Paint & Corrision

[Aussieflyer]

My RV14 is six years old. A recent close inspection reveals small patches of worm corrosion at about thirty locations. The corrosion was present mainly at the lap joints and trailing end of flight surfaces.
My paint shop told me that RV's at about 5 or 6 years old start showing signs of worm corrosion.

It has been suggested that the aluminum used by Vans may have gone through a bad patch. I'm not convinced but I thought I'd ask is anyone else suffering corrosion at 5 years old?

I spoke to one respected aircraft painter today and he told me that automotive paints shops fail to seal the lap joins and he is repairing many automotive painters work at 5 to 6 years.

Is anyone else experiencing worm corrosion at 5 to 6 years?

 

[chaskuss]

"Worm" corrosion as you call it, is correctly called filliform corrosion. There are 8 different types of corrosion. Filliform corrosion is one of the 4 types that applying Alodine prevents. Sounds like this may be caused by poor paint prep. Was your painter an aviation or car painter?

https://www.corrosionclinic.com/types_of_corrosion/filiform_corrosion_underfilm_corrosion.htm

Considering where you live, the salt air environment is the most likely cause of your issue. Builders living/flying in warm coastal areas should strongly consider Chromic acid conversion [aka Alodine, Iridite, etc] and Mil Spec epoxy primer for corrosion protection during assembly. The Mil Spec epoxy primer protects against 6 types of corrosion and the Alodine protects against 4. Between them, they offer protection against all types of corrosion.

 

[Richard Connell]

Pretty much every middle aged RV I know of here (coastal) has filliform signs somewhere on the airframe where skins overlap externally.
I suspect either lack of alodining and/or priming pre assembly on overlapping skins or perhaps insufficient drying of seams post rinse and painting.

 

[rvbuilder2002]

or perhaps insufficient drying of seams post rinse and painting.

This is the predominant cause of this type of corrosion

Your painter is trying to pass the buck, but it was likely caused by their painting processes. Most predominantly from using water during the cleaning process and then not waiting long enough before the painting process was started.

 

[JonJay]

I have some here and there, almost from day one. Not at the seams, just randomly. A few years ago I found an obscure area under the HS and slowly removed the paint to see how deep the corrosion might be. To my surprise, what appears to be corrosion of the aluminum wasn’t. The “worm” like “corrosion” wasn’t in the primer layer, only the top coat, or between the top coat and primer. I left this area untouched as bare metal. It’s been years and I inspect this area all the time. It’s stayed perfectly clean.
I have asked here before but nobody had a theory.

So, is it really corrosion you’re seeing or some type of paint anomaly like mine.

 

[swisseagle]

All painters are extremely focused on the surfaces so that everything always shines and no run or other imperfections are.

As a result, the edges and corners are often neglected, both during preparation and during painting.

An Alclad sheet never starts to corrode in the middle, but where it has an edge, i.e. where there is no pure aluminum (Alclad) that protects, where there is corrosive alloy.
There it will start.

May be a good idea to at least prime the lap joints before they get riveted.