Metal protection during restoration?

[nathandarby67]

I have a 73 Midget on which I am getting ready to cut out some rusty areas, mostly in the inner fenders, as well as replace the floor pans. Due to my schedule, I likely won't be able to do the job all at once over a weekend or something, but rather work on it a couple of hours at night over several weeks. I will also soon be stripping paint to prepare for a repaint. So my question is this: when doing body work that exposes bare metal, how do you prevent corrosion from starting on the bare metal you have finished working with while you are working on other parts of the car? (The car is in a non-climate controlled garage.) I have seen several brands of spray on stuff that is supposed to do the trick, and other people have told me to just spray a light coat of primer. I would just like to hear what has worked for other people out there, or is this type of protection really even necessary? I have heard tales of dreaded "flash rust", but what's the real scoop?
/ubbthreads/images/graemlins/confused.gif

 

[Nunyas]

I've always just laid on a layer of primer to protect the bare metal from rust... The last time I did any body work was quite a while a go, and I was living in FL at the time. I just used rattle can primer at the time and it seemed to do the trick. I'm not sure if there's any primers better than any others; hopefully someone will show up with better knowledge in the what primers are ideal department... /ubbthreads/images/graemlins/smile.gif

 

[dklawson]

During my last project I did exactly what you're describing. I limited my nightly projects to no more than one panel at a time. I preped the stripped panel with a phosphoric acid wash. Once that process was done, I dried the panel and applied my etch primer and a coat of the high-build primer. Friends of mine who do this more often than I said a better choice would have been epoxy primer. They're probably right. It would have been one less thing/coat to spray and supposedly it seals the surface better.

This may sound unimportant, but choose your top coat paint system now before you buy any primer. Even though you won't be buying your top coat paint until you're done with preping the body, choose a primer that is compatible with your color coat and only use it. Try not to use hardware store primer under that expensive top coat you'll be applying.

 

[Scott_Hower]

Depends on how serious you want to prep the surface. If you only want to prevent flash rust, which is INEVITABLE, Rustoleum/Krylon is fine for a few weeks/months. Primer is hygroscopic - it soaks up water - so it will not prevent further rust for very long. If you want more serious protection, single stage self-etching primer is a better bet (rattle can at a paint jobber or Eastwood.com). In either case, I'd strip it off when you get ready for final prep and lay down a really good quality 2 part etching primer, followed by a high build sandable epoxy primer.

 

[John Moore]

I've had my car pulled apart for a few weeks now. Some of the metal I've stipped. I've had not ill effects what so ever.

 

[dklawson]

John, having lived in Albany for a while myself, I wouldn't expect the humidity this time of year in upstate NY to cause you any problems. However, below the Mason-Dixon line the humidity begins to rise as early as February and surface rust can become annoyingly developed even after just one night.

If you plan on only leaving a panel un-painted for a couple of days, proper treatment with phosphoric acid will be sufficient. Anything longer really needs a coat of good primer. BTW, since I haven't used epoxy primers my next comment is strictly hearsay. However, I've been told that epoxy primers are significantly less hygroscopic and provide much better protection than my etch primer covered with high-build. Keep in mind that good primers will cost good money.

 

[John Moore]

Doug, you're right! It's not particularly humid... yet!

 

[hottvr]

Etching primer works the best for me. I've covered stripped areas with it and left it for a month with no rust appearing. You can't buy it at an auto parts store. You have to get it from an auto paint supply store and it costs $12-14.
Rick
85 TVR 280i
78 MGB

 

[RichC]

On another note ... I've noticed some 'black' primer (don't recall the name) that is in a spray rattle can that is suppose to be used to spray on the prepped area that might still have those little pits of rust ... the primer/spray is suppose to 'eat' the rust like a derusting acid and 'convert' it to primed surface paint. (which I believe is black) I'll have to look at the name again .... or am hoping someone has knowledge about it.

My thought (haven't tried it yet) was to prep the surface bare, spray this primer/rust eater on to protect and eliminate the tiny rust pits then sand, prime and body work as usual? Any thoughts?

 

[dklawson]

Rich, don't take this wrong, but DON'T use conversion coating primers. Duro used to sell a type of primer like this under the name "Extend". These primers don't do a good job at converting the rust before they dry. I used the stuff and found myself re-stripping and re-painting a part two years later.

The phosphoric acid treatments I mentioned require you to keep the panel wet with the acid for at least an hour (it must not dry on the panel... keep it wet until you rinse and dry the panel). It isn't quick but it makes all the difference in the world at eating small bits of rust and leaving a phosphate coating behind. The phosphate coating is a surface that is excellent for primer adhesion. The acid is available from multiple sources. Eastwood sells it (until recently they sold OxiSolve, now I think they have their own brand), POR-15 sells it as "Metal Ready", and the old standby is Ospho (and clones of it). These work much better than the conversion coatings or products like Naval Jelly.

 

[Nunyas]

eh... I've not had very good experience with Naval Jelly either. I had a rusty spot that I cleaned up and coated with Naval Jelly when I lived in FL, only to have rust bubbles appear under the paint in the 'protected' area within a year. Maybe I did it wrong, but i was still disapointed none the less.

 

[RichC]

Excellent ... exactly what I needed to hear 'dkl.' I didn't purchase the primer/rust converter product but was reading some product labels. Sounded too good to be true but I've been surprised with improvements in chemistry before. /ubbthreads/images/graemlins/square.gif

I do have the acid and wash product that I've been using but have always been concerned about making sure I've washed it off. Thanks for the advice.

 

[r67cat]

Doug is absolutely correct in his earlier response, that you should choose your top coat now and use only the compatible primers, high build primers and sealants that are recommended by that manufacturer. I have seen too many paint jobs fail due to incompatible, or less than ideal products. PPG, 3M and any many other companies provide an engineered system of coatings. In my opinion Epoxy primer is the first step. Applied to properly prepared bare metal, body filler or OEM coatings it will provide protection while further body work is completed it is not hydroscopic. PPG recommends that all body filler be applied over their epoxy primer. Properly applied epoxy primer provides the best base for all further work. Follow by high build primer, block sand, seal coat, color coat and clear. Has always worked for me reguardless of how long the project took. Rick

 

[dklawson]

I saw my Triumph buddy last night. His TR6 has been in pieces for a decade and he's just now getting back to it. The body tub has been coated in epoxy primer for that entire period. The only issues he's seen with the primer over a DECADE of being the only coating on the car... is low adhesion to the "brazes" a previous owner made during repairs. The epoxy has protected all the steel on the car for over ten years without rust.

The next project I take on will get the epoxy primer instead of the etch primer. I have used PPG products most recently, but I've also used Martin-Senour (NAPA) and DuPont paints. All are quality but I liked the PPG best. Choose a good quality paint and you won't be sorry... except when you're paying for it.

 

[Scott_Hower]

[ QUOTE ]
Properly applied epoxy primer provides the best base for all further work. Follow by high build primer, block sand, seal coat, color coat and clear. Has always worked for me reguardless of how long the project took. Rick

[/ QUOTE ]

Agree that epoxy is the best base for topcoat, but etching primer provides the best surface adhesion and protection for the initial substrate. It chemically bonds to the surface.

Everyone has their favorites, but IMO the best system on the market is Glasurit.

 

[beaglbut]

I also agree about both the epoxy primer and the selection of a paint system before you start. You can cover the epoxy with a high build primer/surfacer later. I've used PPG/Omni with good results in the past.
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70 MGB/GT
67 A/H 3000 BJ8
95 VOLVO 850 TURBO WAGON