Interior AL surface protection

[etemplet]

I have the interior out of my 150 and I would like to put some type of coating while I have access I am almost finished scuffing and cleaning the aluminum.

I've did lots of research on Alodine and do not feel comfortable putting that on the interior. My main reason is that there is no way I can be 100% sure that all of the Alodine is out of the lap joints and difficult to reach areas. I also read about Corrosion-X but would like something more permanent that doesn't leak out of the seams.

I purchased Zinc Chromate which I plan to use. I was instructed to spay a very light coat of Zinc on the surface. How do I prep for the Zinc coating

I would appreciate some input with options. If it works well... I'll skinny down the tail section and see how far I can get.

Thanks for any help !!

 

[etemplet]

A few shots of the interior,

 

[Silvaire]

Leave it alone, you're going to make a mess and probably knock five years off your lifespan by crawling up in there and spraying Chromate. The aluminum is Alclad meaning it has a layer of pure aluminum on the surface which has a natural corrosion resistance. Don't scrub or sand on it.

Look, it's made it through the past 40 years okay. Don't try to fix what ain't broke.

 

[etemplet]

I am looking for suggestions on a coating or some type of preventative treatment that will be effective in keeping the metal in its current condition which is not perfect. There is what I would call light pitting on the roof area but the A&P says it is not anything serious. I do have a couple of places where corrosion is present. I believe the left kick panel shows a picture of corrosion.

I will do something about it and I would appreciate some input on various ways to address it. I don't like the idea of Corrosion-X because of what read about it but... if that is the best method, sobeit. I live in Louisiana where humidity is generally very high.

 

[Henning]

Use the Corrosion-X, depending on where you live, repeat each annual.

 

[Checkout_my_Six]

If you must.....scrub with Scotchbrite pads then do the Alodine etch treatments....degrease by wiping with denatured alcohol.....then spray with zinc chromate.

 

[OkieAviator]

If you must.....scrub with Scotchbrite pads then do the Alodine etch treatments....degrease by wiping with denatured alcohol.....then spray with zinc chromate.

On my door panels that I recovered I scrubbed them down, wiped them off and sprayed primer on them. Then recovered them, they weren't that bad and I figured if I jacked them up it's just the door panels.

I'm close to removing the rest of the plastics and carpet and if I find patches of corrosion can I just Scotch Brite it lightly and then call it a day? Or if I'm not going to spray it with Zinc Chromate should I leave it alone?

 

[Dan Thomas]

Corrosion makes millions of tiny pits in the surface. Scotchbriting just takes off the crap on the high spots and leaves it in the low spots, where corrosion continues. Acid-etching is used to clean out all of the corrosion products, after that it's alodining to stabilize the surface, and then prime. Shooting prime without doing the proper prep is a waste of time and money.

Better to get some ACF-50 and spray that in there; it wicks into lap joints and penetrates the corrosion and lifts out any moisture and stops further corrosion. Messy stuff, though.

Dan

 

[frfly172]

I'd go with corrosion x at annuals,used it on my 172, worked fine,it does wick out to the seams,I thought that was a good idea.

 

[Jeff Oslick]

Apply a self-etching zinc chromate primer.

e.g.: http://www.aircraftspruce.com/catalog/cspages/duplicolor_selfetchingprimer.php?clickkey=12077

 

[bnt83]

As usual, read the maintenance manual. Don't have one? Get one. Cessna has several different corrosion inhibiting compounds in there.

Ardox AV8 penetrates and dries.

Zinc chromate isn't what it used to be.

 

[bnt83]

Apply a self-etching zinc chromate primer.

e.g.: http://www.aircraftspruce.com/catalog/cspages/duplicolor_selfetchingprimer.php?clickkey=12077

Personally I wouldn't. Its not durable. Look in some of these 1960's era Cessnas that were factory zinc and often its flaking and messy.

http://www.vansairforce.com/community/showthread.php?t=104845&highlight=eastwood&page=2

 

[OkieAviator]

As usual, read the maintenance manual. Don't have one? Get one.

I have the 1977 172N Maintenance manual... is this what you're talking about? I'm hoping that there has been some progress in chemical rust based prevention in the last 38 years.

 

[Henning]

Aluminum is best left bare with its oxide coat to protect it, aluminum doesn't particularly like to be coated. A bare aluminum hull on a boat does better than a painted one when it comes to corrosion. Just use one of the corrosion treatments regularly, they are all effective.

 

[bnt83]

I have the 1977 172N Maintenance manual... is this what you're talking about? I'm hoping that there has been some progress in chemical rust based prevention in the last 38 years.

Are you aware that manuals get revised? Sure you can buy the original issue from 1976 off ebay for $10 but its probably been revised over dozen times since.

Cessna added over 150 pages of corrosion information, including prevention.

 

[OkieAviator]

No didn't know that. Just came with the plane and I think it's the original one. I'll see if I can find a new revised on scanned into a PDF somewhere.

 

[Henning]

I have the 1977 172N Maintenance manual... is this what you're talking about? I'm hoping that there has been some progress in chemical rust based prevention in the last 38 years.

Rust? Mmmm, not really, we still use all the same products. 30 years or so ago they started making primer coatings with phosphoric acid in them to convert any remaining rust to magnetite. But aluminum doesn't rust. As for aluminum corrosion prevention products, no, not really. Environmental and Health & Safety laws have eliminated one or two and made a couple less effective, but in general no, the chemistry was worked out long ago and there have been no changes that have developed, at least at any economically feasible level.

 

[Checkout_my_Six]

True, but with aluminum providing a sealing barrier does stop further corrosion....unlike with steel.

Corrosion makes millions of tiny pits in the surface. Scotchbriting just takes off the crap on the high spots and leaves it in the low spots, where corrosion continues. Acid-etching is used to clean out all of the corrosion products, after that it's alodining to stabilize the surface, and then prime. Shooting prime without doing the proper prep is a waste of time and money.

Better to get some ACF-50 and spray that in there; it wicks into lap joints and penetrates the corrosion and lifts out any moisture and stops further corrosion. Messy stuff, though.

Dan

 

[Henning]

True, but with aluminum providing a sealing barrier does stop further corrosion....unlike with steel.

Aluminum provides its own barrier when exposed to oxygen.

 

[Stewartb]

Clean it up as best you can and shoot it with DP40 epoxy primer. My interior is mostly naked so the DP40 is top coated in a beige auto paint, then a custom blend of Zolatone, then a gloss clear coat for durability. Looks great. If you're going back in the a conventional interior just do the DP40 or you favorite 2-part epoxy primer. If you want self-etching you could use Variprime. It works well, too, but I didn't do my interior in it.

 

[Checkout_my_Six]

Aluminum provides its own barrier when exposed to oxygen.

not if the clad is pitted thru....

 

[Jeff Oslick]

Personally I wouldn't. Its not durable. Look in some of these 1960's era Cessnas that were factory zinc and often its flaking and messy.

http://www.vansairforce.com/community/showthread.php?t=104845&highlight=eastwood&page=2

I used it on our interior about 8 years ago. Had to remove those sound-deadening panels Cessna put in before the hydrophilic glue they used caused corrosion, which meant some scuffing was needed so the Al coating was stripped. Just had the interior all opened up for our annual, and the primer looks exactly the same as when I painted it 8 years ago. As with any paint job, the prep time is the key.

Yes, I wore an air-purifying respirator while painting, and had masked all the windows and the entire instrument panel (including under the panel).

 

[Stewartb]

Removing the old glue is a pain. the best thing I found to soften and lift it was enamel reducer and a plastic scraper. No alclad needs to be removed and it won't be if you stick with a plastic blade.

 

[James331]

Aluminum is best left bare with its oxide coat to protect it, aluminum doesn't particularly like to be coated. A bare aluminum hull on a boat does better than a painted one when it comes to corrosion. Just use one of the corrosion treatments regularly, they are all effective.

Then why are factory seaplanes coated?

 

[Jeff Oslick]

Removing the old glue is a pain. the best thing I found to soften and lift it was enamel reducer and a plastic scraper. No alclad needs to be removed and it won't be if you stick with a plastic blade.

I found goo-gone and a plastic scraper worked ok in most spots, but not all. There were spots where some corrosion had already started, and those needed more treatment.

 

[Stewartb]

Zinc chromate is sacrificial. It literally wears out. My own primer, after 35 years, got no respect as an important component to protect.

 

[Henning]

not if the clad is pitted thru....

Every aluminum alloy I am aware of forms an oxide coating.

 

[Henning]

Then why are factory seaplanes coated?

So the zinc is sacrificial in the corrosion process rather than the aluminum. It doesn't prevent corrosion, it controls the result of it for a limited amount of time. You'll notice the Navy uses a crap load of corrosion prevention treatment even with zinc chromate. Primers do not provide a seal, you need to use a top coat to have a corrosion prevention effect, but these coatings don't like to stick, it's a tenuous bond. As soon as the seal is breached in any way, corrosion will start and lift the paint off, at that point you create an incubator for corrosion. That's why your seaplane isn't painted inside, nor are the Navy's plane's and they use a corrosion inhibitor for prevention.

 

[bnt83]

I used it on our interior about 8 years ago. Had to remove those sound-deadening panels Cessna put in before the hydrophilic glue they used caused corrosion, which meant some scuffing was needed so the Al coating was stripped. Just had the interior all opened up for our annual, and the primer looks exactly the same as when I painted it 8 years ago. As with any paint job, the prep time is the key.

Yes, I wore an air-purifying respirator while painting, and had masked all the windows and the entire instrument panel (including under the panel).

Or you could have poured some AV8 Ardox in a cup and brushed it over your blended areas.

There are many ways to do things. FAA approved repair drawings usually say MIL-LTD-5541 alodined then primed with akzo nobel primer 10P8-11, again, for small areas, brushed on is fine but spray looks nicer.

http://www.anac.com/TDSWeb/ProcessDocuments/AkzoNobel_Alumigrip_10P8-11.pdf

 

[Jeff Oslick]

Or you could have poured some AV8 Ardox in a cup and brushed it over your blended areas.

There are many ways to do things. FAA approved repair drawings usually say MIL-LTD-5541 alodined then primed with akzo nobel primer 10P8-11, again, for small areas, brushed on is fine but spray looks nicer.

http://www.anac.com/TDSWeb/ProcessDocuments/AkzoNobel_Alumigrip_10P8-11.pdf

For the fabric-covered Al panels that were removed, stripped and recovered, I used an alodine process on the bare sheets. That was because I could control where the alodine and the rinse went (i.e., not in the airplane).

 

[bluerooster]

Leave it alone, you're going to make a mess and probably knock five years off your lifespan by crawling up in there and spraying Chromate. The aluminum is Alclad meaning it has a layer of pure aluminum on the surface which has a natural corrosion resistance. Don't scrub or sand on it.

Look, it's made it through the past 40 years okay. Don't try to fix what ain't broke.

Too late, he'd done that prior to his posting.

 

[Tom-D]

Leave it alone, you're going to make a mess and probably knock five years off your lifespan by crawling up in there and spraying Chromate. The aluminum is Alclad meaning it has a layer of pure aluminum on the surface which has a natural corrosion resistance. Don't scrub or sand on it.

Look, it's made it through the past 40 years okay. Don't try to fix what ain't broke.

X 2,, I use http://www.amazon.com/CRC-06026-Heavy-Corrosion-Inhibitor/dp/B0000AXYA0

a light coat. forget the paint unless you etch and re-alodine

 

[Tom-D]

Then why are factory seaplanes coated?

In that era that's the best they had.

In real seaplanes like the P-5M we hung tea bags full of chromate crystal in the bilge water to try to stop the corrosion progress, but when we could get them out of the water we would dry the bilges and shoot them with grade 4 paraketone, thinned to spray with a garden sprayer.

 

[Tom-D]

That was because I could control where the alodine and the rinse went (i.e., not in the airplane).

How ??

 

[Henning]

How ??

Take the doors off the plane?

 

[Jeff Oslick]

How ??

Removed from aircraft. I'm not talking about the fuselage skin (for the alodined parts). The fabric covered parts of the side wall come out of the plane.

 

[bnt83]

Removed from aircraft. I'm not talking about the fuselage skin (for the alodined parts). The fabric covered parts of the side wall come out of the plane.

It boggles my mind how those panels can come out basically spotless but a 177/210 carry thru spar can be trashed from foam & glue.

Had a Falcon 50 in once that was crazy. Dassault put a foam block by the nose gear fittings and sealed over it to make a water/moisture dam. The sealant had cracks it allowing the foam to absorb moisture. The results were quite impressive.

 

[Dan Thomas]

Every aluminum alloy I am aware of forms an oxide coating.

It will, but 2024T3 is Alcad because of its copper content. All 2000 series use copper as the chief alloying element, and its presence makes the aluminum corrode aggressively once it's exposed. The Alclad is a thin (2% of total thickness) coating of pure aluminum that will oxidize and form a relatively inert barrier, with "relatively" being important. It will corrode, just more slowly.

Anywhere the Alclad is scratched, corrosion can start and move quickly. Where the metal is drilled, or at the edges of cut sheets, corrosion can start.

Seaplanes are chromated before the parts are assembled. There is no point priming the interior of a finished airplane; the important parts, like the edges of sheets at lap seams and the rivet holes in those seams and under stringers and bulkheads don't get covered if it's sprayed after assembly. In float work, the structures guys often dip the rivets in chromate before driving them, just to minimize corrosion from the hole's edges.

Many years ago I was involved in air brake remanufacturing. All the control valves, compressors, and brake actuators used in heavy trucks and earthmoving machinery. The brake actuators, depending on manufacturer, were often aluminum castings containing diaphragms and a huge spring that acted as an emergency/park brake when the air compressing the spring was released. One manufacturer (Wagner) made their castings from a high-copper-content aluminum to save material and increase strength, but the water (and often salt) on the roads caused it to corrode at an amazing rate and those big springs would blow out and fly out from under the truck and kill people behind it. Or mechanics working on it. We were scared of them when they showed up in core shipments and used to stick them in the hydraulic press right away, in a cage, and crush them and let that spring relax.

Like anything i aviation, the alloys are a compromise. We need strength so we can reduce thickness and therefore weight, but the price can be sensitivity to corrosion and cracking.


Dan

 

[Stewartb]

Some pictures of my interior removal and what's left after rub-a-dud-dubbing for a couple of afternoons with enamel reducer. Once cleaned up and all the loose stuff was removed it was shot with DP-40 and zolatone, fitted with foam insert panels, and the panels upholstered. Almost 5 years later it looks like new.

 

[Tom-D]

Removed from aircraft. I'm not talking about the fuselage skin (for the alodined parts). The fabric covered parts of the side wall come out of the plane.

And you kept the aluminum sheet panels? Should have simply sent them to Stich.

http://www.recovery-shop.com