Fixing small corrosion spots

[AaronC]

On our C, we have a few corrosion spots under the paint that we want to repair... nothing major, just want to get ahead of it. Any tips from those that have done it? The rest of the paint is in really great shape, so there's no need to repaint the whole thing.

[N201MKTurbo]

I would peel off the paint blister, scotch brite the metal until it is shiny, then paint the bare metal with an anti corrosion paint. After that paint dries touch up with matching paint.

[jasona900]

I have a few spots of filiform corrosion that likely resulted from poor preparation when the airplane was painted.   When I was researching the correct way to treat the corrosion, I found this article:  http://www.sweethaven02.com/Aviation/MaintHandbook/FAA-8083-30_Ch06.pdf

I think it does a good job explaining the different types of corrosion, and the proper way to treat it.  I have been told by several mechanics that if the corrosion is not completely removed, and the aluminum isn't properly treated prior to painting, the corrosion will return.

I also went to a local auto paint store, and was shocked how much a pint of paint, and the necessary activator would cost.  Add that to the cost of the chemical to anodize the aluminum, and I decided to just let the shop take care of it during annual.  I was never really that good at painting and blending anyways.

[carusoam]

If the paint is original...

And the plane has been stored outside...

The paint gets thinner and thinner with oxidation and each wash and wax....

Certain spots are under a bit more stress while flying and probably see more wear...

My 65C would get some spots sanded down to bare metal.  Alodyned and painted with a spray can of an amazingly close match...

One thing you can do is take some access panels to autobody paint place to have the color matched and buy some paint from them.

It helps to know what type of paint you have on there already.  Maintenance manuals and log books may hold the key to that mystery...

PP thoughts only...

Best regards,

-a-

[jetdriven]

Abrade the corrosion away with a nylox wheel on a drill. Finish up with red scotchbrite. Then prep with PreKote. Then a thin layer of phosphate or etching primer then a thin topcoat of 2-part urethane paint such as Nason Full-thane. A spot smaller than1.5-2” you can brush it. Larger needs to be sprayed for the best look. Don’t forget to roll tape it to prevent the edge. 

Also, get the color scanned at matched at a Finishmaster. O’reilly auto can’t match paint, their system is crap. 

Edited January 28, 2018 by jetdriven

[DonMuncy]

1 hour ago, jetdriven said:

Abrade the corrosion away with a nylox wheel on a drill. Finish up with red scotchbrite. Then prep with PreKote. Then a thin layer of phosphate or etching primer then a thin topcoat of 2-part urethane paint such as Nason Full-thane. A spot smaller than1.5-2” you can brush it. Larger needs to be sprayed for the best look. Don’t forget to roll tape it to prevent the edge. 

Also, get the color scanned at matched at a Finishmaster. O’reilly auto can’t match paint, their system is crap. 

I'm not familiar with roll tape. How do you do that?

[AaronC]

Yah, can you elaborate on the roll tape?

Thanks for the help guys.

[MB65E]

6 hours ago, jasona900 said:

I have a few spots of filiform corrosion that likely resulted from poor preparation when the airplane was painted.   When I was researching the correct way to treat the corrosion, I found this article:  http://www.sweethaven02.com/Aviation/MaintHandbook/FAA-8083-30_Ch06.pdf

I think it does a good job explaining the different types of corrosion, and the proper way to treat it.  I have been told by several mechanics that if the corrosion is not completely removed, and the aluminum isn't properly treated prior to painting, the corrosion will return.

I also went to a local auto paint store, and was shocked how much a pint of paint, and the necessary activator would cost.  Add that to the cost of the chemical to anodize the aluminum, and I decided to just let the shop take care of it during annual.  I was never really that good at painting and blending anyways.

Excellent link! That's better than anything the FAA has ever produced! 

-Matt

[jetdriven]

4 hours ago, DonMuncy said:

I'm not familiar with roll tape. How do you do that?

This shows it pretty well. Basically keep the paint gun 90 degrees to the surface and do not lay the paint on very heavy at all near the tape line. Actually for a pro job, spray the final coats from over the masked part and down at a 45 towards the work. Roll  the tape 1/8” back and spray the last coat over-thinned. Then when it dries blend the line by hand with a very fine buffing compound such as 3M Imperial hand glaze and a terry cloth towel. Done right the repair is nearly invisible. I’ve done this a few times.  

 

Edited January 28, 2018 by jetdriven

[DonMuncy]

Thanks, very nice.

[201Steve]

I took a stab at cleaning up some corrosion spots today with the general guidance of @jetdriven suggestion. Instead of a nylox wheel which I didn’t have on hand, I used a plastic scraper tool and then cleaned up with maroon scotch brite. 
 

1) scrape flaky paint off with plastic scraper. 
2)Bring aluminum to shiny with maroon scotch brite. 
3) clean up the aluminum dust with low concentration simple green aviation. 
4) Apply Prekote

5) self etching primer

6) finish paint. 
 

a couple thoughts that I’ll need to review before I get back on it, to make better use of my time. 
 

1) the “main” spots of corrosion flakes off pretty well with the plastic scraper. However, the trailing tails of filliform are still too well bonded for a scraper. Will not flake off. I understand all of this needs to get removed for maximum effectiveness. What’s the best way to get the paint off of these stubborn spots? Scotch brite directly onto paint does not do much but lightly scuff the paint. Would a nylox wheel get to this? A heavier grit sandpaper or scotch brite? A dremel attachment of some type? Chemical paint remover?  
 

2) I haven’t found as much useful instruction for prekote used as a spot treatment. The most detailed instructions are for whole plane applications. trying for best application while working in small areas. Any videos or write ups appreciated. 
 

3) After scotch brite buffing the bare aluminum shiny, it creates a lot of black dust that gets all over the good paint in the surrounding area. What’s the best way to mitigate or clean this up prior to prekote application? I decided after scotch brite polishing, I would wipe the area down with some low concentration simple green aviation to clean up the area before prekote treatment. Is this acceptable? Wondering if it was a bad idea to apply corrosive simple green prior to a corrosion inhibiting treatment, seems counterintuitive. 
 

any other feedback on the topic appreciated.

 

[jetdriven]

Maybe some real stripper on the area to clean it off before working the corrosion. I'd also hit the spots of corrosion with alumiprep 33 before neutralizing then the preokote. It really gets the corrosion out of the dark pits.  Keep it wet and clean. Then prekote. Then white epoxy primer 

[MikeOH]

@jetdriven

How do you neutralize the Alumiprep 33?

[Pinecone]

For smaller areas to touch up, with a hard edge, like a chip, the best way to paint is with an artist brush and fill the chip.

I have watched pros at the BMW factory touch up chips and you can't see the fix.

[jetdriven]

13 hours ago, MikeOH said:

@jetdriven

How do you neutralize the Alumiprep 33?

Baking soda solution.  Then good rinse 

[Fly Boomer]

14 hours ago, jetdriven said:

Maybe some real stripper on the area to clean it off before working the corrosion. I'd also hit the spots of corrosion with alumiprep 33 before neutralizing then the preokote. It really gets the corrosion out of the dark pits.  Keep it wet and clean. Then prekote. Then white epoxy primer 

How do you prevent the stripper from degrading the good paint surrounding the target environment?

[RoundTwo]

21 hours ago, 201Steve said:

I took a stab at cleaning up some corrosion spots today with the general guidance of @jetdriven suggestion. Instead of a nylox wheel which I didn’t have on hand, I used a plastic scraper tool and then cleaned up with maroon scotch brite. 
 

1) scrape flaky paint off with plastic scraper. 
2)Bring aluminum to shiny with maroon scotch brite. 
3) clean up the aluminum dust with low concentration simple green aviation. 
4) Apply Prekote

5) self etching primer

6) finish paint. 
 

a couple thoughts that I’ll need to review before I get back on it, to make better use of my time. 
 

1) the “main” spots of corrosion flakes off pretty well with the plastic scraper. However, the trailing tails of filliform are still too well bonded for a scraper. Will not flake off. I understand all of this needs to get removed for maximum effectiveness. What’s the best way to get the paint off of these stubborn spots? Scotch brite directly onto paint does not do much but lightly scuff the paint. Would a nylox wheel get to this? A heavier grit sandpaper or scotch brite? A dremel attachment of some type? Chemical paint remover?  
 

2) I haven’t found as much useful instruction for prekote used as a spot treatment. The most detailed instructions are for whole plane applications. trying for best application while working in small areas. Any videos or write ups appreciated. 
 

3) After scotch brite buffing the bare aluminum shiny, it creates a lot of black dust that gets all over the good paint in the surrounding area. What’s the best way to mitigate or clean this up prior to prekote application? I decided after scotch brite polishing, I would wipe the area down with some low concentration simple green aviation to clean up the area before prekote treatment. Is this acceptable? Wondering if it was a bad idea to apply corrosive simple green prior to a corrosion inhibiting treatment, seems counterintuitive. 
 

any other feedback on the topic appreciated.

 

For my filiform corrosion, after initial paint removal, I use scotchbrite dipped in Alumaprep 33. It helps the SB cut better and preps the aluminum at the same time. Rinse, Alodine and then paint as desired. I’m headed to paint not too far in the future, so this is just stop gap to get the corrosion under control until then. 

[201Steve]

I’ve been reading quite a bit on painting and golly, there’s a million opinions out there. It’s a full on war in some discussions in other forums. Chromate, alodine, pre kote, epoxy primer, etching primer, stainless steel brushes, sand paper, scotch brite, Al clad, etc etc etc. The primer debate is hot hot hot

[RoundTwo]

On 5/29/2023 at 9:08 PM, 201Steve said:

I’ve been reading quite a bit on painting and golly, there’s a million opinions out there. It’s a full on war in some discussions in other forums. Chromate, alodine, pre kote, epoxy primer, etching primer, stainless steel brushes, sand paper, scotch brite, Al clad, etc etc etc. The primer debate is hot hot hot

Like so many other topics, there are multiple ways to skin a cat.