Corrosion treatment

[surfly]

I live in a highly corrosive coastal zone area and am considering using a light coat of zinc chromate on the interior of the wings, empennage, and flying surfaces before final riveting. Also using zinc chromate on the interior of the fuselage followed by a neutral color, possibly white. Exterior will be paint although I am considering a wrap instead.
Thoughts and/or suggestions?
Sherm 0176

[Gunther]

I'm doing something similar, Sherm. I put zinc chromate on both sides of all aluminum parts and sheeting. I apply with a light coat followed by a cross coat using marine quality spray bombs. I plan to finish the interior with upholstered side panels and neutral color, possibly grey or white. I'm not sure about exterior paint yet but I want to thoroughly investigate water-borne options.

An better protection would be a two part epoxy-based zinc chromate, if it's still available. As far as I know, zinc chromate is one of the few primers that reduces oxidation by creating a small voltage.

Perhaps the ultimate option would be using a chromate conversion coating in an immersion bath process followed by spraying epoxy zinc chromate on both sides. I recall an RV builder talking about doing this in a forum a while back.

Cathodic protection may play a role some day as well.

Gunther

[Bryan Cotton]

ZnCr is best used after acid etch and alodine. Otherwise it seems like it does not adhere as well. I switched from ZnCr to SEM self-etching primer from a spray can which goes on hard and sticks well without the alodine. Epoxy is the best if you don't mind the hassle.

[SvingenB]

It's not really necessary. You can make boats for salt water operations out of 6061. I just use rattle can etch primer on all mating surfaces. Boats are normally welded, thus no mating surfaces. Blank sheets will not corrode in a million years. I have one test sample on my boat (salt water). It has been there for almost a year now, and no corrosion to the sheets.

But, there is one thing. The Sonex line of aircraft use stainless steel rivets. This is normally no problem, but when getting near salt (marine atmosphere), there will be galvanic corrosion of the aluminium that is in contact with the stainless steel. This is a common phenomenon in boating/sailing, and several products exist to prevent this. I use Duralac on all rivets. Duralac is a jointing compound made for boats and aviation.

So, my recipe (for what it's worth) is Duralac on all SS rivets and a primer on mating surfaces only.

http://www.llewellyn-ryland.co.uk/duralac.html

[XenosN42]

I considered finishing my OneX with wrap and spoke with a company that advertises on the internet. No need to give their name - if you're really interested in wrap it is better for you to do your own research of companies in your area. You may get a different response. Don't always believe the first thing you hear or read.

This company told me that they generally stay away from Sonex aircraft because of the high number of proud rivets. The time required to get the wrap to lay just right around the rivets just isn't worth it for them. For my OneX they quoted an estimate of $6,500, and that is above my budget.

-- Michael
N42XE - XENOS - flying 4 years
N169XE - OneX - first flight within 2 months

[ededoad]

I live in Corpus Christi and I have primed most the interior . Some items I did not, I was thinking thinking of the boats that are made of 6061. These boats last for several years but not as long as the plastic ones in a saltwater environment. I left a small piece of angle on my covered patio for several months . The upward side was corroded beyond the point where it could be salvaged. The downward side was just fine. If you live in a coastal area interior priming is a must unless you store the aircraft well inland and in a hangar.

[mike20sm]

I just got a pic from my dad in the winter storm that's hitting the Carolina's. After attending the Sonex Workshop Instead of building a lamp out of the wing piece, I didn't want to be hassled with getting it back home so I told my dad to expose it to the elements so I can monitor any corrosion that might occur until it come time to build my wing. I've since told him to put it on it's side so the elements can get in the nooks and crannies.

[samiam]

Ahh, the primer debate. I do not live near the coast, and am not priming anything. It feels so good to have moved to the dark side. :)

[fastj22]

Nor do I live near the coast. Just finished up my condition inspection after 3 years flying, zero corrosion. I had a 1966 C150 too, never had any corrosion. They don't primer the insides of them either.

Now I did primer the inside of my cockpit. Just because I liked to dull green look.

[13brv3]

After a few RVs, where you're considered the lowest form of life if you don't spend more time priming than building, the Onex kit is a pure joy! I feel like I'm cheating by not priming :-)

Cheers,
Rusty