Technical filler over epoxy, how soon?

OK I got my firewall, dash and radiator shell epoxy primed with nason 491-16 yesterday afternoon.

Now I'm ready to do the bondo part of it but there is nothing in the tech sheets about putting filler on top of it.

How long should you wait to put filler on top? Should it be scuffed first ? If so I take it scuff with 80 grit? Should I wait x amount of time to let epoxy fully cure then filler ?

Can't find much info on the nason 491-16. Thanks gents!

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If it isn't specified you should wait a minimum of 24hrs. Yes you need to sand it to whatever the filler recommends.

 

Yes as K13 said, dry enough that you can dry sand it.

 

Not sure about nason but spi recommends 24 to 48 hours, best to read the data sheets.

 

I’d wait a couple days maybe three if it’s cold outside, scuff where you are applying
Filler.

 

Thanks guys appreciate the feedback!!

@Poverty cap it's been 95+ degree days here so the colds not a problem! Lol

@bill gruendeman yeah I've been thru the sheets and no info on anything but top coating with high build primer.

@K13 @Lloyd's paint & glass it's been 21 hours and it's still tacky feeling. I guess I'll give it a couple more days to be safe.

I'll also check on the body filler, usc fusion, love that stuff. First time I've tried the epoxy first then the filler, always did the straight to bare metal bondo first... trying new things!

Again thanks all !!

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I 2nd at least 24hrs
And reading the tech sheet

 

Uh, is this catalyzed primer that still feels tacky after 21-hours?

 

Maybe tacky isn't the right word, it just feels like it's soft, not cured out yet. Of course in the s.e. corner of Kansas the humidity is pretty high.

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Here in Indiana we can have 90 degree temperatures with 90% humidity. If that's the case double or triple what ever time you normally use. Humidity can slow dry time down.

 

The dry to sand time is overnight which is usually considered about 12 hrs. You are double that now.

Epoxies are usually not that affected by humidity. I would try sanding it and see if it powders up. If not you may have an issue.

 

Thank you guys, it mixes 1 to 1 so as far as mixing it and get ratios right I know I'm good there.

Shot lots of dupont and ppg before, both centari and b/c but this is my first epoxy primer. Everything I've painted has been new parts or oem clean metal, nothing rusted and pitted so always used standard 2k build primers.

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Is that 1:1 primer to reducer?

If so, then it is not catalyzed, just reduced.

A common catalyst ratio is 4:1 primer to catalyst.(hardner), or 4:1:2 primer to catalyst to reducer, to spray as a sealer.

Read your cans and report back.

 

It is a 1:1 mix (primer and catalyst)for that particular product. It has a 24 hr pot life so it probably won't be "hard" at 24 hrs, especially if applied heavy, but is should sand without issue.

 

Minimum 24 hours, longer in a cool or moist climate. You don't want to rush the drying process. Like @Lloyd's paint & glass said, you should be able to sand it dry without balling up the paper. Hurrying this stage has no benefit only heartache and more money and time.

 

@gimpyshotrods yes its a 1:1 primer/catalyst as K13 stated.

@K13 I did 2 med coats, as pitted as the firewall was I seen no harm in it and the TDS said either 1 full wet coat or 2 med coats.

@Bandit Billy you are absolutely correct, I have enough left to do on this project, don't need to add mistakes to the list !

It seems back in the early 2000's and earlier the TDS sheets contained alittle more info then they do today.

Thank you guys for the replies and the answers...

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It should still be sanding without issue at this point. If it's not there is something wrong. Old catalyst, didn't induce it long enough before spraying...

As I said moisture shouldn't really do much to epoxy and the heat should be speeding things up so there is no good reason it shouldn't be ready.

 

Broken record time again.

I refuse to put filler over epoxy primer. Maybe a firewall won't have the recurring issue that finish panels have, swelling of the substrates, but it seems like an easy fail point. I seal and preserve with epoxy, nothing else. It makes a good bare metal corrosion base before surfacing primers. The most critical bonding element to polyester filler is mechanical. It seems maybe 15-20 years ago the latest fashion became filler over epoxy, and why I don't know because polyester doesn't create much of a chemical bond if any at all. And it's in a hot environment being a firewall so theres that too. The tacky feel is normal on mass production price point epoxies. Scuff it with a red pad and give it a day to help purge the trapped solvent and catalyst. To fill, I would scuff it to death to get scratch in the pits 1st, then rough it really good with 80 to get the grip for the filler. The less left under the fill the better.

"Hey man you're full of shit! I've NEVER had a problem!"

There, I said it so others won't have to.

 

Just a heads-up PPG's DP40-LF lists right on the product information sheets that their Body filler is one of the many products to apply over their epoxy primer. I bet PPG doesn't even make Body filler any more ??
Now does that apply to every other Epoxy Primers ?? Well it does for me. I sand with 220 /180 grit dry by hand no DA. to "feel" if the epoxy is fully cured. Never had any and I mean any problems.
yep at least 24hours "cure" time... good luck

 

Just for some clarification " never had any problems " since ????? 6 months , 6 years , 16 years ?

 

https://www.axalta.com/content/dam/NA/HQ/Public/Nason/Documents/TDS/NSN-TDS-491-16-Eng.pdf

 

I’ve done both filler on bare steel and epoxy. No issues with either.
Some epoxies just sand different. I guess some aren’t really designed to be sanded.
New fillers are designed to apply over cured paint/primer with smaller scratches than the old grind with 24/36 to bare metal method. I like the new stuff much better. I don’t miss the heavy grinding.

 

@theHIGHLANDER the firewall had all the holes welded up and all the filler work was done straight to bare metal, I'm old skool too.

I was going to try using icing over the top just to fill in all the rust pits. The pits aren't super deep it's just that there's alot of them but after the epoxy coats and letting it set and flow out I would bet a couple coats of hi build primer is all it will need.

The dash is now epoxy primed but that I am going to try filler over the top.

@K13 went out tonight and it feels hard and dry, sands fine so I'm happy and secure in the feeling that all is good.

I epoxy primed several things, dash, radiator shell, firewall and glove box all at the same time and all feel solid.


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Your doing a repair so you should of did your fill work then prime. If you have a body or panels that have ben stripped you need to get that Bair metal primed with acid etch or epoxy so rust doesn't set in.

 

In 20 years I have never been called about a failure of filler over epoxy that wasn't the result of applying the filler way, way too early or the epoxy clearly stating it wasn't compatible with polyester on the TDS.

 

Another thing. Epoxy sealer sands different than epoxy filler.
Every epoxy sealer I’ve used takes a couple days to sand decently. Never sands like regular primer though.
I’ve never had a product failure that I followed the TDS. I have had em fail when I made up my own rules.

The first car I used filler over epoxy was around 15 years ago. I lightly scuffed the epoxy then applied filler. The epoxy was about 12 hours on the car. We had a new guy helping. He applied some filler over the epoxy with no sanding first.
We scraped at it and couldn’t get it to turn loose and it feathered fine. So we left ot alone.
A couple years later I had to dig back in it because the car was damaged in a wreck. The filler over the non sanded epoxy was hanging on as good as the filler over sanded epoxy.
Car still looks great.
Rust pits and epoxy and a glazing putty?(2 part) No problem. I’ve used a red scuff pad for the pits and a 180/220 over the pitted area. No issues. Engine heat? No problem. Still there. Still looks good.

 

Polyester doesn't like etching primers. There's 1 or 2 specialty products that used to be available, but poly primer or fill over regular etching primer? The poly will peel like Aunt Millies shelf paper. Not now. But likely before you get to color. Get it warm. Like peeling a wrap but stiffer. Metal Glaze or the like is fast set and low volume, and it doesn't seem suffer the fate of full fills.

Hey, y'all do you. I hate having to do it over even more than I've become accustomed to hating it all in general. Mrs O'leary and a cow come to mind.

 

Yeah on the firewall I went from sand blasted, 80grit DA, cleaned, body filler, then epoxy primer.

On the radiator shell, dash, glove box, I went sand blasted, 80grit DA, cleaned, epoxy primer and now I'm going to body filler.

According to the usc fuzion TDS it's compatible over the top of 2k epoxy so I shouldn't have a problem there.

Even though I prefer filler over bare metal how can I pick on you new guys until I atleast try the filler over the epoxy ? so this is a new process for me and I just want to make sure I give it a fair chance.

I really appreciate the replies and experience you gents have given me. I appreciate anything that will help me to do the job right...

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I have been doing filler over primer for about 25-years.

Zero failures of any kind.

 

I'm with Highlander. Been doing filler over bare metal for over 40 years. But now I do it both ways, just depends on the stage of the project I'm working on.