Alodine competed components

[Dean Pichon]

Originally Posted by Loman

A fellow chapter member, who is a college engineering professor, is adamant that Alodine (Bonderite) is a strong acid that will continue to erode within the joints when applied to finished assemblies. He says it is only designed for individual parts and that, if used on finished assemblies, it will penetrate joints to the extent that it cannot be fully rinsed out. That?s apart from the nastiness of the stuff itself.

Does this argument have any credibility?

I just looked at the MSDS for Henkel Alodine 1201. It lists the pH as <2, so it is a very strong acid. I had always wondered about using Alumi Prep 33 (Phosphoric acid) on assemblies, but never realized that the conversion coating is acidic, too. Completely rinsing it from a completed aircraft would seem difficult, but many planes have been repainted this way. I've never heard of residual chromate damaging the structure, but it does beg the question.

[rv7charlie]

My understanding, as someone with no recent hotel stays, is that 'conversion coating' means, in lay-bubba terms, 'a special kind of corrosion that creates a layer that prevents further regular corrosion'.

Like what happens in an imperfect way with pure aluminum, but is compromised by the alloying that makes 2024 so strong.

Charlie

(Bubba from Slobovia)

[fl-mike]

he is wrong.

[snopercod]

Originally Posted by Mike H

Prior to applying alodine the surface of the aluminum must be made water break free.

On the Space Shuttle they sanded with 320 grit wet/dry to get a "water break". Then etched with phosporic acid. Then flushed with copious amounts of water, then tested with Litmus paper strips to make sure no acid remained. Then Alodyne. I've used cotton balls to rub in the Alodyne for a nice, even straw color.

[lr172]

Originally Posted by Loman

A fellow chapter member, who is a college engineering professor, is adamant that Alodine (Bonderite) is a strong acid that will continue to erode within the joints when applied to finished assemblies. He says it is only designed for individual parts and that, if used on finished assemblies, it will penetrate joints to the extent that it cannot be fully rinsed out. That’s apart from the nastiness of the stuff itself.

His argument sounds persuasive, especially when you see the TDS advises avoiding all metal containers. Yet I read here that this is SOP for aircraft painters. I see Homebuilt Help also has a Youtube on the procedure

I really want to use this method, having lately chickened out of wrapping over bare metal here in my maritime environment.

Does this argument have any credibility?

The acid keeps corroding/converting until neutralized with water. If the alodine finds it's way to a joint and the rinse is not thorough enough to get it out, it will continue to corrode/convert. This is a risk when alodining a finished plane. One must be cautious and thorough to insure no alodine remains after the rinse.

Once neutralized, there is no acid left to corrode, whether on a surface or in a joint. The converted material is not acidic and does not continue to corrode. It doesn't matter if the paint blocks the air or air is blocked due to a tight joint. The key is a complete neutralization.

And, yes, the surface must be free of any oxidation before alodine application. The oxidation layer forms in a few hours, so the surface must be etched, chemically or mechanically. The alodine will eventually eat through the oxidation, but not within the time specified in the instructions. Standardized dwell times are based upon a clean surface, with no oxidation.

Larry

[wirejock]

Originally Posted by Loman

A fellow chapter member, who is a college engineering professor, is adamant that Alodine (Bonderite) is a strong acid that will continue to erode within the joints when applied to finished assemblies. He says it is only designed for individual parts and that, if used on finished assemblies, it will penetrate joints to the extent that it cannot be fully rinsed out. That’s apart from the nastiness of the stuff itself.

His argument sounds persuasive, especially when you see the TDS advises avoiding all metal containers. Yet I read here that this is SOP for aircraft painters. I see Homebuilt Help also has a Youtube on the procedure

I really want to use this method, having lately chickened out of wrapping over bare metal here in my maritime environment.

Does this argument have any credibility?

Larry is correct.
Feel free to PM. I learned a lot on the project and happy with the results. Feeling much better about vinyl.

[Loman]

So, here's what I have picked up and some of my remaining questions:

• Alodine is a good strategy under vinyl. It reduces the chances of corrosion beneath the film, retains the weight advantage, provides a good key for adhesion and won't partially rip off when the vinyl is being re-done in the future. It is also a whole lot cheaper than priming.
• Alodine won't work unless the surface if very clean, with little or no oxidisation. This probably means treating suitably sized surface areas and going straight through all of the chosen process on each area before proceeding to the next. It seems about 1-2 sq yd at a time might be a practical maximum to prevent drying of either Alimiprep or Alodine before rinsing. Is that a reasonable approach?
• Both Alumiprep and Alodine are corrosive and need to be fully neutralised with water. The problem here may be the joints. How about power washing after a low-pressure hose rinse?
• This stuff is very nasty (ask Erin Brokovich!) so you have to protect yourself from ingestion and even skin contact. I don't think just rubber gloves will cut it. What other/additional protective garments have people used?. Fumes on the other hand, do not seem to be a problem.
• You can't let Alodine into the environment. You have to collect the rinse water. It can be left to reduce down through evaporation but then must be disposed of safely. One strategy picked up elsewhere is to mix the reduced run-off into concrete. I certainly have a lot of projects around the garden that need concrete. The question is how much run-off is likely to be generated. If it runs into hundreds of gallons then that is way beyond what a normal person could process.

[RVDan]

Not to debate the effectiveness of either, but why not use Precote. No toxic waste disposal issue, and has been accepted by the military in some circles as alodine alternative. Sound to me like something what might serve your needs well

[cczarnik]

Originally Posted by RVDan

Not to debate the effectiveness of either, but why not use Precote. No toxic waste disposal issue, and has been accepted by the military in some circles as alodine alternative. Sound to me like something what might serve your needs well

IIRC Prekote is a bonding agent and has no inherent corrosion protection. The anti-corrosion performance is enhanced by the bond improvement of the subsequent coating. For a wrap I don?t know how that would work.

[rv7charlie]

But effectiveness will be debated, of course. Quick search yielded this:
https://cen.acs.org/articles/95/i9/C...omium-ban.html

I guess the question is whether III is 'good enough', or do we really need VI.

BTW, the correct name seems to be 'PreCoat'; 'Precote' seems to be a thread locker.

Charlie