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Paint woes

RV10Rob

Well Known Member
I had my RV-10 painted 5 years ago, and today during preflight I saw this on the horizontal stab.

paint1.png


paint2.png


The paint was just "bubbled up"; I removed it to take a look underneath. Any ideas what caused this and what I should do about it? Thanks...

-Rob
 
I'd bet on filiform corrosion. If that's the case, you'd need to remove the paint from the area, remove the corrosion, treat the corrosion, and repaint.
 
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Paint Woes

Heartbreaking. What brand/kind of paint and primer was used? Was the surface Alumipreped and Alodined prior to primer?
 
Looks like corrosion/oxidation to me. Unless you treat with alodine or some other chemical conversion treatment, the first coat of paint needs to go on within about 2 hours of abrading or etching it. Aluminum begins to oxidize immediately after removing prior oxidation layer (unlike steel, with AL the oxidation layer substantially slows down further oxidation).

If oxidation (early oxidation is not visible) is left on the surface, it will slowly oxidize under the paint over time. The oxidation process produces some excess gasses that cause the paint to bubble after lifting.

All of those tiny bubbles in the paint near the large bubble are early oxidation. You can see those tiny bubbles in the paint film of your large lifted paint. That was how it started.

Larry
 
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Are we looking at primer or aluminum under the paint?
If Primer, it is probably an adhesion issue from some oil contamination. I see a lot of little bubbles in that area.

If aluminum, it looks like the etch didn't get fully rinsed/neutralized in that area. Is the aluminum powdery?
You're going to have to remove all paint from that area, mechanically remove the corrosion, and re-do the prep and painting process.

You can try to blend it in, but you will probably have to paint that whole side of the stab.

Sorry man. Sucks.
 
Not an expert but as I understand it if the paint isn't put on within the primer's specified adhesion period it may have not performed. For example, with my primer, you have to paint within 24 hours or re-prime.
 
Yes.
Looks like filiform corrosion.

Not likely the fault of the products used but the process used applying them.

It is typically caused by moisture entrapment under the primer/paint.

This is why many years ago I stopped using the traditional etch/alodyn treatment before paint. I am always under a time crunch and there is never enough time to let the parts dry thoroughly (it can take many days depending on the conditions).

Paint and primer needs to be removed in effected areas and the metal sanded completely clean before refinishing.
 
As mentioned, it all depends upon if we are looking at primer or aluminum under that paint. Was the plane painted for the first time, 5 years ago or is it a repaint?
If it's aluminum, you have a slightly bigger issue in that it's likely corrosion and you will need to completely remove it before proceeding with any repainting. If it's a primer to base or single coat issue you only need to remove that top layer, scuff the primer and blend in a new top coat.
One thing not mentioned that, as I understand it, could cause a primer to base/topcoat separation is what is known as solvent pop. The solvents in the primer, is not given enough time to evaporate can become trapped beneath the top coat, causing it to separate. May have been that way for some time and bubbled a little but didn't break up until now. Look around and see if you have any paint "bubbles" anywhere else. We'll keep our fingers crossed that you don't find any.
Other than that, without more information, any one of the replies could be correct.
 
Wow, thanks all for the quick replies. It was painted by GLO, but was flying unpainted for ~1.5 years before that. I'll take a more careful look and better pictures next time I'm at the airport. Though I'm not an expert, it doesn't look like corrosion to me, just scuffed (but may be wishful thinking). The green primer underneath the paint looks clean.

-Rob
 
In my experience, solvent pop appears the first time the paint is given a good soaking in the hot sun. The heat is what makes the trapped solvent expand and "pop."

Larry

As mentioned, it all depends upon if we are looking at primer or aluminum under that paint. Was the plane painted for the first time, 5 years ago or is it a repaint?
If it's aluminum, you have a slightly bigger issue in that it's likely corrosion and you will need to completely remove it before proceeding with any repainting. If it's a primer to base or single coat issue you only need to remove that top layer, scuff the primer and blend in a new top coat.
One thing not mentioned that, as I understand it, could cause a primer to base/topcoat separation is what is known as solvent pop. The solvents in the primer, is not given enough time to evaporate can become trapped beneath the top coat, causing it to separate. May have been that way for some time and bubbled a little but didn't break up until now. Look around and see if you have any paint "bubbles" anywhere else. We'll keep our fingers crossed that you don't find any.
Other than that, without more information, any one of the replies could be correct.
 
Yes.
Looks like filiform corrosion.


This is why many years ago I stopped using the traditional etch/alodyn treatment before paint. I am always under a time crunch and there is never enough time to let the parts dry thoroughly (it can take many days depending on the conditions).

What process do you use then? Also, if alodine is a couple of years old, is that a problem for paint adhesion?
 
What process do you use then? Also, if alodine is a couple of years old, is that a problem for paint adhesion?

I'll share my process. Scrub parts with Comet and green pad and rinse thoroughly. Blow water out of crevices and internal areas aggressively. Let dry 24 hours, preferably with sun. Sand entire surface area of part and blow off. Clean with solvent based wax and grease remover. If unable to spray first coat in 2 hours, hit entire part with maroon pad, then blow and clean. In addition to removing the oxidation, sanding provides a better mechanical bond for the primer.

I was able to prep two wings and paint in the same session. 3 years and no lifting or corrosion. I used an epoxy primer under a signle stage PU paint.

Larry
 
yep, primer didn't stick. no corrosion. goes to show that the primer application may be even more important than the paint.
 
Peeled more paint and took a closer look today. I really don't see any corrosion. It looks like an approximately 1.5" x 18" section wasn't prepared properly, so the primer didn't adhere properly (you can see clean green primer underneath the paint).

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(click here for full size)

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(click here for full size)

On Aluminum, corrosion is severe oxidation. light to moderate oxidation is not really visible. The fact that your paint bubbled points to oxidation, even if you can't see it. Poorly adhered paint or primer doesn't bubble. It may lose it's bond, but stays flat and the paint around it holds it down until a force is applied and it fractures. It breaks off flat.

When oxidation isn't removed prior to painting, the primer bonds to the oxidation layer, which has a very weak bond to the aluminum. Once oxidation is present, it continues slowly, even under the paint layer. I don't know the chemistry, but it doesn't seem to require contact with air. The process produces a gas during the conversion and that causes the bubbling, as the gas is trapped between the aluminum and the paint.

In your photo, you can see the bondo (pink stuff) does the same. It is well bonded to the paint, but was bonded to the oxidation layer and therefore weak and lifted as the oxidation continued. That ring around the bondo is probably a primer applied after the bondo and prior to the final primer. You can see your final layer of primer bonded strongly to it, but the bond to the aluminum was poor or less strong. If it was poor prep on the final primer application, only the final layer of primer would have lifted.

To be clear, the cause here IS poor prep, but didn't want anybody to think it was as simple and just not cleaning it properly. When dealing with aluminum, part of the prep is removing the oxidation layer, which is difficult for some, as it is not visible like rust on steel.

Larry
 
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goes to show that the primer application may be even more important than the paint.

Most painters would tell you that the prep prior to the primer application is by far the most critical stage in a paint job and what causes most failed paint jobs. This is why good painters won't spray unless they do the prep.

Larry
 
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