Fuel tank exterior priming: before/after assembly or not at all?

[DonMcKee]

For those of you in the primer camp, I'm wondering what you did with the outside of the fuel tanks (i.e.. anywhere that won't be in direct contact with fuel or Proseal). Did you mask and prime before assembly, wait until after assembly, or elect to leave the tanks bare? Any pros/cons/gotchas that you ran into using your chosen treatment? If you primed before assembly, in the areas where a finishing fillet of Proseal is applied (like around the Z-brackets on the tank baffles), did you make sure there was no primer under the fillet, or were you only concerned with keeping primer away from the fay surfaces themselves?

If it's relevant, I'm building an RV-14A, and using Stewart Systems EkoPrime water-based, one-part, primer (perhaps not the best choice to use anywhere near fuel, but, hey, I'm not going to have any leaks ).

Thanks for any insight you can provide!

 

[Ralph Inkster]

I leave exterior (& interiors) of my tanks bare. The skins get prime & paint when the rest of the plane is painted. The ribs, rear baffle & Z brackets are left natural in case future maintenance is needed in these areas. I have never seen corrosion in these areas on the many tanks I’ve worked on.

 

[skelrad]

Same as Ralph. I've primed virtually everything else, but really see no reason to prime the tanks. The possibility of needing to fix future leaks is just made easier if there is no primer to deal with.

 

[dwollen89]

I primed my z brackets because they’re not alclad. Otherwise, don’t prime anything else.

 

[bertschb]

For those of you in the primer camp, I'm wondering what you did with the outside of the fuel tanks (i.e.. anywhere that won't be in direct contact with fuel or Proseal). Did you mask and prime before assembly, wait until after assembly, or elect to leave the tanks bare?

The fuel tank is the only part of the airplane I didn't prime with Akzo. I didn't want to mask and prime exposed parts before assembly because I wanted to make sure everything was bare metal so the tank sealant would adhere better- mainly just the areas around the outside perimeter where parts are riveted together. I didn't want to mask and prime the completed assembly afterwards because....I was lazy

 

[DonMcKee]

I have never seen corrosion in these areas on the many tanks I’ve worked on.

The possibility of needing to fix future leaks is just made easier if there is no primer to deal with.

I primed my z brackets because they’re not alclad.

I didn't want to mask and prime the completed assembly afterwards because....I was lazy

Thanks, all, for the feedback! Your thoughts make me more comfortable with skipping priming the tanks altogether (except maybe the Zees). Woo hoo!

 

[dmn056]

I Alodined all my tank components. Apart from the corrosion protection it provides, Alodine also provides a better adhesive base for Proseal than bare Alclad.

 

[fixnflyguy]

Prime 100%..Akzo or similar. I alodined and primed everything. As a structures specialist in the heavy jet industry for 45 years, I can't do it any other way. The only naked metal on my RV4 is the baffles..Alodine only on them. Priming over sealed assemblies is ok , and exactly what I did on my build. I live by the Boeing and Airbus procedures, and spent too much time on aging aircraft and corrosion prevention committees.

 

[Little Al]

I Alodined all my tank components. Apart from the corrosion protection it provides, Alodine also provides a better adhesive base for Proseal than bare Alclad.

View attachment 80530

I did the same