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Rust prevention

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RyanBez

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Alright, I know I saw someone talking about this before, but I couldn't find it by doing a search. I am most likely going to have my Sprite professionally painted. However, I want to do the body work myself.

What can I do to sand the car down, but prevent rust from appearing between the time I sand and the time it gets primed/painted? Is there anything good for temporary prevention? Obviously I wont have the whole car sanded in a day, so what are my options?
 
Phosphoric acid is all you need. It will dissolve rust as long as it kept wet by repeated applications. It converts the rust to ferric phosphate (black or dark gray coating), which will protect the metal for a lengthy period of time. When you are ready to do body work and prime the metal, you can scrub or wash it off to reveal a fresh metal surface. Some people say you can leave the coating, but the paint won't bond to it as well, so it's best to clean it off when you are ready to proceed with paint.

You can find it by the gallon is home improvement stores as "Metal Prep and Prime". I like the Kleen-Strip version, about $15 a gallon. You can pay 3 to 4 times as much buying other "metal conditioners", but it won't get you anything better.
 
If you use the phosphoric acid method make sure to clean it off the surface before applying your primer coat. The primer and paint might stick to it for a while, but my experience has been the adhesion won't be as good as a clean metal surface.
 
Awesome, thanks for the advice. I have to take a trip to Home Depot anyway!
 
jhorton3 said:
If you use the phosphoric acid method make sure to clean it off the surface before applying your primer coat. The primer and paint might stick to it for a while, but my experience has been the adhesion won't be as good as a clean metal surface.
Click to expand...

Thanks for reiterating that. I had a guy on MGE get into a big dispute with me me over that fact. He had no personal experience with it, but he had "asked around", so that "research" made him an expert over my 40 years of actually restoring cars.
 
I've learned it luckily not on body panels but on parts. Thought the same thing that I could just scuff it a little, primer and paint, and sure enough the paint and primer would flake down to bare metal after a while.
 
Well, I only have 20 years experience. I never paint directly on the phosphate coating as left for months. If the surface has been sitting I wipe the surface down with fresh phosphoric acid, rub a bit with a brush or cloth, then rinse and blow dry. The etched surface left behind and any thin phosphate coating is fine under paint. What you are trying to avoid are thick buildups, particularly the "white" coating left if you allow the phosphoric acid to dry on the surface. I guess that puts me in the middle of the leave-it/remove-it argument.
 
dklawson said:
If the surface has been sitting I wipe the surface down with fresh phosphoric acid, rub a bit with a brush or cloth, then rinse and blow dry.
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Doug,

This IS the correct way to do it. Refreshing the application will removed any coating/residue from a previous application, and gives you a fresh "tooth" for the paint adhesion. When not using metal conditioner, any surface, be it paint or bare metal, that has been prepped more than a few days in advance of painting should be scuffed either with red Scotchbrite or 320 sandpaper a short time prior to painting to get the best result.

I also never paint either bare metal or primed/pained surfaces without a thorough cleaning with degreaser. You may think that bright piece of metal you just hit with a wire wheel or sandpaper is clean, but take a white paper towel and some degreaser to it and you'll me amazed what you'll find on the towel. It usually takes 3 to 4 thorough wipe downs to have a clean surface.
 
Gerard, do you have a particular recommendation for a degreasing product you like?
 
If I can't prime or phosphate treat them right away I keep my newly stripped parts covered in clean sheets with blankets over them.
 
Yes, but I might be more limited here in California than you would be. The product I used to use has been outlawed. I have always bought whatever the professional automotive paint supplier carries. I'm not sure what the difference is, but the stuff I buy is now labeled "Bug and Tar Remover" That labeling may be some "workaround" to satisfy some EPA requirements, but I don't think it's the same stuff you get in the auto parts stores. There are two brands I've purchased lately, depending on what's available. It seems to change every time I go in to get supplies.

Currently I'm using DuPont 139 Bug and Tar Remover... I can't recall the previous brand, but pretty much the same thing.
 
bug_sixty said:
What about acetone? doesn't have cleaning properies with no residue?
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I suppose that's fine but it's very volatile, way more nasty to work with and not paint friendly. I suppose it's OK on bare metal, but wouldn't chance it on any painted surface. It probably dries too fast to be the best way to do it anyway.
 
I'll be painting my now bare metal engine bay and firewall once I get some decent weather and time.

A couple areas are a little problematic- the base of the battery/heat plenum, and the inner front fender wells are pretty pitted with some rust probably still at the base of the pits. The rest is pretty much shiny steel.

I plan to prime with epoxy primer when I can.

Meanwhile, I have two products in hand:

Rustoleum "Rust reformer"
and
Eastwood's "Metal prep and Prime" (which I assume is pricy phosphoric acid).

Should I use one or both products?

tia
Fred
 
I would put the epoxy primer on now before things start rusting.
 
TulsaFred said:
I'll be painting my now bare metal engine bay and firewall once I get some decent weather and time.

A couple areas are a little problematic- the base of the battery/heat plenum, and the inner front fender wells are pretty pitted with some rust probably still at the base of the pits. The rest is pretty much shiny steel.

I plan to prime with epoxy primer when I can.

Meanwhile, I have two products in hand:

Rustoleum "Rust reformer"
and
Eastwood's "Metal prep and Prime" (which I assume is pricy phosphoric acid).

Should I use one or both products?

tia
Fred
Click to expand...

Fred

They are likely both just phosphoric acid with perhaps some additional additive, stabilizer, extender, etc. If it were me (keep in mind I have an obsession with getting rid of all remnants of rust), I would continue dousing the pitted areas until all the rust is dissolved. That's just me.

What all these products do is convert what's in the surface to an inert coating (ferric phosphate), but it's pretty much just superficial encapsulation. If you scraped at it, you'll find there is still iron oxide underneath, if it hasn't been dissolved completely. It's better than just painting over iron oxide.

If you can keep oxygen and water from making contact, you'll slow the deterioration, but there is still rust underneath. Paint is still porous, especially primer, so there is alway the possibility of it becoming active again. It's possible through repeated applications and abrasion to dissolve it all. The ferric phosphate, especially when it's thick, can easily be scraped off like paint.
 
Well you guys have covered the outside pretty well. How about where the gremlins get started, the inside! I drilled a hole on the inside of the A post's and pumped in some waxoyl. Also some over the rear wheel wells and behind the rear wheels and into the front of the rockers. Is there a better way to protect these areas??

Kurt.
 
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