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filler primer or self etching primer

john mcgarvie

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OK i have already sanded my car down to metal and painted it with filler primer. But i was told that if i go to bare metal then i have to use self etching primer.Therein lies a problem I'm i have already painted it will i have to sand it all off? I'm wondering what will be the effect of just using filler primer.Also wile i have a professional reading this the URL is the paint I'm using please give me input on it.



Edited by john mcgarvie
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Hi there, I can't give you much advice but the body shop that is painting my car used the self etching primer. I had the car dipped so the entire shell was bare metal. I will try to contact him and ask.


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That sounds good getting the car dipped but I'm a little past that stage. I just have to say hats off to any one that dose the hole car and dose not take shortcuts every time i look at it i find something else.I'm back tracking . This car is going to be my sons car and I'm doing one for me next.

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I finally heard back from the body shop. This was his reply: "The only filler primer that adheres well to bare metal is polyester primer. other primers have a tendency to peel when sanded if sprayed only over large bare metal surfaces. hope this helps." I don't know what polyester primer is but that what he says. Hope this helps.


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OK i have already sanded my car down to metal and painted it with filler primer. But i was told that if i go to bare metal then i have to use self etching primer.

Normally, if you have sanded the old finish off, down to bare metal - you have also all but polished the metal itself. You can use either a self-etching primer such as many of the epoxy primers are, or you can use a chemical such as Ospho to kill flash rust and etch the metal, then prime. Many Body Shop Supply Stores sell chemicals that can be added directly to some primers to make it a one step process.

Therein lies a problem I'm i have already painted it will i have to sand it all off? I'm wondering what will be the effect of just using filler primer.Also wile i have a professional reading this the URL is the paint I'm using please give me input on it.


Sounds like you already have an answer to what could happen - the paint and the primer it is adhered to can peel off in sheets. Just because it "can" doesn't mean for sure that it "will". If the car is still completely apart.... only you can decide if you want to take the chance or not. If the car is already reassembled.... you've pretty much already taken the chance.

I've never used that brand of paint. I will say that looking at the cost of a gallon of their Acrylic Enamel Red or their Urethane Base/Clear .. it seems awfully cheap... When it comes to Automotive finishes you usually get what you pay for. Granted there is a large difference between wholesale and retail.. but even at wholesale prices premium quality finishes usually cost three to four times that much.

Are they worth it or not - again it depends on your objectives/goals. In terms of lasting finish luster and durability IMHO the answer is yes.


Carl B.

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Yes, you need to use etching primer. I would take it down to metal and start again. It reallly sucks but if you have gone this far do it right.

I also agree that with auto finishes, you get what you pay for. I hate it when people spend tons of money on their cars and skimp on the paint.


I have never heard of an epoxy etching primer. I could be wrong as I am no expert but I have been doing paint work for 6 years now and have never seen it.

I painted the hood of my 510 with PPG ethcing primer after taking it down to metal. I used very light coats and it dries translucent green. Then I sprayed the hood with PPG black epoxy primer which is also water proof.

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Hi Brandon:

I'm certainly no chemist nor expert on todays painting systems... but as I understand it - from the people I know that are in the business........

First - just to be clear. I said self-etching epoxy primer. I did not say "epoxy etching primer".


n. pl. ep·ox·ies

1. Any of various usually thermosetting resins capable of forming tight cross-linked polymer structures characterized by toughness, strong adhesion, and low shrinkage, used especially in surface coatings and adhesives.

Epoxy Primers are commonly said to be self-etching - Common use however does not agree with the technical definition of the term "etch" - Granted.

Epoxy primers that contain a fairly large amount of solvents, actually soak into the bare metal surface... and they are commonly referred to as being "self-etching", meaning they do not require bare metal to be acid etched prior to application, nor do they require an etching agent to be included or added.

BTW- epoxies of all sorts make excellent adhesives because of their ability to penetrate and thus bond themselves to the surfaces to which they are applied.

According To DuPont For Example:

DuPont CF-22860S Chrome-Free Etch Primer is a is a two-component, self-etching primer that provides exceptional corrosion resistance and adhesion to properly prepared bare metal (steel, galvanized and aluminum). It is mixed 1:1 with 22805S ChromaPremier Activator

DuPont 2510S Epoxy DTM primer-sealer a two component primer with corrosion resistance and excellent adhesion for direct-to-metal applications. DTM is available in lead/chromate free and chromate for use under body filler, polyester putties, primer-surfacers and topcoats. It is mixed in various ratio's with DTM Activator

The primer you are using most likely is a zinc chromate primer, they usually dry out a light green. {but that is just a guess on my part}. If it is a two part - ie mixed with an "activator " prior to application it is an epoxy. If it is sprayed out of the can and simply mixed or thinned.. it is not an epoxy.

Sorry for any confusion of terms .... Please feel free to correct/discuss/disagree... as I said, I only go by the "in shop" education my friends supply as I constantly ask questions. Both my friends have 30+ years experience in body shops, both sell automotive paints and supplies, both are excellent painters themselves - and one is paid by several different paint manufacturers and suppliers to demonstrate proper use and application of their products - in body shops around Florida and at trade shows Nationally. NEITHER however are Chemists, so I usually get mixed terms from them, with lots of "ifs", "and/or's" and "except whens"..


Carl B.

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Damn Carl!! You are like the human wikipedia :) You and Riley Curtis both. I never delete any of his e-mails.

I see what you meant. I think we are all on the same page now.

I am also only educated by the painters I know. I generally pick their brains as I work on various projects and slowly but surely increase my knowledge on the subject.

Thanks for clarifying these definitions :)

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Ospho is a mild solution of phosphoric acid. DoD tests from decades ago and more recently repeated have shown that a phosphoric acid wash on steel is the most effective method of controlling oxidation while at the same time etching a smooth metal surface.

By a chemical action phosphoric acid converts iron oxide to iron phosphate. Iron phosphate is inert. It is important to allow enough time for the acid to complete its chemical action however, before cleaning any residue off. For bare metal that is freshly sanded, that can be as little as an hour. Then it can be washed off with water, dried and primed. Water??? Yes, a water wash will not cause rust to form on top of a bare metal treated with a proper acid wash, followed by being dried off {blown dry with compressed air or dried with a heat gun}. You just don't want to leave an acid residue under your primer/paint.

Other than the epoxy primers, automotive primers are not vapor/moisture barriers. Nonetheless if you washed the metal down with Ospho, then primed the surface - 3 weeks should not present a problem if the car was not subjected to rain or sitting outside going through thermo cycles. Matter of fact you want to allow time for any "bondo" type epoxy body fillers to completely cure/dry. {meaning all chemical action has stopped between the hardner and filler}.

When you see body fillers bubbling up under a paint job - - six months to a year after the work was done - highest chance is that the body filler wasn't allowed enough time to completely cure in the first place.


Carl B.

Edited by Carl Beck
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  • 3 years later...

Hello Carl & Gaggle:

I was doing some searching for primer information and your site came up. After reading the question and the posts it seems like Carl is the GOTO guy.

I am not rebuilding a car, I am rebuilding a plane. And I know next to nothing about painting and even less about painting ALUMINUM.

So, here are my questions/information:

1 - In the old days, yes, I'm almost as old as dirt. DuPont produced a product know as IMRON, it was the best stuff for planes, but, thanks to the all knowing EPA it is no longer available. Oh, yes the NAME still exists but the chemistry has changed. The plane I'm working on has some of that old paint. GAUD it is still bonding after 40 years. I would like your opinion on whether I should strip it or not... MY FEELING IS NOT! HELL, IT HELD ON FOR 40 YEARS.

2 - If I do not strip I would like to know what primer I could use to do the following:

a> Bond to bare Aluminum.

b> Bond to the preexisting paint - Note: There is NO topcoat, no wax and the paint has been washed many a time using soap & water with RED SCOTH-BRITE PADS. Also note there is some Bare Aluminum and some MUD CRACKING.

c> I would like to use a PRIMER that will ETCH and bond to Bare Aluminum - Painted Aluminum - ABS Plastic - 4140 Steel (Rust-able iron). AND FILL the Mud Cracks.

PLEASE NOTE: I am NOT looking for a showroom finish. The plane is going to be painted is a very light gray - 3 shades darker than white with military markings. Lets say I want a 25 Foot paint job. PROTECTION is the goal, with a slight sidestep to LQQK's.

4 - Carl, from your writings I gather there is no such thing as SELF ETCHING EPOXY PRIMER. Well, here are some more of my requests for a primer:

a> It should fill the Mud Cracks

b> It should be SANDABLE - Yes, I will sand the primer to get the best finish - Or a finish I will be happy with. I was going to use 320 Wet/Dry (WET). I'm only a little lazy but very cheap when it come to 100% stripping.

5 - TOPCOAT - AKA Base Coat - Will be a Urethane. As stated the color will be a light gray, so the Primer should be something that will contrast with the gray.

There will be NO top coat. I will be waxing the plane but WEIGHT of the paint is a factor, so the WIGHT of the paint is a factor.

OK, that covers about 95% of the basics and my crazy requirements. Can you HELP?

Thanks you Carl & Gaggle?

BTW - Gaggle is a Formation Flight of different planes.


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