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Primer Moisture Absorption

Discussion in 'The Hokey Ass Message Board' started by 36 ROKIT, Aug 21, 2010.

  1. A couple of recent threads on this subject got me to thinking more about the possibility of hidden gremlins under the 45+ year primer (Rustoleum, as I recall) on my coupe. I have a spare fender that I am subjecting to my body and paint "skills", so decided to strip it back to the bare metal. Sure enough, my worst fears were realized.

    How does this happen in a dry storage environment? We have humidity here in the northwest to be sure, but its not as if the car has been directly exposed to it over the years. Looks as though I will be starting from scratch on the body, as well!!

    Attached Files:

    Last edited: Aug 22, 2010
  2. So, how about it, paint experts; is an etching primer or epoxy the better way to go if my final paint job is still a couple of years away? (I have an OMNI epoxy primer on tap to use as a new base after sanding out the remainder of the surface rust.)
  3. carcrazyjohn
    Joined: Apr 16, 2008
    Posts: 4,844

    from trevose pa

    It all sums it up to ,Neil Youngs famous album and lyric to a song ,Rust never sleeps . You can kill the fungus but it always returns ........
  4. Water is known as the universal solvent. Given enough time it will penetrate MANY surfaces. Due to the chemical nature of primer (not to mention the formulation of decades-old primer) the penetration will happen quickly. Primer is designed to have a top coat, so it will allow penetration.

    Shit happens. Just suck it up and re-finish.

  5. jerry325w
    Joined: Nov 10, 2005
    Posts: 93

    from baltimore

    epoxy primers may be best, less pores in the surface for moisture to pentrate, see lots a primer cars nowadays and most paint manufacturers will tell you declining resistance to moisture after 90 days at most.:(
  6. i used some Rust Control spray bomb stuff on Lil Beast...after i used chemicals to clean every pitted, rusted section of my topolino...thats been well over a year ago..had to clean it off to weld in the roof to wondering if it had rusted under the paint..cleared off the area i needed clean to weld with thinner,,,no rust...supposed to have a 3 year warranty against rust if de-rusted the end i plan on having my body dipped...some day...

    primered a cj5 years ago, with standard good mix primer..the good stuff...after a winter inside i went to do some work on it and it was rusted under the primer..everywhere....
    hey hey, my my..rust will never die...........

    but can be checked to an extent.........
  7. Droppedhatch
    Joined: Jun 17, 2010
    Posts: 37


    It all depends if the primer that you are using has any sealing qualities. A lot of the spray bomb have zero sealing qualities. You have to make sure that it works as a sealer, if it does not the primer is porous and the moisture will wick right though it. Take to the guys at your local paint store and they can get you on the right track.
  8. pimpin paint
    Joined: May 31, 2005
    Posts: 4,937

    pimpin paint
    from so cal


    There's the possibility that the rust was in the grains of the metal prior to your primering it twenty? years ago. Once the binder, that's the oil in the Rustoleum breaks down from the attack from oxygen, rust + moisture+ oxygen = more rust. It doesn't take much moisture to get it started.

    Today, I wouldn't waste my time with epoxy primers given they no longer contain lead, zinc or cadminim. Instead, step up to a full urethane primer with better resin technology. And remember, anything that comes in a rattle can was designed for use by your wife for her craft projects, NOT for use on motor vehiciles.

    " Everything is rotten with time "
  9. not to start a pee :eek: pee contest here, but........after a year, the spray can stuff i used has zero rust under it...and i also plan on having my body dipped and done professionally before it gets it ain't like we don't have any humidity here in michigan....i was looking for something to apply as i went about removing what lil surface rust i had...maybe the chemical rust removers and all the brass wire wheeling i did helped...

    my goal was/is to maintain a damn near rust free cherry 72 year old topolino body....i spent over 3 months cleaning pits.....and am happy with where it is today....:D
  10. Rich Wright
    Joined: Jan 9, 2008
    Posts: 3,922

    Rich Wright

    Rust NEVER goes away. If there is any corrosion present on the metal, even under a lap or overlap seam, it will eventually creep out and cause a failure of the coating used to cover the metal.

    All primer, even catalyzed epoxy primer, will absorb moisture and eventually a failure attributable to rust/corrosion will occur.

    It's all a matter of degrees.... Depending on the exposure to moisture or the degree of existing corrosion, it may take weeks or years for it to make it's presence know. Rest assured, though, that it will eventually show up.

    Even if the car body was carefully media blasted and then etch primed, which will pretty much eliminate further corrosion, rust can still creep under the etch primer if it was hidden under a seem somewhere.

    The chemicals on the market that are designed to prevent corrosion only work if there is NO corrosion to begin with.

    The chemicals on the market that are designed to neutralize rust only work on the rust it reaches.

    These two "rules" are exacerbated by the lack of a top coat.

    All of this is why I have such a hard time understanding the whole bare metal/primered car thing...... The amount of work required to reverse or repair the damage caused by leaving the metal exposed is monumental and often enough to destroy the value of the car.
  11. Many thanks for the replies. Another good edjication.

    Looks as though I will be heading back to the paint store for a lot more sandpaper; but, better safe than sorry. Want to be sure this cherry old body has a sound base..
  12. Antny
    Joined: Aug 19, 2009
    Posts: 1,071

    from Noo Yawk

    My truck is in primer (PPG DP701LF, red oxide), about 7 coats of it. It sees limited use (weekend use in nice weather only). I didn't top coat it with nice paint because I know for a FACT that it'll get scratched and chipped up (I live on a gravel road, and in a community of many unpaved roads), which makes a shiney paint job look crappy, imo. BTDT. So I want to leave it in low-maintenance/easily touched up primer. LOL. Question: does it make any sense to put a wax, or some other protective application (besides paint, lol) onto the primer to help it repel water/retard the UV issues? Just asking, not looking to start any sort of pissing contest, I'd definitely lose! :)
  13. customcory
    Joined: Apr 25, 2007
    Posts: 1,832


    Where I live the humidity is usually pretty bad, so when I sand blast a part I will DP-90 it within a hour of getting done. If I strip some sheetmetal down , after it gets 180 grit sanded , it gets primered and I adjust my schedule too do it. Its the most important thing. I've seen sandblasted metal start rusting again by the end of a workday left unattended. That rust starts microscopically in the pores of the metal, so its the rust you don't see that gets you.
  14. langy
    Joined: Apr 27, 2006
    Posts: 5,735

    Member Emeritus

    Epoxy primer is the way to go, its non pourous and anti corrosive, i started using it 20 years ago and have never regretted it.
  15. overspray
    Joined: Jan 14, 2003
    Posts: 1,232


    OK--everybody read this 100 times--- then read it again
  16. ogorir
    Joined: Aug 20, 2010
    Posts: 21

    from Waco, TX

    most rust issues I've seen come back are places where rust wasn't completely removed. (I work for my dad restoring cars, he has been using PPG DP50 >K36> DBC>2020(until they discontinued it) for over 20 years) we recently worked on a car we did 15 years ago (got rear-ended) and there was no surface rust under the paintwork.

    I haven't done this personally, but this would be my approach for a primer finish: metal prep> DP>k36>3 coats 8150 clearcoat> DP again.

    the clear will give you as good a moisture barrier as you're ever going to get between the elements and the steel.

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