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Thread: primers for steel tube-- compatable with polyfiber

  1. #1

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    Default primers for steel tube-- compatable with polyfiber

    I am stripping and cleaning -blasting in spots- on steel tubing. getting rid of the old 25 year old gook that wasnt put on well--
    I keep hearing that polyfiber is the least finnickey of the covering systems---- so I's considering that as my default system when I get to that stage.
    In the mean time I want to be priming as I go. After I strip / blast--- i intend to phosphate and then epoxt prime with something----
    I have been using stewarts 2 part water based epoxy on sheet aluminum bearhawk ribs. Like it OK for that--- but I'm not sure I want to shoot water
    base anything over steel tubing---- (rust?) So Im thinking I want to use a traditional 2 part solvent based epoxy. Will any of the common ones
    be compatible with the glue for polyfiber ? I would THINK that any well cured epoxy could be impervious to fabric glues--- but im NOT sure of that----

    I want to start out with a product that I KNOW wont have a bad reaction or lift unexpectedly...… when hit with the fabric glue.....

    I can call stitts---- but concerned they might not recommend other product brands which might be fine chemically.

    Thanks for any experiences related....

  2. #2
    kevbot's Avatar
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    Default Re: primers for steel tube-- compatable with polyfiber

    Sounds like you want Stits EP-420 Primer

  3. #3
    Jim's Avatar
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    Default Re: primers for steel tube-- compatable with polyfiber

    Hi,

    Epoxy paint over the primer, preferably two coats.
    EAA Technical Counselor #4562
    Experimental Aircraft Association #140897 (1977)

  4. #4
    Administrator Steve Pierce's Avatar
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    Default Re: primers for steel tube-- compatable with polyfiber

    I use to use the Poly Fiber epoxy primer but it takes up to a week to cook before it can be top coated or covered over. I started using PPG DPLF 2 part epoxy primer because it can be top coated a few hours later. I have not covered over the top of it because primer is not a sealer and it will evntually show rust. I top coat the epoxy primer with catalyzed polyurethane Aerothane or Randthane. No rust and not effected by PolyTac or other solvents.
    PPG DPLF Epoxy Primer

  5. #5
    Frank Green's Avatar
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    Default Re: primers for steel tube-- compatable with polyfiber

    I use PPG DP48LF and DP402LF activator 2 part white epoxy primer under polyfiber. The STC calls for epoxy primer not necessarily theirs. It is available locally from a auto body supply store. Comes in 2 varieties, mix and shoot with a short pot life (402) or mix and wait with a longer pot life(401). I like the mix and shoot as I mix what I think I need but if I run short no big deal or waste by mixing too much. Toooo expensive to waste.
    -Super Stub-

  6. #6
    Frank Green's Avatar
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    Default Re: primers for steel tube-- compatable with polyfiber

    Steve I think we were typing at the same time but on the same wavelength.
    -Super Stub-

  7. #7
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    Default Re: primers for steel tube-- compatable with polyfiber

    I use Nason Ful-Poxy DTM (Direct To Metal) primer. I can get it locally in quarts or gallons and it is much cheaper than the EP-420. All epoxy primers have a 7 day cure time for full cure, but as Steve said if you topcoat it should be done within about 30 minutes and can be covered in less time. I generally wait the 5-7 days because I have plenty of other stuff to do anyway but moisture will not penetrate the cured epoxy and I have never seen rust trough the epoxy like with the single stage primers. The 491-16 is a primer sealer and is a light gray and does have an induction time of either 30 or 60 minutes depending on temperature. Also available is 491-35 off white and has no induction time.
    Last edited by Wag-builder; 06-13-2019 at 07:39 AM.

  8. #8

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    Default Re: primers for steel tube-- compatable with polyfiber

    I cant see any reason to top coat an epoxy primer if you don't mind whatever color it is--- am I right in thinking it should be just as impervious to environment as an epoxy paint
    which you might overcoat it with ? So- all the topcoat would be doing is changing the color and gloss --- do I have that right ? So I could only use a topcoat maybe in the cockpit where it shows...…
    Tim

  9. #9
    Administrator Steve Pierce's Avatar
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    Default Re: primers for steel tube-- compatable with polyfiber

    Quote Originally Posted by violinmaker View Post
    I cant see any reason to top coat an epoxy primer if you don't mind whatever color it is--- am I right in thinking it should be just as impervious to environment as an epoxy paint
    which you might overcoat it with ? So- all the topcoat would be doing is changing the color and gloss --- do I have that right ? So I could only use a topcoat maybe in the cockpit where it shows...…
    Tim
    Do a little reading on primers and you will find out they are designed as primer for top coat not as a sealer. I have worked on a lot of tube and fabric airplanes over the years and it becomes very obvious which fuselages have primer on them and which have been top coated with polyurethane. There is a reason Aviat, American Champion and Maule do it.

  10. #10
    Gilbert Pierce's Avatar
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    Default Re: primers for steel tube-- compatable with polyfiber

    And AirTractor which get doused with all sorts of chemicals.
    Air Tractor primed and top coated my fuselage 15 years ago. The only rust I have is the engine mount which was powder coated.
    Last edited by Gilbert Pierce; 06-13-2019 at 06:32 PM.

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