick?
In the past, I've always tried to do the filler work on bare metal. Then on this site it was mentioned, the preferred way was to epoxy prime then do the filler work. No mention of epoxy primer window time for filler.
 

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Wow. I thought as long as you had epoxy primed (time didn't matter), you just need to sand and scuff good to add filler (bondo) over the top. Does this mean if the window time has elapsed, there will be a failure of the filler to stick?
In the past, I've always tried to do the filler work on bare metal. Then on this site it was mentioned, the preferred way was to epoxy prime then do the filler work. No mention of epoxy primer window time for filler.
What grit did you use to sand the cured epoxy with before applying the filler?
 

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http://www.roadsters.com/filler/ Heres a guy doing it for 30 years, and was a Rage technical rep. Look at what he says in bold letters.
Reed Overson:

"Body fillers do not chemically bond with epoxies. If you put filler over epoxy primer, it has to be fully cured, with no solvents such as thinner or reducer left in the primer, and still should be sanded with a coarse grit and cleaned. In other words, using epoxy primer under filler is a wasted step that may or may not cause adhesion problems later on."

That's pretty much old-school and not the way many pros think today. This goes against what manufacturers of epoxy say too.

The epoxy I use says to use it on bare metal then use polyester filler. No sanding necessary.

From my epoxy's tech sheet:

"Body Fillers:
On any restoration it’s always best to apply the body filler over the epoxy rather than
applying filler over bare metal for best adhesion and corrosion protection. If one coat of
epoxy is used then the body filler can be applied in 60 minutes. When applying two coats
of epoxy, wait over night before applying the body filler. The epoxy does not need to be
sanded before applying the body filler (up to 7 days).
If you choose to do the filler work over bare metal the epoxy can be sprayed over the
sanded body filler."
 

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http://autobodystore.com/filler_&_epoxy.shtml This guys not OLD SCHOOL, the other guy worked for Evercoat! To each his own i guess maybe some epoxies are better then others i guess don't use evercoat rage :D I no compared to filler of 20 years ago no body shop would keep me long i am bad when it comes to cleaning plastic spreaders, that Rage sticks so good on a smooth spreader i don't want to tell you how many i used, i just did the sides of a roof on a 57 where some careless idiot dented it up, the old type fillers you could just twist the spreader and it came all off.
 

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The way I regard the filler over epoxy adhesion tests is that if you use filler over epoxy, you won't get SUPERIOR adhesion, but you will have ADEQUATE adhesion, at least when you use compatible materials correctly and according to the standards set by PPG or whoever. One advantage you have with the epoxy under the filler is the moisture/corrosion barrier from the epoxy.

But if you suspect compatibility, or want the best adhesion, you should apply the filler direct to metal.

Same for the acid containing metal treatments. Find out the combatibility or be sure they are neutralized.
 

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imo what those test proved is the adhesion failure of dplf . i stopped using it when they changed the formula years ago.
i use spi epoxy and also use it for surfacing. it sands really good and i have yet to have any issues with it. will polyester adhere to metal ? of course it will. always has . is it better to put down epoxy first ? imo yes.
i have a media blasting business also and each car gets washed with dawn soap and water then blow dried. i then put 2 coats of epoxy on it . in doing this i have sealed the virgin steel with one of the best adhesion and corrosion resistant product available at this time. no need to worry about rain during transport or any rusty hand prints or any other contaminates. it is totally protected.

one important thing. i will not touch a car that has had ANY kind of acidic prep or product on it. polyester or epoxy will not cure next to it. sooner or later it will create co2 which will result in an adhesion lose and a bubble. every time i get a call about a paint problem there are one of two things that have been used. either metal prep or lacquer thinner.

this is just my opinion based on 42 years in this field . i refuse to argue about it any longer as it is just a waste of time.

this opinion is worth just what you paid for it....... :D
 

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If you know the parts and pieces will be sitting for some time after coming from the media blaster, do you just spray the epoxy primer for right now (I am using HOK KP2CF) and figure on sanding it down later and re-shooting it? Or would you shoot the primer sufacer after the epoxy flashes and leave it sit that way until you get to it?
 

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epoxy or poly primer will have to be sanded after the time window. i epoxy to protect the metal. if past the 7 day window i scuff it good with 180 and red scotchbrite and reapply the epoxy. the spi epoxy has a nice gloss to it so finding minor damage is easy.
 

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"Or would you shoot the primer sufacer after the epoxy flashes and leave it sit that way until you get to it?"

That is the way to use the PPG DPLF, it is what they say to do on their p-sheets. It avoids having to sand and re-apply the epoxy. You will have to sand the primer surfacer as the next step, even though it is later. The sanding also goes much easier, as the primer surfacer sands quite easily where the epoxy does not.
 
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