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MG Midget and Sprite Technical - bare metal Prep

Gentlemen: A friend of mine who has just painted a TR6 has offered to epoxy prime my fenders and doors for me but I have to act fast. The parts are bare metal, but have not been blasted, just stripped and sanded and stored inside and dry. There is no rust on them in the traditional sense of the word, but as the picture shows, they are not shiny bright and there are small spots of black throughout. Will the application of a metal conditioner be sufficient to prepare these parts for primer or do I have to resand them back to shiny? I don't want to cut corners, but don't want to spend hours doing something that's not necessary-- I'm not getting any younger.

John Campbell

Personally.... The photo looks great to me

I would strongly suggest you contact the guy doing the epoxy priming and see what is acceptable to him or what still needs to be done.... At the end of the day, its his opinion that matters the most

Prop
Prop and the Blackhole Midget

Thanks Prop, My only concern is that my friend is a relative novice and has only worked on cars that have been blasted and then primed almost immediatly. So when I asked him he really couldn't say with certainty.

John
John Campbell

John,

Here is a link that may help.

http://autobodystore.com/forum/showthread.php?18767-metal-cleaner-and-metal-conditioner

Regards,

Larry C.
Larry C '69 Midget

I would treat it first with a metal wash - a phosphoric acid based wash which will remove any rusting that will have started in the micro-pores of the metal surface. I would then immediately treat it with and acid etch primer before the epoxy primer, unless the epoxy specifically has etching/ bonding properties.
Guy W

Oh gez,

Your friends friend thats doing the work has very little experiance ....

Hmmm.... Im not sure what to say, can you read my mind...that pretty much says it all

Prop
Prop and the Blackhole Midget

Hey John,
Where in Canada you located?

My advice: close your eyes and feel the metal with your fingers. If you can feel any discrepancy between the "shiny" metal and the "black spots" you'll see it when painted.

So it comes down to you regardless of your buddy's skills. Do you want to see any "imperfections" or are you happy if it looks good from 10' away (or to a man on a galloping horse)?

If you want perfection...take it down to shiny metal. Body prep for painting is 99% of the process.

Chris
Chris Elkerton

Hi Chris, I'm in Victoria, BC. I've been thinking about this a lot and even before I read your post I decided not to rush into this and make sure it's done right. If I miss this chance to get the parts primed, there will be another time. This afternoon I started in on a fender using a scotchbright disk, and it shines things up quite nicely although it leaves fine scratches in the metal. I assume these are no problem, as the epoxy primer should cover them. My main concern is oxidation and poor adhesion.

John
John Campbell

A rinse over with an acid based metal cleaner would probably have the same effect as the scotchbrite, only would be more effective at getting into the microscopic cavities and depressions in the metal surface. It should be used anyway before spraying unless you have use of a drying oven as otherwise any dampness in the atmosphere will initiate microscopic rusting of the unoxidised surface within minutes.
Guy W

John, I will shortly be in the same situation as you when I bare metal my MGB and want to ensure that it is bare metal for the minimum amount to time. So I would remove as much of the black spots as possible, treat with a metal wash as Guy says and then etch prime and epoxy prime. I would worry about any surface imperfections until later. This is of course dependent on whether it is ok to put filler on top of epoxy primer or whether it should go direct to metal.
Steve Church

OK, Does one need to apply a degreaser as well? My guess is thatthe application of the metal cleaner doesn't provide any protection from rust, so the metal should be primed as soon as possible after washing. Have you heard of epoxy primers that contain zinc chromate that can be applied to the metal without the need to etch prime? One last question, does the metal need to be scratched up a bit with something like 120 grit to get better adhesion?
John Campbell

painting is such a can of worms. . .its very easy to be drawn into the search for perfection or even the best you can get. . .however the importance for me really is the balance all the way through the car. What i mean is, if the rear wings look fab, then it will highlight the rest of the car unless its of a same standard . . .very very few cars that get used will stay looking amazing due to stonechips, wear and tear, car park dings etc, as well as the the dreaded tin worm taking hold.

I chase perfection in my own paintwork, but have never acheived it ! but i guess its a question of what you can be happy with. . . i love the galloping horse analagy. . . its so right
p bentley

Hydrochloric acid will eat off the black spots, which are rust.
Phosphoric acid will stabilize bare steel by forming an insoluble iron phosphate layer, good to paint.
Art Pearse

Phosphoric acid with zinc (Oxisolve or similar) in produces a zinc-iron phosphate coating. It does the same thing as acid etch primer only better, and the zinc gives some of the same advantages as galvanizing - a sacrificial zinc coating. The remaining coating is crystalline in nature and provides the best possible base for primer.

It should all have been degreased long before this stage, but keep your fingers off the clean metal.

Oxisolv, epoxy primer, sand/fill primer-surfacer, paint.

Better still is Masterseries MCU primer instead of the epoxy - MasterseriesCT.com - everything it says on the site is true and Chuck is a good guy for real, and an experienced restorer. I use it on everything.

FRM
FR Millmore

This thread was discussed between 26/09/2012 and 04/10/2012

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