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Bare Metal Prep


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I am restoring a 38 Buick Coupe. I have it stripped to bare metal. I have minor surface rust and before priming the car I have been told one can use Rustoleum to the only thing to use is PPG SV epoxy primer. Can anyone shed some more light on this?? Thanks in advance.

Bill, Dayton, Ohio

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The first question is what brand of paint system are you going to use. If Dupont, or PPG, or what ever, the first thing that I would do is to contact the supplier and ask them what kind of metal prep that you need to use that is compatable with their paint. Sometimes using one of the steps of material from a different supplier will cause problems with the final paint finish. Try to do the paint job with all of the materials from the same manufacturer for the best results.

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What I use is a product called metal prep and it's a acid solution for etching the metal. After that wash it down with water to neutralize it and dry it fast (all of the water & metal prep must be gone), then spray epoxey etching primer to seal the metal. After all of that you can apply your sanding / filling primers and begin blocking the body and after that paint.

D.

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Thanks Mark I will make a note of that. Doing it the way I described you've got to move pretty fast so I'm just doing sections at a time because it flashes pretty quick.

Don

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Surface rust must be removed.

This can be done mechanically with sand paper or chemically with products like Ospho, Pickle X 20, or several harder to use rust removers. Ospho and pickle X have the advantage in they do not need to be washed off are application. Some the systems you get from PPG or Dupont are multi step processes.

You really want to get an epoxy primer direct to the metal as soon as possible. The only exception is if you need to work the metal or put in a patch panel. I used Pickle X on my metal and it kept the rust away for a very long time. It is interesting to note that some parts that I did not heavily blast the rust pits I found the rust was not cured by the pickle X and the rust reappeared.

I suggest that you look up SPI paints. They are cheap and effective. You do NOT need to stay with all one brand of paint. The key is to read and follow directions on surface prep. Always keep in mind many paint failures are from improper pre-paint applications. For all paint understand what the recoat window means. That is the time the paint is open for accepting the next layer of paint or in the case of epoxy, when you can layer in bondo on top without sanding. If you go past the recoat window then you must sand or scuff the surface.

It is winter time. You must not allow epoxy to fall below the recommended temp while it is curing. Keep in mind the metal temp is what you care about. Just because the air temp is 60 does not mean the metal is that warm.

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  • 2 weeks later...

I really like helfen's response, that is how I learned. Get that epoxy primer on there to act as a binding agent.

One thing is for certain: if you ask 10 experienced body men, all of whom have turned out outstanding work, how to so this, you will get 10 different answers, each one absolutely "the only way".

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Hi-I'm one of those body men who does restoration work on a daily basis. I think you need to clean the body of all surface rust mechanically or with a derusting treatment such as Ospho (which I have used very successfully). Even if you sand off the rust, a treatment with phosphoric acid (Ospho or similar products)will clean up the surface, etch it, and make a great base for epoxy primer-one of the best bare metal treatments. Once the panel has been cleaned with phosphoric, it should be washed with a wax and grease remover, wiped , then primed.It should be primed immediately so you avoid surface contanination which can occur to bare metal sitting around in the open air. The DuPont procedural manual recommends 2 coats for protection against moisture while the car sits in primer.

The car can sit in primer for fairly long periods of time while you do other things to the car or it can be immediately overcoated with a sandable primer which is my normal prodedure. There is no need to resand the epoxy primer before overcoating with sandable primer sol long as you spray with a 7 day window. I try to overspray the same day due to concerns about surface contamination.

I don't think you'd find that much difference among paint professionals as there are published procedural manuals for bare metal painting and most paint vendors are sellings the same basic products with some trade name such as Centari(acrylic enamel).

My suggestion if you are going to paint your own car is--- get a vendors paint procedural manual and the instruction brochure for each specific paint product (epoxy primer, etch primer, 2K sandaable primer, sealer, etc.) you buy and follow the suggestions religiously.

Painting without these directions is like doing mechanicial work without a specific shop manual for that car.

Martin Lum

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Martylum is correct I am a body man also and the prosedure Martylum is the correct procedure for excelint prep work.you should have two cleaners , one for water born contaminints such as swet ,bug juiceand such and one for oil base contaminints such as grease, oil, swet. etc.then etching primer, than an ecoat some etching primers act as ecoat also than a sandable primer . the the reasoning for so many different primers is the etching primer is desined to stick to the metal , the ecoat is to protect the metal and provide a good base for adheasion, and then the epoxy sanding primer sticks to the ecoat . of corse if you are on a budget you could leave out the etching primer and spray the epoxy primer right on the metal. but the paint manufacurer might not warrenty the paint. and theses extra steps will insure a long lasting paint job. So get to work I want to see it done in a week like on TV. LOL

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Martylum--my comment was partly tounge-in-cheek, I do know some body guys who swear that body filler should be put directly on bare (blasted/prepped) metal. I happen to disagree quite a bit with that, but they are firm in their assertion that their method is the only way. I much preffer your methods.

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The replies #10 & 11 above are pretty accurate about correct bare metal treatment before finish coating. I do my own restoration preparation and know after moving from Chicago to a rural area not all the right stuff is on a shelf near you in certain areas.

I have used these two cleaning products with good results Dupont 5717S and PPG DX579 to prep older (1920's) metal parts where rust is well established and grinding all pits out would remove a lot of good metal along with the bad.

Another item for small areas I learned about from another restorer is Dupli-color DAP1690 self-etching primer, it is expensive but gives good results.

Stude8

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If I read this correctly

1) Once the metal is blasted,

2) washed down with a degreaser

3) epoxy prime, 2 coats

4) Sandable primer, one coat or two?

5) wash down

6) paint

My questions

A) When does one add any filler if needed to fill the pits, small dents, ect?

B) What filler would be recommended.

I was also thinking of using POR 15 on the undersides and the inside floor painting the Por 15 as a top coat. Any comments? Please?

C) Am I thinking along the correct lines?

Skip

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My understanding of the use of the various acids to treat bare metal goes like this. Some acid products remove surface rust and etch bare metal. Some acid products remove surface rust, etch bare metal and STOP further rust action with a conversion process. After 80 grit DA sanding and producing grinder scratches where I know filler will be used, I treat all exterior bare metal panels with the conversion type ( SEM RUST MORT ) because I know it will stop the extremely small unseen rust bits that DA sanding with 80 grit or grinding will not completely remove. This is extremely important because the rust will re-bloom sometime later if not stopped now. I think applying etch primer to a chemically etched panel is a waste of time and material. I also think that etched panels should not be cleaned with anything prior to priming unless it is certain that they have become contaminated. Why introduce another product and procedure to a panel that is prepped to the max already? The panel/car should have been throughly cleaned before any work was started. Properly used etch materials don't produce contamination. I usually next spray the panels/car with 2 coats of PPG DP epoxy primer mixed with the slower activator and the recommended amount of reducer. I feel that this mix of primer components allows a slower dry and therefore allows the primer to penetrate the microscopic pores of the metal for best adhesion. I've used a fair amount of RAGE EXTREME filler on bare metal as well as over epoxy primer and it works well. I'm using this procedure now on a 1940 Ford that will be painted with Glasurit urethane acrylic black.

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SKIP, If you are referring to abrasive blasted metal I suggest thoroughly cleaning and degreasing the parts prior to blasting as the blasting can drive the contamination into pores in the metal as you strip the part. In quick succession clean with clean compressed air only and follow immediately with epoxy primer before flash rust can occur. Now apply filler ( I use Rage Extreme ) if needed. Sand. Prime. Sand. Clean with PPG DX 320 or Dupont 3812S or equivalent not wax and grease remover. Tack wipe. Color. I've used Por 15 on floors and like it.

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