Pacifying/Repairing Corrosion

My RV - 4 has been subjected to dust and damp and is exhibiting some corrosion which has made it's way through the alclad in some small round patches, some small runnels of filimentous corrosion and a general and proably unproblematic dusting of white powder.

I have cleaned off all the dust and the visible white powder with a gentle wipedown with lots of clean water and left to airdry in the hot sun.

I am imagining that I will need to convert or pacify the corrosion to prevent it travelling further before painting over with a primer and finish coat. I can imagine the corrosion going crazy if painted over but not chemicaly neutralised. There are bits where the Scotchbrite has gone through the alclad entirely.

None of this is structural and all involves the bits of skin I had hoped to paint straight away but was side tracked for a couple of years.

One of the pilots I was working with talks about a preperation known colloquially as "Tomato Sauce" which converts the corrosion but must itself be painted over straight away since it has no mechanical integrity and if left exposed after treatment, can actually make things worse.

The reason for making this a seperate thread is that it is a case of getting to the stable door a bit too late.

Thank You in anticipation.

Mark

markabolton at yahoo dot com

I am a big fan of alodine and primer. Chances are the corrosion is just on the surface and the entire plane will be sanded and cleaned before it is painted. I won't worry about it and just make sure you sand all corrosion off and clean all surfaces before you prime/paint. Keep the plane dry. I would use acetone to clean the surfaces since it will evaporate if it gets caught in any crevices unlike water.

Mark Bolton said:

My RV - 4 has been subjected to dust and damp and is exhibiting some corrosion which has made it's way through the alclad in some small round patches, some small runnels of filimentous corrosion and a general and proably unproblematic dusting of white powder.

markabolton at yahoo dot com

Click to expand...

Mark, it's interesting that the primer wars rage on for years with hunderds of builders swearing blind that alclad is all you need. But when some-one reports corrosion there's not a peep to be heard from any of them.

I'd degrease the area and follow up with a scotchbrite 7447 pad to get rid of any white deposits. Then I'd apply Alumiprep (but making sure it doesn't get between any overlapping surfaces, and don't let it dry on the aluminium) and wash it off with huge quantities of running water. Then I'd apply alodine to passivate the surface and prevent further immediate oxidation.

You need to prepare and paint the plane immediately or risk a more widespread problem.

I'm presuming the corrosion is on the outside. If it's inside you've got a much bigger problem.

Nothing to do with Alclad.....

Captain Avgas said:

Mark, it's interesting that the primer wars rage on for years with hunderds of builders swearing blind that alclad is all you need. But when some-one reports corrosion there's not a peep to be heard from any of them.

I'd degrease the area and follow up with a scotchbrite 7447 pad to get rid of any white deposits. Then I'd apply Alumiprep (but making sure it doesn't get between any overlapping surfaces, and don't let it dry on the aluminium) and wash it off with huge quantities of running water. Then I'd apply alodine to passivate the surface and prevent further immediate oxidation.

You need to prepare and paint the plane immediately or risk a more widespread problem.

I'm presuming the corrosion is on the outside. If it's inside you've got a much bigger problem.

Click to expand...

...and everything to do with the environment this airplane was subjected to. Primed and painted airplanes corrode all of the time, while some that never where last several life times with no protection whatsoever.... It's not a war, it is a choice with many factors to consider including the environment the airplane will live in. You might call me a "casual observer" to the primer wars as I wont pick a side....

JonJay said:

...and everything to do with the environment this airplane was subjected to. Primed and painted airplanes corrode all of the time, while some that never where last several life times with no protection whatsoever.... It's not a war, it is a choice with many factors to consider including the environment the airplane will live in. You might call me a "casual observer" to the primer wars as I wont pick a side....

Click to expand...

Yeh yeh you live in Arizona....and you'll NEVER EVER fly to the Caribbean. Nor will you sell the plane to anyone else who doesn't live in a desert and who doesn't promise not to fly to Florida for a beach holiday.

It's Ok not to prime. As you say, it's just another choice. I just wish those who can't be bothered would just admit that they can't be bothered instead of rationalizing their decision with ridiculous anecdotal tales about some unprimed Cessna a friend once saw hangared in Reno that was 40 years old without a spot of corrosion.

Captain Avgas said:

Yeh yeh you live in Arizona....and you'll NEVER EVER fly to the Caribbean. Nor will you sell the plane to anyone else who doesn't live in a desert and who doesn't promise not to fly to Florida for a beach holiday.

ridiculous anecdotal tales about some unprimed Cessna a friend once saw hangared in Reno that was 40 years old without a spot of corrosion.

Click to expand...

was in the shop a couple of days ago and there was a 182 getting a skin replaced, late 70's model. there was a gracious plenty of corrosion on it...the corrosion is most always gonna be between faying surfaces...i wish people would take apart some of those old rags. dont tell me ive seen tooo many of them corroded to ****. but will primer last 30 years is the question? the working of components is going to grind away the paint or alclad if only a couple .001s...i think its a toss up either way. i wont prime the rv3b

Does anyone have any experince with CounterAct? Wonder it it would work on alum to prevent galvanic corrosion.

I've seen it promo'ed on the automotive gearhead shows and looks intriguing. It's basically an electrical corrosion deterrent. Here's a writeup on it: http://www.counteractrust.com/promo events.htm

jmartinez443 said:

Does anyone have any experience with CounterAct? Wonder it it would work on alum to prevent galvanic corrosion.

I've seen it promo'ed on the automotive gearhead shows and looks intriguing. It's basically an electrical corrosion deterrent. Here's a writeup on it: http://www.counteractrust.com/promo events.htm

Click to expand...

I don't know about galvanic corrosion (which there is very limited areas were this could happen on a RV) but I would imagine it could reek havoc on your avionics.

Pits, its the pits.

Just for the pitted spots

Clean the corroded spots that have residue with aluminum jelly and a brand new small stainless welding brush until after rinsing and drying with air you can see no gray or black residue, only clean , albeit pitted, silver colored aluminum.

Then 7448 scotchbrite it by hand with mild soapy water until it is baby bu++ smooth. Rinse, dry, alumiprep, alodine, prime, paint. Fly!

I used to be fixing planes for a living on the Cal coast (Lompoc Ca.) and this was a very common procedure.

I repainted a 172 one time that was so bad I mixed up 2 gallons of homemade aluminum jelly and spayed it on with a garden sprayer after we stripped it. We spent about one full week cleaned the uglies off of her.

I am on the primer side of the war, but believe me, the primer is not worth its weight if the prep is weak.

Best wishes.