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Bare metal - primer then filler or filler then primer
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Danpa
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PostPosted: Tue Jun 28, 2016 3:17 am    Post subject: Bare metal - primer then filler or filler then primer Reply with quote

I've got the bug down to bare metal and after extensive searching on the net it seems that the opinions on this are about 50/50. Some say over bare metal put filler then primer and others say use primer first then the filler.

The only thing that makes me lean towards filler then primer is that more of the people from that camp state they have been doing it for 20, 25, or 30 years, where the other camp never says how long they have been at it.

Opinions?

Dan

BTW, the car won't need much filler, just a few spots, maybe 1/16" deep at most.
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PostPosted: Tue Jun 28, 2016 6:37 am    Post subject: Re: Bare metal - primer then filler or filler then primer Reply with quote

Well you asked...and I hope you expect to get about a 50/50 split for responses because that is what you will likely get.

Personally I like filler over bare steel. You can put some aggressive sanding marks in it which will give the filler more tooth to bite onto. Filler is a mechanical bond and not a chemical bond. I would then epoxy over that to seal all the metal, then high build, then a sealer, then paint.

Now the other side of the coin is to epoxy primer to seal the metal, filler over the epoxy. Then high build, sealer and paint. The epoxy is tough stuff and will seal the metal. I am just not as comfy with the filler sticking to the epoxy.

either way the repair (if done correctly) will last longer than you own the project.
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raul arrese
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PostPosted: Tue Jun 28, 2016 7:03 am    Post subject: Re: Bare metal - primer then filler or filler then primer Reply with quote

jspbtown wrote:
Well you asked...and I hope you expect to get about a 50/50 split for responses because that is what you will likely get.

Personally I like filler over bare steel. You can put some aggressive sanding marks in it which will give the filler more tooth to bite onto. Filler is a mechanical bond and not a chemical bond. I would then epoxy over that to seal all the metal, then high build, then a sealer, then paint.

Now the other side of the coin is to epoxy primer to seal the metal, filler over the epoxy. Then high build, sealer and paint. The epoxy is tough stuff and will seal the metal. I am just not as comfy with the filler sticking to the epoxy.

either way the repair (if done correctly) will last longer than you own the project.


All good info , you can heavy grit the epoxy before bondo , and then seal it up again as you work , when i did my car i had the car in metal and instantly shot epoxy primer to seal and lock it in then i did all the bondo work , after the car was just about straight i shot it with slicksand and blocked it perfect .
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PostPosted: Fri Sep 02, 2016 10:44 pm    Post subject: Re: Bare metal - primer then filler or filler then primer Reply with quote

Rust sealer (like master series) then light primer, then filler if needed, then high build primer... etc

Doing filler on bare metal is very old school, and there's nothing wrong with it, it's just not quite as good for longevity (due to less sealing of the metal - fillers are mechanical, not chemical, bonds). But it's splitting hairs tbh.

Do it right either way and it'll last a long time.
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PostPosted: Sat Sep 03, 2016 5:22 pm    Post subject: Re: Bare metal - primer then filler or filler then primer Reply with quote

Most of the better quality fillers use both mechanical and chemical adhesion - Evercoat's Z Grip, Rage Gold, Klassen products to name just a few.
Here's what I tell people: If you think it's going to take a while to get all the metal work and filler work done over the bare steel - leaving it susceptible to surface rust and other contaminants - you're farther ahead to lay down a good coat of epoxy primer over the freshly stripped steel.
if you can get all he metal and filler work done in a timely fashion - like inside of a week at the most - you'll be fine doing filler direct to metal. Use a filler that has good adhesion properties and keep the steel as clean as possible and you should not have any problems.

Myself? I like to strip it then lay down a double coat of epoxy. Been doing it this way since the early 90s and have had zero problems. I thoroughly scuff the epoxy with a sharp red Scotchbrite pad before spreading the filler.
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PostPosted: Tue Sep 06, 2016 9:06 am    Post subject: Re: Bare metal - primer then filler or filler then primer Reply with quote

I went to school for AutoBody repair at a well known Tech school. We were instructed to put filler directly on clean, bare steel that had been roughed up with a grinder (36 grit usually). Until.... I took a TOYOTA specific add-on class and their process was to place a coat of epoxy down, hand sand with 80 grit and then apply the filler. The theory was that the filler (known to be a sponge) would be "SEALED" in between the primers. The instructor teaching the class back then wasn't a fan of the process, but we learned it, practiced it, and had great results.

That said....EVERY shop I worked at (until I changed careers) put filler directly on the metal. We completed the bodywork and the it went to the paint shop. Those guys would then spray high build primer and hand block the repair areas. Once the filler/primer work was deemed acceptable, everything else was scuffed/sanded, taped and shoved into the booth for Sealer, Paint, and Clear.

On my personal cars, I put filler directly to the metal (unless its a thin layer of two part glaze to fix tiny little imperfections).
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PostPosted: Tue Sep 06, 2016 9:16 am    Post subject: Re: Bare metal - primer then filler or filler then primer Reply with quote

Seeing cars where bondo has fallen out and the metal under it is rusted on an otherwise good paint job makes me think epoxy before filler is the better choice.
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modok
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PostPosted: Tue Sep 06, 2016 5:33 pm    Post subject: Re: Bare metal - primer then filler or filler then primer Reply with quote

If the filler is near an an edge or seam, or area that will be full of rock chips them I'd put sealer under it.

You should be able to roughly guess areas that need it and those that don't, if nothing else just from how the "before" looked.
Actually a lot of areas you don't really need sealer, if you will be doing high build primer. The high build adheres very well but rust can crawl under if it's chipped.

May be a good use for the little spray cans of two part paint such as "spray max". To paint as you go on spots. In the fridge they will last 3 days or more after being activated. Local paint shop says they can put different kinds of paint in them too now.

I've got rust MOUNTIANS forming around the turn signals on top the fenders. That would be a good example of a spot that often needs filler, and IMO, should have had sealer under it.
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PostPosted: Tue Sep 06, 2016 5:38 pm    Post subject: Re: Bare metal - primer then filler or filler then primer Reply with quote

This has been gone over 1000 of times lol. But if you already have it stripped down to bare metal, DA it real quick with something light to get any surface rust off then epoxy it. If you wanted to do filler over metal and then prime, usually you just work the necessary spots stripping only areas that are needed after you hammer the dent out.(thats how body shops do it). Restoration places media blast the car then epoxy right away to seal it from surface rust. If youre doing it at home i wouldve suggested starting with one peice at a time, body work then priming. The worst you can do is strip a car down then leave it open to moisture.

If youre worried about the filler having adhesion problems to the primer, yoh could always just strip the primer area that needs filler but then youd have to epoxy over it again.

Personally ive never had any problems with filler over primer even after 3 years the cars havent peeled or anything. Most companies would say filler on bare metal because the filler needs the metal tooth to grab to, but some companies are making fillers to go over primer, i cant recall any by name right now but i know there are some companies that say its ok to do so with their product. Most of the time they say to lay the filler over primer within 48 hours or so of putting the primer on. This is so it has a chemical adhesion to the fresh primer as well.
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PostPosted: Wed Sep 07, 2016 4:51 pm    Post subject: Re: Bare metal - primer then filler or filler then primer Reply with quote

EverCoats "blending and smoothing putty" or EasySand states on the container that it is to be put on bare metal like it's other products. I thought that EasySand was a professional type of "glazing putty" (comes with hardener) but the Bondo brand of glazing putty reads that you can put it on any surface. I used EasySand on top of paint with excellent results.It did not crack or fail in anyway through a re-rust out 7 years later in the rust belt capital of NY. The bondo brand is not as physically strong but sands easier and dries a lot faster.

A used car re-seller told me that he tried the more expensive brands of gerneral body filler and did not notice a difference with them. He buys cars at auctions ,makes them look better and re-sells them at auctions. This is his primary skill so I would think he should hold a valid opinion.

On the Bondo company website it states that Bondo Gold uses chemical and physical adhesion. and can be used to fix chips and scratches so this should mean to go right over paint. The the last time I used regular filler over paint it never hardened but I guess the paint was not curred enough. I'm going to do some work on a door later this week and see if the same thing happens with Bondo Gold. Very Happy

If you use filler ,then epoxy and then the repair gets chipped, the moisture/elements can travel through the filler to the bare metal. I do feel that you get a better bond right to bare metal but the bond to primer/paint is good enough.
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63 vwnotch
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PostPosted: Tue Sep 13, 2016 5:13 pm    Post subject: Re: Bare metal - primer then filler or filler then primer Reply with quote

theKbStockpiler wrote:


A used car re-seller told me that he tried the more expensive brands of gerneral body filler and did not notice a difference with them. He buys cars at auctions ,makes them look better and re-sells them at auctions. This is his primary skill so I would think he should hold a valid opinion.

On the Bondo company website it states that Bondo Gold uses chemical and physical adhesion. and can be used to fix chips and scratches so this should mean to go right over paint. The the last time I used regular filler over paint it never hardened but I guess the paint was not curred enough. I'm going to do some work on a door later this week and see if the same thing happens with Bondo Gold. Very Happy

.


yeah the used car salesman really cares what happens to the car after his 3 month warranty is up..( but in this case there is no warranty because he resells them at an auction never even meeting the buyer) his "valid opinion" as you call it, is as good as a $3 bill. Bondo brand is junk!!! look up spec sheets and compare apples to apples Bondo Brand Homeowners special should be left where it belongs, the play ground...

Most quality epoxy primers spec a minimum of 80 grit adhesion on substrate, do "not" sand your bare metal lightly as previously mentioned before you apply an epoxy primer unless of course the manufacturer calls for it, which I have yet to see... not a professional by a long stretch but I've painted a lot and have always used Bondo over bare substrate..

I have used Evercoat rage gold for a long time this is news to me putting filler over primer I will have to dig into this more as it does sound very appealing...
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PostPosted: Tue Sep 13, 2016 5:57 pm    Post subject: Re: Bare metal - primer then filler or filler then primer Reply with quote

All repairs that remove the Electro Paint or Zinc re rust fast. Exotic cars have their quarter panels repaired multiple times and I doubt they are driving the car in the snow. I have used EverCoat and Bondo gold on the same panel and besides for a re rust out neither product showed signs of failure in anyway, no cracking shrinking etcetera.This was about 7 years later in NY where they dump a pile of salt at every intersection.

If the hoopty dealer can make it look good the repair is not going to look any different until there is enough salt spray to cause rust again.
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PostPosted: Fri Sep 16, 2016 12:01 pm    Post subject: Re: Bare metal - primer then filler or filler then primer Reply with quote

May I suggest following the manufacturers procedure. All paint companies recommend a certain procedure & products for each step of the repair/refinish process.
Yeah I know read the instructions before starting.
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PostPosted: Sat Sep 17, 2016 7:02 am    Post subject: Re: Bare metal - primer then filler or filler then primer Reply with quote

I've been doing this a really long time and have had good luck both ways. Seems like I read where someone actually did a test and filler held best over primer sanded with 80grit. I expected primer sanded with 36 grit to be stroger because of the superior mechanical bite, but it wasnt. I believe it was a bit better than filler on bare steel though.
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PostPosted: Sun Sep 18, 2016 8:19 am    Post subject: Re: Bare metal - primer then filler or filler then primer Reply with quote

I agree with Buguy, in that I've done it both ways too. I personally prefer to lay down epoxy primer 1st though, as it seals the metal (I live in the rust belt). I've also used Rage and Rage Gold over epoxy with good results out of both. About the only time I use filler over bare metal, is when I'm using All Metal or Metal 2 Metal filler, as it seems to work very well there.
I should mention that I've been using filler over epoxy since 1990, and rarely have I seen it "pop" loose (no mechanical grip to the epoxy). Now, if the vehicle has been subjected to winter salt use, and not washed regularly in the winter season, I've seen it fail, but most times there'll be rust behind it from where something failed (similar to just putting filler over bare metal). This is usually 5 or more years later though. However, I've seen rust form around areas that were just filled over bare metal more often, but these were mostly body shop repairs that were insurance jobs. But, I've also seen where someone did a "mop and go" to make more money on a vehicle (it's the new owners problem). Do this sort of work long enough, and you'll see most everything. Just my take on it. YMMV.
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PostPosted: Tue Oct 04, 2016 11:40 pm    Post subject: Re: Bare metal - primer then filler or filler then primer Reply with quote

I had to revisit this thread after reading this..
http://autobodystore.com/filler_&_epoxy.shtml
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PostPosted: Fri Oct 14, 2016 7:29 pm    Post subject: Re: Bare metal - primer then filler or filler then primer Reply with quote

That is cool test.
However, note he used DP90-LF epoxy primer.
This is WEAK SAUCE primer, not supposed to be strong.

AND bondo cracks, nothing you can do to stop the cracks, but you can stop the water from CRAWLING under it and rusting, which is what the primer is for.

SPI recommends filler over epoxy, and they say their epoxy is resistant to gas and even DOT3 brake fluid, while DP-90lf is reported to wipe off with solvent. Re-do the test with SPI primer Wink
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63 vwnotch
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PostPosted: Fri Oct 14, 2016 10:24 pm    Post subject: Re: Bare metal - primer then filler or filler then primer Reply with quote

not familiar with SPI primer but than again I've been somewhat out of the loop a bit, and was even forced to use SW on a jeep lately, personally I've had good results with PPG...

SPI ships free, outstanding as I doubt there will be a jobber here locally
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PostPosted: Fri Oct 14, 2016 10:57 pm    Post subject: Re: Bare metal - primer then filler or filler then primer Reply with quote

I LOVED the old PPG DP epoxy. It was gummy and a PITA to work with, but it stopped rust dead. Unfortunately, what made it work was lead chromate, and ever since they took that out it never was the same at all, and you will hear the same from everybody.

I don't think there is only one right way to do things, but I do believe in using a good primer. You should see the rust bubbles growing on my car Shocked It's got to the point of an emergency, I HAVE to repaint some areas of it before winter, wish they had put some of the good stuff under this lovely pearl paint. I did re-paint the rear apron 6 years ago, and used a lot of filler, and 30% of it fell off, but it isn't rusting Laughing Nothing is forever.
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PostPosted: Thu Oct 27, 2016 1:09 am    Post subject: Re: Bare metal - primer then filler or filler then primer Reply with quote

https://www.youtube.com/watch?v=-yA8q4K-_Bo
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