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Old 07-20-2008, 01:01 AM
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Metal Prep before Filler

What is the general thought currently about applying metal prep to an area before filler? I always thought you grind the area that filler is being applied to with 40 or 80 grit then apply filler. Metal prep was used for areas going to be epoxied, stored, etc. I heard of someone using metal prep before applying fillers, specifically in this story, duraglass. just wondering what the thoughts were..

-dennis
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Old 07-20-2008, 03:35 AM
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I've just spent a couple of days grinding 12 year old bondo from a Mercedes Convert. If you saw the rust I found under the bondo you would prep the steel first(phosphoric acid solutions),etch prime then base prime then use bondo . My-self, I can't stand the stuff.
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Old 07-20-2008, 05:12 AM
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throw the etch stuff in the trash where it belongs and epoxy it. always epoxy first.
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Old 07-20-2008, 05:38 AM
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Hi Shine want to explain the difference between epoxy ( trade name?) and any quality Etch primer as used by 99.99 % of every car manufacturer in the world? .I notice on a lot of US based Forums this epoxy primer is mentioned but never explained why it should or could be better than etch primer. No where else in the world have I seen an epoxy primer mentioned. Is it a true epoxy as in it requires a catalyst? or is it just a zinc rich primer with the name "epoxy? "
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Old 07-20-2008, 05:52 AM
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epoxy is a 2 part product. spi is a 1:1 mix. etch primers have failed over and over since they became popular in the early 70's. epoxy will seal the metal from oxygen/moisture . it has a better adhesion and will not shrink or cause die back. unlike the new cars it will not peel and flake off . new car manufacturing can not be compared with repair or restoration work. they are two different worlds. they start with virgin steel that is tank prepped and rinsed but still have adhesion problems. when something comes out of the blasting booth it is cleaned and epoxied the same day here. i use no urethane primers on any of my builds. only epoxy primer. there are many so called epoxies out there but i use spi which has worked great on both vettes and metal .
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Old 07-20-2008, 07:49 AM
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Quote:
Originally Posted by mercmad63
I've just spent a couple of days grinding 12 year old bondo from a Mercedes Convert. If you saw the rust I found under the bondo you would prep the steel first(phosphoric acid solutions),etch prime then base prime then use bondo . My-self, I can't stand the stuff.
I am from the etch works in many cases camp. That is EXCEPT if you are going to use a "metal conditioner" prior to etch priming. You would never do that and if you read the tech sheets, they tell you so. The etch primer IS a "Metal conditioner" of sorts, it has the acid in it that neutralizes the microscopic rust that is on the metal.

Using a metal conditioner prior to epoxy primer could also be wrong, depending on the epoxy primer you are using, read the tech sheets.

If there is no rust on the panel, the filler could be applied over the bare metal as well. This is the norm in the huge majority of body shops and recommended by the filler manufacturer to boot. It may not be the "best" way (over epoxy would be) but it is certainly extremely close to as good.

Factory cars don't use anything like the "etch primer" found at a paint store. It is an "E Coat" and the application is totally different. The metal is different with a Zinc coating right from the start so they are looking at a whole different animal than restoration. If that zinc coating is ground off, yes they recommend an epoxy over it before filler, at least the one manufacturer that I have been trained with, Toyota.

The auto manufacturers change their recommendations like we change favorite TV shows. Where it used to be etch primer, it has gone to epoxy in many cases.

Brian
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Old 07-20-2008, 08:07 AM
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since the auto manufactures have had such a roaring success with their paint over the last 30 years i would surly listen to them i use only 3 products in a job. i see no reason for etch primer since epoxy does a much better job. i've also eliminated the urethane primer in the job. the fewer things to bite me in the bu$$ the better.
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Old 07-20-2008, 08:17 AM
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Quote:
Originally Posted by shine
since the auto manufactures have had such a roaring success with their paint over the last 30 years i would surly listen to them
LOLOLOL, you have a point there!

The last ten or so years they have came a long way. Other than a few hits and misses here and there most manufacturers have a pretty damn good product. Other than on plastic parts I don't see the failures of the eighties.

I do know that the paint we apply at work has a life time warrantee which far exceeds the manufacturers 4 or so years!

Brian
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Old 07-20-2008, 08:30 AM
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Epoxy over clean and sanded bare metal followed by fillers and surfacers provides the best durability on jobs that I've been monitoring since the late 80's. I've also tested with wash primers and etch primers over the years and found the work just doesn't hold up as well. I have a test environment that is probably one of the harshest in the world for corrosion. Shine's proceedure of using the epoxy as the base and surfacer is the absolute best for durability and gloss retension from what I've seen and lately I've been skipping the urethane surfacers as well.
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Old 07-20-2008, 09:02 AM
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Quote:
Originally Posted by baddbob
Epoxy over clean and sanded bare metal followed by fillers and surfacers provides the best durability on jobs that I've been monitoring since the late 80's. I've also tested with wash primers and etch primers over the years and found the work just doesn't hold up as well. I have a test environment that is probably one of the harshest in the world for corrosion. Shine's proceedure of using the epoxy as the base and surfacer is the absolute best for durability and gloss retension from what I've seen and lately I've been skipping the urethane surfacers as well.
Bob, I have planned on setting up a test on the "Magic" rust products like POR15 for years. I have the rusted metal I picked up and all the products to do a head to head test with epoxies and what not. Problem is making a living and family duties get in the way. I have planned on putting these test panels somewhere out on the Pacific coast. But, it doesn't get done.

But as you said, you don't have to go out and do these tests, they come to you!

Have you seen anything by the way of these "magic" products? Have you seen what happens when you use the "Rust coverupper" I mean "Rust Encapsultor" over rust like they say in the instructions?

Brian
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Old 07-20-2008, 10:21 AM
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Brian, I see POR15 as a good product for interior surface rusted areas but on the exterior like vehicle undersides and frames I've seen failures. A few rods that I've worked on were coated with POR on the interior and it seemed to bite good and seemed to provide some good protection on these hard to clean areas. Let's face it if you're working on 20's 30's 40's 50's 60's, era cars there's a lot of bare metal inside that has surface rusted over the years that needs to be removed or stopped. Anything that adhere's and provides a seal will do the job- cosmoline, cavity wax, rust proofing, epoxy primers, paint, rustoleum, POR, tar....


But I have seen people have failures when using the stuff on vehicle undersides/frames/suspension, etc... One early 70's Challenger I worked on was peeling badly after a few years. Rust was running under the loose POR and from what I could tell it looked to be holding moisture-an ideal corrosion environment. Maybe it was user error but the owner said he followed the directions completely using Marine Clean and the recomended etch on clean steel prior to applying the 15. Personally I won't trust the stuff on exterior areas.
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Old 07-21-2008, 02:24 AM
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Down here car paint is subjected to alot more heat and temp changes than in the northern hemisphere and i've never seen new car paint fall off except for clear coats in the mid 80's and those were covered by manufacturers warrenties.
Can you name any paint manufacturers (we have them all here) who make this epoxy primer?
Because the newest vehicles I work on are built before 1980 I have to use phosphoric metal treatment all the time. I'd never rely on my judgment that the metal was oxide free before paint, but i'm always open to others ideas on what works well.
But back to the topic...To use bondo on steel or not?.
I've got a hatred of bondo,I consider it to be laziness not bodywork but if there is a situation that calls for it,I prefer it to be between paint layers. Once an oxidation begins the bondo loses it's bond and falls off or worse, Cracks so everyone can see it and comment...
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Old 07-21-2008, 04:48 AM
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i use spi but doubt you will get it there. as for heat it gets a little warm here in central texas epoxy has proven to be the best product for sealing metal or fiberglass. epoxy resin is best for fiberglass repair. i have never liked any kind of metal treatment simply because it is a gamble from the beginning. if you fail to remove all of it you have problems. dipping sucks for the same reason. we tried that several times over the years and had problems with each car. epoxy will stick when nothing else will . some of the vette guys i know here use "rust defender" by rubber seal (i think) but i have not tried it and most likely wont.
i've seen countless 80's/90's cars here with nothing on the roofs and hoods but a little primer residue.
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Old 07-21-2008, 10:59 AM
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Question for Shine and a few comments.

Shine, you mention you use no urethane primer products. What do you do for a light build, put on a few coats of epoxy? (hopefully I understood what you were saying). I am not saying there is anything wrong with it, just curious.


When I first started learning about painting, I had the local retailer pushing etch over epoxy. I still bought epoxy. Later I call Dupont to ask some questions and specifically asked about etch primer. They were pretty clear in saying that etch primer is only really designed to be a product for use on virgin metal. Etch is for the new metal that has no sanding or sandblasting done to it so you can put the epoxy or other primer down next.

Given the other information about paint failures from improper etch coating and incompatibility with some common products one should use etch sparingly and knowingly.

A little aside.

For those using 40 grit to prep metal for plastic products. Read the tech sheets. Adhesion strength is related more to scratch per inch, not depth. You are better off using finer grit for better adhesion. Several older guys have pointed this out to me. One guy talked about how the manufacturer rep was going to shops trying get the workers to use higher grit papers for better adhesion. This was back in the early 70's.
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Old 07-21-2008, 11:11 AM
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i use epoxy for resurfacing. the 57 vette has 6 heavy coats on it. each was blocked. i do not like urethane primers . not real crazy about polyester. prep for epoxy is 80 grit . i epoxy first then any filler work. resin based products just don't like to bond to acid. we only used it for a short time years ago and promptly dropped it. many guys still use etch and swear by it. same with 2k primers. epoxy/ss/clear just fits my way of painting . i like the way spi epoxy sands and the universal clear polishes with ease. jmho
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