Hybrid Alodine/self-etching primer a workable solution?

[ibgarrett]

This was on my list to also ask about (and maybe should be in a different thread), but in watching a lot of the alodining videos it seems pretty straight forward of 3 different baths to dip the material into. I was thinking I would like to do all the small parts in the Alodine and then treat the joining surface with the Self-etching primer on the non-alodine treated joints. Effectively we would have one component treated with alodine and the other component with the self-etching primer meeting up. I know dissimilar metals/materials sometime can be an issue, but would this be an issue doing it this way? I just don't want to do the alodining on the big parts.

Anyone have any thoughts on this process?

 

[Bell206]

Anyone have any thoughts on this process?

FYI: A lot depends on the exact materials you are treating, whether you intend to prime and paint them, and environment the parts will be exposed to. Keep in mind Alodine can serve 2 purposes in preventing corrosion and providing a base for your paint to adhere to. So if going to paint these areas may want to check out what your paint OEM recommends for prepping the area. Dissimilar metals and certain faying surfaces will usually require additional measures other than just Alodine or primer.

 

[Huckster79]

I like epoxy primer a lot- A LOT - better than self etch myself... that could be applied to both surfaces, it just seems like a lot tougher stuff, sticks permanently to ANYTHING and has a lot better adhesion for the top coat(s).

I did my plane interior w self etch, I have spots that are chipping. I switched to epoxy and everything I’ve done since turns out very nice and no chipping...

It’s pricey but worth it.

 

[Salty]

If you are only going to do one thing to a part, I’d choose alodine. Then if you want to prime some things as well, do that after the alodine.

 

[ibgarrett]

Thanks everyone. The main parts I'm looking to alodine are the interior to things like the wings/control surfaces. I'm not looking to do anything exterior as (at least in my thinking) anything exterior would show up visibly a lot easier and also (in theory) be a lot more straight forward of a repair than if the ribs were to become corroded.

My main concerns are the mating surfaces between the ribs and the skin being dissimilar materials on contact (alodine vs. the self-etching) and having an issue between the two. The epoxy primer is interesting. The lions share of the folks building the SlingTsi that I've encountered are going the self-etching route, so I was just following suit.

This getting started business is the hardest part as I just want to make sure I do it right when there is no right or wrong way to do things.

 

[wilkersk]

I hate Alodine/Bonderite. I saw plenty of that stuff in the Navy. It is nasty stuff. And, it can be expensive and difficult to dispose of legally. The fines for disposing of it illegally are pretty stiff.

Check this stuff out: https://www.aircraftspruce.com/catalog/cspages/prekotesurface.php

That being said, I scuffed and primed with SEM self-etch gray the entire interior of my RV-8. The wear surfaces and instrument panel in the cockpit and baggage compartments will get epoxy matt finish clear coat over the SEM.

 

[Bell206]

The main parts I'm looking to alodine are the interior to things like the wings/control surfaces.

FYI: when I had rebuilt Cessna 100 series wings, we would Alumipep/Alodine all the individual ribs, skins, spars, etc first then spray everything with a light color epoxy primer. Once reassembled made for easy inspection of the interior wing surfaces.

mating surfaces between the ribs and the skin being dissimilar materials on contact (alodine vs. the self-etching)

Don't quite follow on the "dissimilar materials" comment. Are your skins and ribs of different metals/materials? You don't get into "dissimilar" issues unless the contacting metals or materials have differing Anodic Indexes which causes galvanic corrosion issues. Alodine and most primers do not prevent galvanic corrosion and require other preventative barriers.

 

[German guy]

I hate Alodine/Bonderite. I saw plenty of that stuff in the Navy. It is nasty stuff. And, it can be expensive and difficult to dispose of legally. The fines for disposing of it illegally are pretty stiff. [...]

^^^^^ This. Plus, you would poison the drinking water system, if you would just flush it down the drain.

For the vast majority of applications, scuffing, cleaning and priming with a good Epoxy primer is a much better choice.

This is also what car manufacturers are using and nowadays a lot of aluminum is used on cars. I would guess that what is good for a Cadillac on salty Michigan roads should be more than good enough for a pampered aircraft... ;-)

[...] That being said, I scuffed and primed with SEM self-etch gray the entire interior of my RV-8. The wear surfaces and instrument panel in the cockpit and baggage compartments will get epoxy matt finish clear coat over the SEM.

Too late now, but SEM self-etching primer can be tricky to spray over. You might want to spray a sample first, before you go to work in your cockpit.