Doing work with body filler.....

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77tagoldenrod:
Quote from: "JasonD"

Do you put body filler on bare metal or do you put it over primer?

I say you put it over bare metal and bare metal ONLY. I've had this arguement with people MANY times over the years. It seems that even though I've been working with body filler for almost 20 years some people would rather listen to some paint guy on the phone or some teacher at a technical school who couldn't make it for real in the industry. I even had a dude tell me he saw the guys on Boyd Coddington's TV show put filler over primer. Personally, after watching that show, I wouldn't let some of those goons get within 10 feet of my car.

I've been around this stuff for a long time. I know that it like to stick to clean, sanded steel like crazy.......but nobody wanted to believe me.

Well some dude decided to do a real world test to see what would happen when you put filler over sanded steel or primed steel. He wanted to see which one was stronger. I knew the results of this test even before I saw the whole page.....but it's GREAT to see somebody come up with a little proof for the pudding.

Check it out:
http://www.autobodystore.com/filler_&_epoxy.htm

And don't forget.....filler over CLEAN, BARE, SANDED STEEL!  8)


I went to a technical school from 1984 to 1985 for Auto Body.  At that time, my two instructors had over 55 years combined experience in the real world, retired from active body work, and went into instructing.  After realizing there wasn't many good jobs out there for Auto Body repairmen I decided to go to war with the USAF during the first Gulf War.  Glad I did because now I have a family and a very good career as a Computer Programmer/I.T Project Manager/Business Analyst.

Anyway, during Auto Body training, we were never taught to put "Bondo" over primer.  We were also never taught to put Bondo over bare metal.  We were always taught to put Bondo over properly prepared surfaces.  We first learned repairs by fixing an AMC Matador fendor that was donated to the school.  Don't know how many remember a Matador but that was a big fender.  We were instructed to fill a dent with Lead, a small dent with no filler, only heat shrink, and then a larger dent with Bondo.  After everyone was done, the instructors went around and nailed the center of the fender with an aluminum baseball bat.  Anyone whose repair area's failed, started over.  I remember specifically, my bondo repair was over bare metal and passed,  my friend in school did his repair over dupont primer.  His also passed.  Others failed under both situations.

During my midlife crisis (NOW), I decided to purchase a trans am and do a restoration for old time sake.  One of the first things I did was pull the drivers fender, lightly tapped the back side and off fell 3/4 inches of Bondo.  Low and behold it was primed underneath, not sanded, and rusting through into the Bondo.  No idea how long it had been sitting there but it definately didn't hold.  On the roof of the car was a light coat of bondo to fill some small dents behind the windshield.  Over primer, over paint, not sanded and that stuff just would not come off after tapping from inside the car.

All I'm saying is, unless things have drastically changed with the characteristics of filler in the past 23 years, any properly prepared surface will hold Bondo to pretty extreme conditions if the manufactures directions are followed to the letter.

Painting on the other hand has definately changed.  Holy Cow.  What Ever hanppened to Dupont Centari.

PS.  Boyd Coddingtons crew isnt going near my scooter let alone a vehicle of mine.

norwood:
When I started doing body and fender back in the early 70's we were taught to put filler over bare metal that had been roughed up with a 36 grit disc.

CJK440:
Interesting test, I saw that before and it didn't sway me. Not necessarily a real scientific one but it does illustrate the point that if you do body work on a demo derby car and want it to look as good as possible after being smashed up, then definately go over bare metal.

If my body work gets dented, bent or attacked with a screwdriver then does it really matter??

I use filler over epoxy and while I won't disagree with other opinions, there is no doubt in my mind that it is sufficient for my use.

I had a mistake that was a good real world test. My T/A suffered a fender dent in storage. A thumbnail size chip of filler popped off but took all the epoxy with it. Therefore the epoxy to metal bond was the weak link NOT the filler to epoxy bond. Had the filler been over bare metal, it might not have popped, but no matter what, I had to strip the fender, tap the dent out and start from scratch.

The main reason I prefer filler over epoxy is because poly filler absorbs water. Moisture against bare metal is bad. Epoxy acts as a barrier coating. A rock chip in the lower rear 1/4 could let moisture infiltrate the filler and wont play nice with the steel.

But in the end, I think for the pampered lives our cars live, either is a good option.

gregh:
Quote from: "JasonD"

Do you put body filler on bare metal or do you put it over primer?

I say you put it over bare metal and bare metal ONLY. I've had this arguement with people MANY times over the years. It seems that even though I've been working with body filler for almost 20 years some people would rather listen to some paint guy on the phone or some teacher at a technical school who couldn't make it for real in the industry. 8)


Jason how old are you?

xtrme_ta:
Quote from: "gregh"

Quote from: "JasonD"

Do you put body filler on bare metal or do you put it over primer?

I say you put it over bare metal and bare metal ONLY. I've had this arguement with people MANY times over the years. It seems that even though I've been working with body filler for almost 20 years some people would rather listen to some paint guy on the phone or some teacher at a technical school who couldn't make it for real in the industry. 8)


Jason how old are you?


Man you just made me realize how old I am. I bought my first car and restored it at 13. So that gives me 27 years doing this stuff. I also spent a few years helping out my brother before I turned 13.
I think I need a new hobby.

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