I'd like your opinion on my corrosion treatment

[rbridges]

I had a previous post that showed some possible galvanic corrosion near the rear seat belt attachment and the rear seat legs.  I talked with my IA and Joey Cole.  I ended up removing the seat bottoms but not the seat posts.  I remove the inspection plates from the floor and looked around.  I sanded the aluminum floor panel and the steel foot posts/attachments as best I could.  I added aluminum tape around the panel edges and sprayed zinc chromate everywhere that I could.  I could not remove all the rust/oxidation, but won't the zinc chromate seal it?  Looking at the pics, does it look like this will do?

[rbridges]

this is the rear seatbelt attachment to the floor panel.  I looked at the nut/bolt on the other side of the floor panel with a mirror, and everything looks clean.  I'm assuming the oxidation was limited to the top surface.  

[Browncbr1]

It is my understanding that zinc chromate is a rust inhibitor only. Not a rust converter.   If you spray it over rust, it just encapsulates corrosion that will continue to be active.  Eastwood and permatex both make rust converters in various forms.   For hard to access areas like yours, I would use the Eastwood aerosol version.   But, it is worth the effort to get in with a small Dremel sanding ball and get as much as possible first.   Any rust will turn completely black, which is what they claim confirms the rust is now dormant.  Then, spray over it with zinc or paint.  If this isn't done before zinc or paint, it will eventually bubble and flake down the road.  

Heres a link to the Eastwood stuff 

http://www.eastwood.com/eastwood-rust-converter.html?SRCCODE=TXT00010&adpos=1t1&creative=164110199694&device=m&matchtype=e&network=g&gclid=CNn-opPihtECFdgGgQod4OQKYg

[cliffy]

AC 43.13 1B , 6-136 has all the information you need to treat the aluminum area. Table 6-1 and all of Section 6 has valuable information for you.

[DXB]

I don't know much about corrosion but do know a couple things about cancer biology.  Zinc chromate is a spectacularly powerful carcinogen - a term usually used too lightly in an age where everything is claimed to cause cancer. Please take maximal protective precautions when  spraying the stuff.  

[Yetti]

I am unclear here, but did you tape then zinc chromate,  or zinc chromate then tape, then zinc chromate over the tape?    I don't think needs protecting.

did you sand the alum with aluminum oxide paper?  I think a stainless brush is also OK.  It is OK for prepping alum for welding.

[carusoam]

Sealing over an oxidized surface will not have the benefit you want it to have.

The oxidation has a tendency to continue while being hidden by a coating.

Think of it like corrosion between layers or stacks of metal.  Done properly the layers get separated, cleaned, and coated before reassembly.  If coating the outside worked, that would be nice...

Consider the inter granular type of corrosion.  This is the type of corrosion that works into the metal between it's granular structure.  This occurs after the surface gets compromised.

all that to say clean and coat the surface properly...

PP advice, not a mechanic...

Best regards,

-a-

[takair]

37 minutes ago, DXB said:

I don't know much about corrosion but do know a couple things about cancer biology.  Zinc chromate is a spectacularly powerful carcinogen - a term usually used too lightly in an age where everything is claimed to cause cancer. Please take maximal protective precautions when  spraying the stuff.  

Thank you for this warning. The industry uses this stuff so loosely and with little precaution.  Would you mind expanding on this?  Is it breathing it or skin contact as well?  I know I've done both.  Does the impact reverse over time?  This is another nice aspect of Mooneyspace, we are all able to learn from each other and from different experiences.

[rbridges]

1 hour ago, DXB said:

I don't know much about corrosion but do know a couple things about cancer biology.  Zinc chromate is a spectacularly powerful carcinogen - a term usually used too lightly in an age where everything is claimed to cause cancer. Please take maximal protective precautions when  spraying the stuff.  

I appreciate the heads up.  I did some reading, and this warning was everywhere!  I took steps to make sure I didn't contact the stuff or breathe it.

[rbridges]

1 hour ago, Browncbr1 said:

It is my understanding that zinc chromate is a rust inhibitor only. Not a rust converter.   If you spray it over rust, it just encapsulates corrosion that will continue to be active.  Eastwood and permatex both make rust converters in various forms.   For hard to access areas like yours, I would use the Eastwood aerosol version.   But, it is worth the effort to get in with a small Dremel sanding ball and get as much as possible first.   Any rust will turn completely black, which is what they claim confirms the rust is now dormant.  Then, spray over it with zinc or paint.  If this isn't done before zinc or paint, it will eventually bubble and flake down the road.  

Heres a link to the Eastwood stuff 

http://www.eastwood.com/eastwood-rust-converter.html?SRCCODE=TXT00010&adpos=1t1&creative=164110199694&device=m&matchtype=e&network=g&gclid=CNn-opPihtECFdgGgQod4OQKYg

I read the same thing, but I was hoping it would keep it from spreading.  I read that zinc chromate would adhere to iron oxide as long as any flaky stuff was removed.  I guess I'll have Joey take a look at things just to make sure.

[carusoam]

Iron oxide changes in volume compared to it's iron starting point.  This change in volume makes it flake and fall away exposing new surfaces to be exposed to oxidizing...

some aluminum alloys are really nice about having the oxide surface be tougher than the aluminum itself.  The volume change isn't enough to make it flake off.  Some aluminum alloys, but not all aluminum alloys...

Apparently, the aluminum used for spars is susceptible to the flaking and falling away type of corrosion that expose the granules even more..,  the white dusty stuff is the equivalent of rust for aluminum.

Again PP kind of knowledge, not a mechanic...  hoping this is helpful in a way.

Best regards,

-a-

[DXB]

39 minutes ago, takair said:

Thank you for this warning. The industry uses this stuff so loosely and with little precaution.  Would you mind expanding on this?  Is it breathing it or skin contact as well?  I know I've done both.  Does the impact reverse over time?  This is another nice aspect of Mooneyspace, we are all able to learn from each other and from different experiences.

Its direct tissue toxicity is strong - I wouldn't want the wet paint on me.  It is also a very powerful toxin and mutagen in vitro at low dose (more my area).  In fact zinc chromate may be the most toxic of the chromate salts. The epidemiologic link between inhaled industrial exposure of chromates and lung cancer in the real world is fairly strong but not bulletproof (not quite as bad as asbestos maybe) - and its use has dropped off quite a bit so may never know for absolute certain - seems real though.  I don't know what makes for an adequate respirator when spraying the stuff, but it seems essential.  It has been studied as a cause of GI cancer in areas with contaminated water supply - here the epidemiology is weak but we are dealing with much lower dose exposures.

[Marauder]

Its direct tissue toxicity is strong - I wouldn't want the wet paint on me.  It is also a very powerful toxin and mutagen in vitro at low dose (more my area).  In fact zinc chromate may be the most toxic of the chromate salts. The epidemiologic link between inhaled industrial exposure of chromates and lung cancer in the real world is fairly strong but not bulletproof (not quite as bad as asbestos maybe) - and its use has dropped off quite a bit so may never know for absolute certain - seems real though.  I don't know what makes for an adequate respirator when spraying the stuff, but it seems essential.  It has been studied as a cause of GI cancer in areas with contaminated water supply - here the epidemiology is weak but we are dealing with much lower dose exposures.

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[Yetti]

Like most AC that one talks about lots of things and covers lots of areas.

Let's try this:

Filiform corrosion on painted exterior say wing skin.or like to OP had with the rear seating surfaces.  The metal on the side bracket I would do different.

I would say Stainless brush to remove corrosion.  Then alum etching  primer, then epoxy paint.   Would this work?

For the metal bracket Tape off all alum surfaces to make sure the Iron does not get on the alum.   sand or brush Good primer and epoxy paint.  Best case the bracket is removed to get to the backside.   Looks like OP only did the front side.  Would this work?

 

[takair]

Regarding the original question, this may slow down propagation of corrosion, but it was never clear what caused it (soda? Mouse urine., etc.) If there is corrosive material sandwiched between the steel leg and the aluminum, that will continue to corrode over time.  It would likely take years, but could happen.  Is it worth removing all the parts to clean and treat?  Hard to say.  Perhaps keep it on the long term to do list.

[rbridges]

Just now, takair said:

Regarding the original question, this may slow down propagation of corrosion, but it was never clear what caused it (soda? Mouse urine., etc.) If there is corrosive material sandwiched between the steel leg and the aluminum, that will continue to corrode over time.  It would likely take years, but could happen.  Is it worth removing all the parts to clean and treat?  Hard to say.  Perhaps keep it on the long term to do list.

No signs of rodents.  The underside was very clean from what I could tell.  When I bought the plane 6 years ago, I noticed the roof would leak when it flew through rain.  I found the drain tube wasn't attached to the air scoop.  The previous owner said he never let anyone bring drinks in the plane and it was hangared.  My best guess is water worked its way to the floor and caused the galvanic corrosion b/t the steel brackets and aluminum floor pan.

I'm hoping what I did will slow things down.  My next annual is in August 2017 timeframe.  I'll have someone remove the seats and brackets completely to evaluate/treat.  IMO, I think this is something that could take forever to become anything, but I don't want to take chances.

[carusoam]

If easy enough give it a look often.  Propagating aluminum oxidation is pretty obvious with the white dust it generates.  If it is generating white dust, this is fix it time.  Waiting can get more expensive quickly.

Things I learned from my private pilot M20C experience.

Best regards,

-a-

[cliffy]

We used to use zinc chromate primers on aluminum mostly Now a days its zinc phosphate primer as the chromates have been legislated out of existance for the most part just like chlorinated hydrocarbons.  Used to use trichlorethylene cleaners all the time but now?

The name  "zinc chromate" is synonymous with all tissues being Kleenex. It was used but now the can reads zinc phosphate. I haven't seen a spray can of chromate for years. Can it still be found?

[rbridges]

12 hours ago, carusoam said:

If easy enough give it a look often.  Propagating aluminum oxidation is pretty obvious with the white dust it generates.  If it is generating white dust, this is fix it time.  Waiting can get more expensive quickly.

Things I learned from my private pilot M20C experience.

Best regards,

-a-

thanks.  Joey Cole said to come in one day, and he would take a look.  I'm going to error on the side of caution.

[rbridges]

3 hours ago, cliffy said:

We used to use zinc chromate primers on aluminum mostly Now a days its zinc phosphate primer as the chromates have been legislated out of existance for the most part just like chlorinated hydrocarbons.  Used to use trichlorethylene cleaners all the time but now?

The name  "zinc chromate" is synonymous with all tissues being Kleenex. It was used but now the can reads zinc phosphate. I haven't seen a spray can of chromate for years. Can it still be found?

Spruce sells it in an aerosol can.  

[cliffy]

Really? I'll look for it   Didn't know it still existed.

[takair]

Cliffy may be right.  The stuff I have been using for years and calling Zinc Chromate actually has Zinc Phosphate on the cans. This is the stuff available from most of the big outlets.

[rbridges]

I've looked at a lot of interior pics, and it seems that many mooneys have oxidized rear seat belt brackets.  Were those not painted from the factory? Or did time just get the best of them?

[takair]

Well, can't argue with the picture.  We may have to chalk this up to "what's good for the Mooney, may not be good for us".  I wonder how Zinc Phosphate compares in performance vs. toxicity?

[cnoe]

Also available on Amazon. https://www.amazon.com/Moeller-Green-Chromate-Primer-Outboard/dp/B000N8LR24/ref=sr_1_1?ie=UTF8&qid=1482589672&sr=8-1&keywords=Zinc+chromate+primer



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