The Stovebolt Site Forums The Shop Area Paint and Body Shop How to prep pitted sheetmetal?

I've never had to deal with anything pitted as bad as THIS.

What is the best way to prep this mess before priming? I'm going to do the best I can to get all the scale out from the pits, but there are umpteen million of them and I want to finish this door before the 22nd Century.

I'm thinking a good washing with phosphoric acid?

Any help will be greatly appreciated.

BTW, Sandblasting has to qualify as THE most boring thing I've ever done in my life. No wonder they charge so much!

Czechman, that looks like the pits are into the metal and I don't think you can sand, grind, or blast the metal enough to allow you to level it out with primer. I know Por 15 will cover up a lot of sins! Sorry I don't have a good answer for you.

clean it and skim coat it with finish filler then use a hi biuld primer and block sand it smooth you could wash it with ospho

I understand that I'm going to have to fill the pits with a high build primer or a skim coat of something like "Icing" over the primer but what I want to know is what do I prep the metal with before I spray any kind of primer?

Normally I just go for the self etching primer first but I'm concerned that any particles of rust down in those pits may come back later to bite me.

Ive had good luck with Eastwoods Rust Encapsualtor, It is pretty thick and can be thinned and sprayed as a high build.
From what Estwood says there Ecapsulator seals out all O2 to keep any remaining rust from being able to grow ???
Just a thought

Well Woody I gotta cast my vote with Joe here, ya gotta get ALL the rust out. It makes no sense to go through all the work and expense of painting and have it come back to bite you in a couple of years.

If it were me, I would definitly use a chemical to get all the rust out of the pockets/pits. Encapsulating the rust just seems to me to be a band-aid except in this case the wound tain't gonna heal up.

Metal prep or metal conditioner, i.e., phosphoric acid looks like a must and don’t skimp, use a conversion coating after the conditioner. Better yet this would be a perfect candidate for chemical dip if there was one near you. I just ordered a Copy Cad kit from Caswell and I asked about removing the old plating from the parts. They recommended using a 50/50 Muriatic acid (weakened hydrochloric) bath to remove it and any rust. You might try that in small area and inspect it with an eye loupe after cleaning if the metal prep doesn’t do the job.

Sand blasting is out in my opinion, it isn't going to get down into the very smallest pits unless you blasted away everything around the pit, its just air sanding you know. Of course if you did blast by the time you got to the bottom of the pit the metal would probably be warped in the flat areas.

You got the build up all figured out so no need to say any more on that. Just one thing on the acid etch primers. Don’t get lulled into thinking that this is what they are formulated for, they are all too often misused. They are designed to be used on the new metal that has a galvanized coating not for bare steel. Just read any of the spec sheets from any of the paint manufactures. There is no need to use an etching primer on bare steel if it has been prepared properly. That would be with Metal conditioner and a conversion coating.
Denny Graham
Sandwich, IL

Have you given any thought to THIS method?

I had originally planned to submerge the door in vinegar to rerust it until I calculated that it would require 60 gallons so I opted to spend the money on a sandblaster. It's still cold here and it would have to sit for a very long time for that to work.

The door is too large to submerge in any liquid and the nearest place that dips parts is 200 miles away... I'm sure there are ways to do this. I've seen some of the hulks guys have pulled out of fields.

I second the motion on the Eastwood Rust Encapsulator. Try to remove the rust but when at last you have done as much as you can to rid the rust then use the encapsulator.

I'm not sure what you mean here. Can you please explain what you mean by "conversion coating" and "conditioner"

Thanks!

Woody ,
I would think "Conversion Coating" would be the stuff that been around a while ya spray or brush on and it converts rust to a black coating .
Om my 52 I had some nasty surface rust around the windshield where the gasket was holding water & being I couldnt blast it ...since I didnt have my Cab stripped , I cleaned it up as best I could by sanding , I then used Eastwoods Rust converter it is a 2 part system ya mix 50/50 as much as you need & brush it on , the rust turned to a hard black finish after that cured I brushed on there Rust encapsulator all around the gasket area ...came out really nice ! . I hope that it will keep it sealed and I WONT HAVE ANY FUTURE PROBS.
Tim

the stuff called ospho is sold in paint and harware stores it acid mixed already like 5 bucks a bottle its blue liquid i put it in a small spray bottle but you need to have the door striped or blasted clean for it to work good same with any acid and spay it with a spray bottle it will bubble up and will get a white powder and black scales after this you will need to use some kind of metal clean before primering but if you leave it in the air rust will start returning but if you have it in a shop you can get it sanded up pretty good and clean before primering

Arm and Hammer sells a product called washing soap - it is Sodium Carbonate - not confused with backing soda which is Sodium Bi carbonate. Mix it with water tablesppon per gallon something like that - on diections. It was on a previous episode of Trucks I believe. Replaces use of acids etc. and is a method of electrolosis using batterry charger as well. I have used it removing cacalcium carbonate from metal object recovered from underwater.
Cavebull

Rather than me try to explain it take a look at this: http://www.performancecoatings.dupo...info/chromasystem/H-19288_SurfPrepOV.pdf
This just happens to be Duponts system, all of the other paint suppliers also have similar products.
Another discussion on the two part cleaning process: http://www.chevelles.com/forums/showthread.php?mode=hybrid&t=10291
And another, there are literally hundereds of these that discuss the proper way to prep bare steel for finishing.
http://forums.performanceyears.com/forums/showthread.php?t=442307
These are not rust encapsulating products or methods, they clean the metal to bare metal and prep it for finishing. I am not an advocate of leaving the oxidation on the surface and just covering it over!
Denny Graham
Sandwich, IL

Okay, out of this confusion I believe treating the bare metal boils down to two possible courses of action.

1. Go through the Metal Prep process of cleaning the metal with acid, with the washing, scrubbing, wiping and cleaning.

OR

2. Skip all that mess and just apply a coat of self etching primer over the blasted and cleaned (as in remove all the residue and fingerprints) bare metal.

If you can simply use self etching primer WHY would anyone even bother with the acid process?

Can something so simple possibly get any more confusing?

"etching primer" doesn't neutralize any rust, just makes better 'tooth' for the next layer, the rust will come thru eventually - a rust converter will work, and some can be primers - an ecapsulator can also work, especially if they're at least partially a converter, but I prefer to use the phosphoric acid as a 'converter' to eliminate the iron oxide and the oxygen that will be entrained in it, leaving iron phosphate to protect for a short while - begin coating as soon as dry, heat guns help

Bill

Maybe ya just missed this earlier Woody, but here it is again;

"Just one thing on the acid etch primers. Don’t get lulled into thinking that this is what they are formulated for, they are all too often misused. They are designed to be used on the new metal that has a galvanized coating not for bare steel. Just read any of the spec sheets from any of the paint manufactures."

When you use an metal prep to remove "light" rust you just can't leave the resadue on the metal, you need to wipe it down after it has done it's job. Your objective is to desolve the surface a few microns deep and leave clean bare steel.

Etching primer is used to give the galvanized surfaces tooth for the primer to grab on to. The bare zinc coated metal still needs to be clean before applying the etching primers. Forget the etching primers for what you are doing!

Another explanation of Metal Prep from Metal Web News, I quit after this;
“Another technique for removing rust is etching with Phosphoric Acid. Phosphoric Acid has a unique property of dissolving iron oxide quickly while etching iron very slowly. This means that you can leave metal in Phosphoric Acid for much longer than necessary with very little damage. The acid will attack bare metal slowly and will start the process of hydrogen embrittlement, so use the minimum etch time that removes all rust.
Another unique advantage of Phosphoric Acid is that it leaves a fine coating of iron phosphate behind. Iron phosphate prevents rust. However, the iron phosphate coating is not very thick and not durable. Some additional protection is still required.
Phosphoric Acid etch will leave a hard, bright metal finish. This is because it will etch the surface slightly, exposing new, bare metal. Often this is desirable. It leaves an attractive surface and a surface ready to paint. A common product which contains Phosphoric Acid is Naval Jelly. The soft drink Coca-Cola contains Phosphoric Acid, so Coke will etch rust. But Coke also contains carbonic acid and other nasty things. You're going to drink that stuff?
Auto body shops treat metal with acid metal wash, a solution of Phosphoric Acid and alcohol before painting. This removes waxes and oils, removes slight amounts of rust that form between sand blasting and painting, and leaves a thin protective coat of iron phosphate. One commercial solution for this is DuPont Quick-Prep. Sherwin Williams has a similar product called Metal Prep.”
Denny Graham
Sandwich, IL

Okay, I can't take it anymore...

I'll muddle through this on my own because the information I'm getting from all these different sources is conflicting, confusing, obtuse and contradicts the instructions that comes with the very products I'm being told to use.

No wonder this question gets asked so often... there is no answer. There are hundreds of answers because there are hundreds of products with no standardization using generic terms that have multiple meanings. I'm sorry if my frustration is showing but this is insane.

Thank you to everyone who tried to help... I'm sorry for being so dense. I'm calling Eastwood... and then they'll probably tell me something completely different so I can add yet another method to the mess.

BINGO. When all else fails read and follow the instructions. The manufacturers spend a lot of money to determine the best way to use their product. A lot of folks here, though well meaning, give advise that is incorrect. I've discovered a few times that what I thought was gospel was wrong. I know how "I" would treat pitted metal. I know how I've done it in the past. You may not be using the same products I used and most assuredly you're not treating the same metal I did so the "best" method I know of is to follow the instructions given by the maker of the treatment product you're using.

I agree with Tiny. I figure the manufacturer of the product has done a lot more testing than most people will ever experience.

Czechman,
I feel for you man, not just 1 year ago I was sifting through all this and trying to figure out what to do on my axles and frame. I finally decided to call Eastwoods and use one system from one company. I used their rust converter, and Chassis Black. After wire wheeling my axles I applied the rust converter which looked great. Then I dropped a metal bar on the axle and the rust converter chipped like glass right to the metal! I took a screwdriver and lightly tapped other parts and the stuff chipped off way too easily. I called and had conversations with different people at Eastwoods and one guys said I should not have put the rust converter on bare metal even though it says it on the side of the product can! Anyway, I was very frustrated and depressed, that was a lot of work that had to be redone! I decided to continue to work with Eastwoods because it could have been my fault (maybe I didn't prep well enough or mixed incorrectly) and they were good about giving me a refund. They recommended that I use Epoxy Primer on the bare metal. I am extremely happy with the results. That stuff is tough. I used the Extreme Chassis Black for a top coat. It looks good and it adheres well to the primer, but if you drop a wrench on it, it will chip. But not to the metal just to the epoxy primer. Here is a link to my project: 1955 Chevy 4x4 NAPCO
I have found that it is best to learn by trying, failing and trying again until it works. I'm good at this, believe me!