How to Handle/Fix Surface Corrosion

[George]

Hi All..

Small area of hangar rash right tip of my elevator. The paint has chipped off in this area and is about the size of a quarter. It appears there is the beginning of some surface corrosion on the bare aluminum. What is the best way to handle/fix this area  of concern?

Added the Pic below...

Thanks for all the suggestions

 

Hank

Edited December 30, 2018 by George
Add Pic

[N201MKTurbo]

Well, back in the day I would tell you to clean it with scotch brite and either paint it with zinc chromate or alodine it. But hexavalent chrome is politically incorrect these days, so give it a little spritz of that zinc phosphate primer, which takes about two weeks to dry and you will be fine. Find the closest color Krylon and give it a little paint. As long as you don’t put on any more paint than chipped off, I wouldn’t worry about balance.

Or, you could pull the elevator, have it stripped and repainted by a professional shop and have an A&P re-check the balance. 

One is going to cost about $15 bucks the other about 1 AMU.

Edited December 28, 2018 by N201MKTurbo

[Bartman]

I had a small area like that on top of the cabin about 3 inches by 1 inch.  I used the Scotch Brite and Alodine and found a rattle can that matched the base white. I could give you 30 minutes and bet money you can’t find it. 

[carusoam]

Always post a pic, in the event there is something there that somebody else can see...

Best regards,

-a-

[FloridaMan]

Instead of a scotch bright, use a Harbor Freight soda blaster, mask off the area and blast all the black stuff out of the pitting. Putting the tip of the blaster inside the cone of a hose spray according to another member here works well for keeping the blast under control. Then do what everyone else said as follow-up. 

[PT20J]

Sand to remove corrosion and feather paint edges. Prime with etch primer (better adhesion than zinc phosphate). Take the access panel from the tailcone to an auto paint shop and they can color match it and put it in a spray can. 

[RobertGary1]

Sand lightly. You don’t want to remove the factory anti-corrosion. 

 

-Robert 

[N201MKTurbo]

12 hours ago, PT20J said:

Sand to remove corrosion and feather paint edges. Prime with etch primer (better adhesion than zinc phosphate). Take the access panel from the tailcone to an auto paint shop and they can color match it and put it in a spray can. 

The zinc phosphate is an anti-corrosion primer. Etch primer is actually corrosive. 

43-13-1b has a whole chapter on remeadation of corrosion. It is a good read.

[PT20J]

1 hour ago, N201MKTurbo said:

The zinc phosphate is an anti-corrosion primer. Etch primer is actually corrosive. 

Well, actually zinc phosphate is an etch primer. https://www.aircraftspruce.com/catalog/pdf/09-02128tds.pdf

I've tried a couple of brands zinc phosphate in spray cans without good results. Both took over a day to dry and spit out little blobs of paint mixed with the spray no matter how long I shook the can. 

SEM lists its etch primer as an aerospace product. https://www.semproducts.com/manage/html/public/content/techsheets/sem_tds_self_etching_primer.pdf

I'm not a paint expert, but I've had good results with this for touch ups.

[N201MKTurbo]

1 minute ago, PT20J said:

Well, actually zinc phosphate is an etch primer. https://www.aircraftspruce.com/catalog/pdf/09-02128tds.pdf

I've tried a couple of brands zinc phosphate in spray cans without good results. Both took over a day to dry and spit out little blobs of paint mixed with the spray no matter how long I shook the can. 

SEM lists its etch primer as an aerospace product. https://www.semproducts.com/manage/html/public/content/techsheets/sem_tds_self_etching_primer.pdf

I'm not a paint expert, but I've had good results with this for touch ups.

I know I hate the zinc phosphate. I loved the zinc chromate. you could put on a nice thin coat and it dried in a minute or so. It is very hard to come by anymore.

[EricJ]

1 hour ago, N201MKTurbo said:

I know I hate the zinc phosphate. I loved the zinc chromate. you could put on a nice thin coat and it dried in a minute or so. It is very hard to come by anymore.

Aicraft spruce still sells alodine, though, both the 1201 stuff as well as the 1001 that dries clear and apparently people use on unpainted/polished airplanes.

https://www.aircraftspruce.com/catalog/cspages/alodine1201.php

Maxwell's shop fabbed a new belly piece (the one right behind the nose gear) when they did the PPI and initial work on my airplane, but didn't prep or paint it.   I've been meaning to get it off and scotch brite and paint it, but how best to do the anti-corrosion has made me wait a bit.   Plus I'm lazy.   Been leaning toward the 1201 stuff, but it's kinda pricey for no more than I need to do.   Right now it gets continual preservation coatings from my oil leak.

[Guest]

1 hour ago, N201MKTurbo said:

I know I hate the zinc phosphate. I loved the zinc chromate. you could put on a nice thin coat and it dried in a minute or so. It is very hard to come by anymore.

Strangely it’s still available in Canada.

https://www.canadiantire.ca/en/pdp/dupli-color-zinc-chromate-primer-0471018p.html

Clarence

[PT20J]

1 hour ago, M20Doc said:

Strangely it’s still available in Canada.

Zinc chromate has fallen out of favor since it is highly toxic and a carcinogen. Interesting, since FED SPEC TT-P-1757A says:

"3.3.2 Toxicity. The manufacturer shall certify that the primer contains no substances of known toxicity under normal conditions of usage." 

Guess it never meet spec ;-)

TT-P-1757A.pdf

[M20S Driver]

2 hours ago, M20Doc said:

Strangely it’s still available in Canada.

https://www.canadiantire.ca/en/pdp/dupli-color-zinc-chromate-primer-0471018p.html

Clarence

You can buy Zinc Chromate on Amazon.

https://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias%3Daps&field-keywords=zinc+chromate

[Igor_U]

I am not sure why would you use either of those. All serious aircraft OEMs (and their vendors) use epoxy primer for decades.

[RLCarter]

Zink Chromate is still available through Aicraft Spruce HERE, just use the drop downs menus and get what you want

[RobertGary1]

19 minutes ago, RLCarter said:

Zink Chromate is still available through Aicraft Spruce HERE, just use the drop downs menus and get what you want

Probably need a Puerto Rico address or something to receive it. Cant mail anything like that to California. 

-Robert 

[M20S Driver]

2 hours ago, RobertGary1 said:

Probably need a Puerto Rico address or something to receive it. Cant mail anything like that to California. 

-Robert 

My friend bought it from Amazon and it was delivered in Northern CA.  

[PT20J]

1 hour ago, Igor_U said:

I am not sure why would you use either of those. All serious aircraft OEMs (and their vendors) use epoxy primer for decades.

Agree epoxy is probably best. My Mooney Service Manual calls for cleaning bare aluminum with solvent, then using a wash primer, then epoxy primer, then the top coat. The wash primer is a low build etch primer. That’s a lot of work for a touch up. You have to mix the epoxy primer and use a spray gun. You can get it in a rattle can, but once you push the button you have a limited time to use it. So, for a touch up, you’ll waste most of the can. Since you need to use an etch primer of some sort to get good adhesion, I like to keep it as simple as possible. So, I just go for an etch primer and a top coat.  But that’s just me. I know guys at museums that will go all out on a chip. 

[bradp]

You can get a hobbyist airbrush for an application like this and get half decent results. 

You can buy two part touch up paint in Matterhorn white or whatever for the top coat in little mustard packs that cover a square foot or so. 

[RobertGary1]

Technically if you put anything on a control surface (even paint) don’t you need to remove it and check balance?

 

-Robert 

[Captnmack]

On 12/28/2018 at 7:26 PM, PT20J said:

Zinc chromate has fallen out of favor since it is highly toxic and a carcinogen. Interesting, since FED SPEC TT-P-1757A says:

"3.3.2 Toxicity. The manufacturer shall certify that the primer contains no substances of known toxicity under normal conditions of usage." 

Guess it never meet spec ;-)

TT-P-1757A.pdf

Well heck, So is MEK!,