Tank 'Leak' at Rivets

[Brian Vickers]

I have not painted my RV4 yet but had a similar experience on my aluminum speed boat. I repaired a damaged area (wife rammed the dock) on the boat by splicing in a new section. The splice was secured using a doubler plate behind. I used flush rivets from my RV4 project to fasten the whole assembly, just like our airplanes. Before painting with DP primer, I used PPG DX 533 aluminum cleaner. The paint supplier was sure that I did not allow enough time for the DX 533 to fully evaporate around the rivets. He claims this caused a bonding failure and resulting bubbles. My bubbles only show up when the sun beats down on the boat in the summer. Maybe your last solvent wipe-down was not quite evaporated before the primer went on? Now, when I solvent wipe a riveted area for painting, I hit it hard with compressed air to clear any solvent out of the cracks around the rivets. I believe the paint supplier was correct in his diagnosis of my particular paint bubble problem.
Sincerely, Brian Vickers, RV4-finishing

[az_gila]

Originally Posted by Brian Vickers

I have not painted my RV4 yet but had a similar experience on my aluminum speed boat. I repaired a damaged area (wife rammed the dock) on the boat by splicing in a new section. The splice was secured using a doubler plate behind. I used flush rivets from my RV4 project to fasten the whole assembly, just like our airplanes. Before painting with DP primer, I used PPG DX 533 aluminum cleaner. The paint supplier was sure that I did not allow enough time for the DX 533 to fully evaporate around the rivets. He claims this caused a bonding failure and resulting bubbles. My bubbles only show up when the sun beats down on the boat in the summer. Maybe your last solvent wipe-down was not quite evaporated before the primer went on? Now, when I solvent wipe a riveted area for painting, I hit it hard with compressed air to clear any solvent out of the cracks around the rivets. I believe the paint supplier was correct in his diagnosis of my particular paint bubble problem.
Sincerely, Brian Vickers, RV4-finishing

Brian... one of the reasons for the alodine step after acid etch (DX 533 is an acid, isn't it?) is to neutralize the acid....

[edit: confirmed, it is an acid etch/cleaner]

That's one of it's purposes in the MIL-Spec painting process..

Even PPG recommends a conversion coating (aka. alodine) for aluminum.

http://www.ppg.com/refinishftpsite/d...lTreatment.pdf

gil in Tucson

[Brian Vickers]

Gil,
Yes, DX 533 has phosphoric acid. I'm not sure of the amount in the blend of other contents (butoxy ethanol, ammonium bifuoride and polyethylene glycol octylphenyl ether). I don't use DX 533 any more and have ammended my paint and prep process. Good point though....

[Kahuna]

Originally Posted by az_gila

Interesting that the Sikkens primer is not an epoxy.

I think that I would want an epoxy as a first layer on my plane whatever paint system was in use.... which is the case with most modern aircraft paint systems.

Did you have a choice of primers with the Sikkens system?

Were some primers epoxies and some not?

Was this a auto paint system?

gil in Tucson

Sikkens makes only one primer for their system.
This is an auto based system. base coat / clear coat .