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Old 06-22-2021, 10:14 AM
KAndrews KAndrews is offline
Join Date: Jul 2019
Location: Troy, Texas
Posts: 3
Default Possible corrosion on skin?

Good morning,

We have been working on the wings of our RV-10 and ready to put the bottom skins on. This weekend, I noticed overspray from the porta-cool on the skin and it appears to be corrosion. Here are two photos:

I tried cleaning with acetone and MEK. Upon doing so, it knocked off the grit and made the surface smooth, but it looks more cloudy.

I checked the pH of the porta-cool water with hot-tub strips. It is greater than 9.0.

Is this, in fact, corrosion? If so, is there a way to clean it and stop the damage? It has only been on for about 2 weeks time. I am a little concerned that we will button it up and not see it. We have been priming the interior surfaces with SEM Self-etching primer.

Any advice is appreciated!
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Old 06-22-2021, 10:23 AM
nohoflyer nohoflyer is offline
Join Date: Sep 2018
Location: Brooklyn, NY
Posts: 142

I had a very similar thing happen to me. I left my horizontal stab in an area where my leaking refrigerator line slowly dripped on it. Very frustrating.

My solution was to clean it off and scotchbrite the heck out of it to remove the corrosion. The sooner you do this the better so you only have a light coat on the surface to remove.

I did call Vans and that was their recommended fix. I asked if I should buff/polish the area once I was done and they said don’t bother just keep it dry. It does look very scuffed up compared to the rest of my shiny pieces but being that I’m probably going to paint the plane at the end of all of this I guess it doesn’t matter.

Btw I just looked at your second pic and realize that you have some work to do.
RV-7A builder
A320 Capt at some airline
Piper Warrior
2022 donator
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Old 06-22-2021, 10:28 AM
bjdecker's Avatar
bjdecker bjdecker is offline
Join Date: Jun 2005
Location: Georgetown, TX
Posts: 1,046

It looks like Central Texas Funk from the water (lime scale).

If you're willing, spray a little 9% white vinegar on a small section and see if it doesn't come off...
Brian Decker
RV-7 (Flying)
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Old 06-23-2021, 02:27 PM
A1AVIATON47 A1AVIATON47 is offline
Join Date: Apr 2008
Location: DEWEY AZ
Posts: 260
Default remove corrosion

HI, The only way to remove all the corrosion is to use acid, called in the paint world metal conditioner, there is one for steel and one for alum.
There should be a paint store in your area that sells auto paint, you will find meal cond. There and a lot of free advice.
I would not use just scotch bright all your going to do is damage the alclad the corrosion will come back. You will have to repeat the metal cond. Again before you paint,
I worked on a paint crew for several years painting new 747ís 727ís ect. We did not scotch a whole 747 new alum , old alum with corrison dif. Story acft washed with strong soap , metal cond, , was again , dry good, etch primer , primer for type on paint used, top coat, depending on order clear coat,
Long story short, you need to remove the corrosion shown in the pictures its only going to get worse, hope this helps you.
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Old 06-25-2021, 04:59 PM
KAndrews KAndrews is offline
Join Date: Jul 2019
Location: Troy, Texas
Posts: 3
Default Thank you

Thank you for the wonderful advice! You all pretty much follow the same line of advice except whether or not to use the scotch brite pad. I received the following advice from Builder Support:

I would clean well with soap and water (DI water or distilled water would alleviate the high pH concern.) Following up with scotchbrite scuffing and alumiprep followed by a coat of self-etching primer should address any concerns.

They also sent the following document addressing corrosion:

As for replacing the skin, they thought it might be overkill.

Since it is a relatively small area (comparatively speaking) and since it will be an interior surface, I am inclined to try the scotch brite pad. I can appreciate that I would not want to do this on an exterior surface and also that a 747 has a huge area to clean, but I do want to make sure all hint of corrosion is removed. I may test out a small patch of alumiprep and not use the scotch brite pad. It will be a "play it by ear" kind of decision.

Either way, I will let you know how this turns out, especially for those who come after us.
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