Mr Charles

Mr Charles

Well Known Member
I am installing new F-451 cooling tunnels on my 17 year old RV-4, (didn't build it...but have done enough modifications that I feel I could have!:) and have a question regarding alodine...
I etched and alodined the new 451's, but the bottom skin where they attach is going to be etched with alumiprep and either alodined, or primed with a non-self etching epoxy primer.When two parts are riveted together, will the alodine work OK against either another alodined surface, or against the epoxy primer? Or do I need to pre-prime the 451's also before riveting on?

Thanks for any advice...
Mr Charles
 
All 3 steps.

Alumiprep cleans chemically, Alodine etches for primer adhesion, Primer seals it all up. That whole process is what will give you best results. Both Alumiprep and Alodine need to ne rinsed completely, and dried prior to priming. Use of Scotchbrite to mechanically clean is also a good idea if there is any slight corrosion.
 
Your 17 year old RV is never going to care no matter what you do. Just stick it back together and have fun.
 
Mr Charles said:
<snip> When two parts are riveted together, will the alodine work OK against either another alodined surface, or against the epoxy primer? <snip>
Mr Charles
Click to expand...

To your question: Either combination works well. It is probably easier to prime on plane parts and alodine pieces that can be done off plane.

I have become fond of just alodine for small and hidden parts. Quick, easy, no overspray, and no dimensional changes.
 
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one small but important point - Never use a etch primer on a alodined surface .... use a non etch (like a 2 pack epoxy primer) ... If you want to use a etch primer .. then just do the cleaning process .. then apply the etch primer ... if you want to alodine as well ... Well then you do the cleaning process - then alodine .. and you then apply a non etch primer .. some would even say that if you alodine .. and the surface will see no wear .. then just leave it alodined .. as it does offer a excellent barrier against corrosion - only problem with a alodined surface only - is that it is very easy to scratch off ... but for inside the wing or the tail .. rear of the fuselage etc... its great ..
 
Replies were appreciated! Still a few questions.

Thank you all for your replies.
I have been reading the forums for days and also Dan Horton has graciously provided much needed advice along the way! I see why they call it "primer wars":)
In some ways, dealing with repairs/upgrades seems tougher than built from the beginning, at least concerning paint/primer issues. A lot more variables! The original seems to have been all ZC primer, nothing alodined, then a urethane topcoat...and for the most part has held up quite well for 17 years!
I appreciate the reminder about not using a self-etching primer over alodine...I came across that in my forum reading...how about rattle can Zinc Chromate? Is it considered self-etching?
One small thing I am still not clear on...assuming I leave the alodined surfaces of the inside of the 451 tunnels, and the "mating surfaces" alodine only, can I then rivet these to the epoxy coated bottom skin?...i.e. will an alodined surface against an epoxy or Zinc Chromate primer be good corrosion protection between the riveted surfaces?
The last thing I am a little concerned about is using the alumiprep on the belly skin...I will be using it "overhead" and the plane is not in a position to rinse with a hose. So worried about rinsing/flushing prep from spaces/cracks/crevices etc. Maybe I should just scotchbrite with alcohol or MEK and then epoxy primer?

Mr Charles
 
to answer your question on rattle can Zinc Chromate you need to see the safety data sheet ... Zinc Chromate on its own is not an etch ... it has to have a acid component.

If you are not able to wash with the plenty of water - then I would cleaned with scotch brite and alcohol - maybe a final wipe with MEK ... and used a epoxy primer (or a proper 2 pack etch primer) - if using a epoxy primer .. go for a "non build" version ... i.e. some have a filler component to take out irregularities.... which does nothing for corrosion prevention

I would not have an issue riveting a alodined surface against a etch primed or epoxy surface ... If you want to make it even more complicated ... you could use a chromate joining compound !
 
prep

Jan, thank you!
I think the scotchbrite/alcohol followed by MEK wipe is the best choice in my case...
I'm not an expert on any of this, but it seems to me that scotchbrite should remove the surface oxidation layer of the aluminum...serving the same purpose of the acid etch. Of course, it begins to reform immediately, but would also with acid etch! So I will follow immediately with the epoxy primer. And yes, it's a non-sanding epoxy. My understanding is that when I am all assembled and ready for the next step, I will need to scuff the exposed epoxy coat, then re-shoot another coat, followed immediately by a high fill primer (if needed for sanding/filling), or topcoat within the time window (I think it was 5-7 days for my epoxy).
In my case, although I want some corrosion protection, I am mostly concerned with adhesion of primer and topcoat! I HATE peeling paint!!!:D

Thanks again to everyone...will post some pics when finished
Mr Charles
 
Self etch primer and alodine surface

Jan,
I just painted my new smoke oil tank, which I cleaned with Alumiprep, treated with Alodine 1201, then (gulp!) primed with self etching primer. What bad things can I expect to happen? Thanks!
 
Self etch primer over alodine

Has anyone out there had a bad experience with using self-etching primer over an alodined surface?
 
Self Etching Primer

Gil,

Thank you for this specific input. I have been using Mar-Hyde single stage self etching primer. It is not specifically approved as noted in your message. Do you think that a problem could result? Meantime I will discontinue the use of the Mar-Hyde.
 
gear1 said:
Gil,

Thank you for this specific input. I have been using Mar-Hyde single stage self etching primer. It is not specifically approved as noted in your message. Do you think that a problem could result? Meantime I will discontinue the use of the Mar-Hyde.
Click to expand...

The Mar-Hyde (3M) documentation does not say either way on underlying conversion coats.

I suggest contacting Mar-Hyde and asking them specifically.
 
Self etching primer

Thanks, Gil, I will contact Mar-Hyde directly

(edit): Contacted 3-M technical support in Atlanta (3-M owns Bondo, which in turn owns Mar-Hyde). They have not tested Mar-Hyde Self Etching Primer on Alodine treated aluminum. Therefore, no recommendation was made.
 
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Etch ingredients

gear1 said:
Thanks, Gil, I will contact Mar-Hyde directly

(edit): Contacted 3-M technical support in Atlanta (3-M owns Bondo, which in turn owns Mar-Hyde). They have not tested Mar-Hyde Self Etching Primer on Alodine treated aluminum. Therefore, no recommendation was made.
Click to expand...

Out of interest, can a VAF chemist reader say which part of the Mar-Hyde ingredients do the "self-etching" bit?

http://multimedia.3m.com/mws/mediawebserver?mwsId=SSSSSuUn_zu8l00xM8tGnxmBNv70k17zHvu9lxtD7SSSSSS--
 
Chemical etching

Tricresyl phosphate is the ingredient in that formulary capable of chemical etching aluminum.
 
gear1 said:
Has anyone out there had a bad experience with using self-etching primer over an alodined surface?
Click to expand...

Not personal experience but was told in no uncertain terms by an industrial painter that Alodine (chem film) and Wash (self-etching) primer weren't a good combo for long term adhesion. Makes sense if you think about it. You can't etch twice, etc.

I've used Dupont Veriprime a lot and it comes right off with lacquer thinner so depending on what stage you are in recovery should be easy to achieve.
 
rbibb said:
Not personal experience but was told in no uncertain terms by an industrial painter that Alodine (chem film) and Wash (self-etching) primer weren't a good combo for long term adhesion. Makes sense if you think about it. You can't etch twice, etc.

I've used Dupont Veriprime a lot and it comes right off with lacquer thinner so depending on what stage you are in recovery should be easy to achieve.
Click to expand...

Variprime is not a wash primer, which are the types of etching primer not recommended over alodine (conversion coating) surfaces.

This is DuPont's equivalent wash primer product which replaces the alodine step -

http://pc.dupont.com/dpc/en/US/html...avi/Aviation/TDS_13238S_Aviation_Finishes.pdf

However, interestingly enough, Variprime is now not on the list for DuPont aviation painting systems. It seems better epoxy based primers have taken over.

http://pc.dupont.com/dpc/en/US/html...ion_Finishes_System_Recommendations_Props.pdf

But etch and alodine is still on the list.
 
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