scsmith
Well Known Member
We had to prime a whole bunch of aluminum parts for the stub spars and flap and aileron hinges for our tapered composite RV wings.
I really did not want to use alodine because of the severe environmental issues. (it is hexavalent chromium, which is about like dioxin or plutonium)
The gold standard nowadays is AC-130 Sol Gel, but unfortunately I could only find it in rediculously large quantities that would be enough to treat a B-737, so
...
The alternative we chose was PreKote. They don't tell you much about what it is or how it works, just that it works well. The instructions say to wet the aluminum with PreKote and scrub with a maroon scotchbrite until you raise a grey lather, then apply more PreKote and repeat.
The test for adequate scrubbing is that fresh water should sheet off the part without beading up or even breaking the film. Right. Good luck with that. On the 2024 aluminum parts, we were reasonably successful at obtaining a 'reasonably' break-free film sheeting of fresh water. But on the 7075 aluminum parts, no hope. You could stand and scrub and make grey lather all day long, and fresh water still mostly does not wet the surface on rinse. Multiple repeat cycles, same result.
We primed everything with AKZO (thanks to Dave Howe for splitting a purchase) which of course sticks great. But AKZO pretty much sticks great to anything. So that is no testament for the PreKote.
Beyond the corrosion protection of the AKZO itself, it is not at all clear to me that the PreKote does anything at all. Like I said, they tell you nothing about what it is and what it does.
So, I don't know.....we could probably have just scrubbed everything with acetone and scotchbrite and primed and had the same results. It was a long day of scrubbing grey lather on many many parts, and I just don't know if it was worth the trouble at all.
Next time - AC-130 Sol Gel.
I really did not want to use alodine because of the severe environmental issues. (it is hexavalent chromium, which is about like dioxin or plutonium)
The gold standard nowadays is AC-130 Sol Gel, but unfortunately I could only find it in rediculously large quantities that would be enough to treat a B-737, so
...
The alternative we chose was PreKote. They don't tell you much about what it is or how it works, just that it works well. The instructions say to wet the aluminum with PreKote and scrub with a maroon scotchbrite until you raise a grey lather, then apply more PreKote and repeat.
The test for adequate scrubbing is that fresh water should sheet off the part without beading up or even breaking the film. Right. Good luck with that. On the 2024 aluminum parts, we were reasonably successful at obtaining a 'reasonably' break-free film sheeting of fresh water. But on the 7075 aluminum parts, no hope. You could stand and scrub and make grey lather all day long, and fresh water still mostly does not wet the surface on rinse. Multiple repeat cycles, same result.
We primed everything with AKZO (thanks to Dave Howe for splitting a purchase) which of course sticks great. But AKZO pretty much sticks great to anything. So that is no testament for the PreKote.
Beyond the corrosion protection of the AKZO itself, it is not at all clear to me that the PreKote does anything at all. Like I said, they tell you nothing about what it is and what it does.
So, I don't know.....we could probably have just scrubbed everything with acetone and scotchbrite and primed and had the same results. It was a long day of scrubbing grey lather on many many parts, and I just don't know if it was worth the trouble at all.
Next time - AC-130 Sol Gel.