National Aeronca Association Bulletin Board

what exactly is zinc chromate and what are the differences between regular etching primer. also why do i see some wing ribs left bare aluminum and some painted. ive seen some green and some white? and where do i buy it. is it available in a spray can?

jsf74 wrote:what exactly is zinc chromate and what are the differences between regular etching primer. also why do i see some wing ribs left bare aluminum and some painted. ive seen some green and some white? and where do i buy it. is it available in a spray can?

Zinc Chromate is an excellent corrosion preventative, but is not the best primer if you are going to paint over it because it doesn't stick that aggressively. It comes in spray cans plus in bulk liquid.

Etch primers are good if you're going to paint over them, but most don't have the corrosion preventative properties of Zinc Chromate. Self Etching primers come in rattle cans and in bulk.

Both Zinc Chromate and Self Etching primers are subject to damage by the chemicals in most modern covering systems.

Epoxy primers are great corrosion barriers as long as you start with clean, corrosion free metal. They are chemically tough and won't be damaged by the chemicals in covering systems.

All primers add weight.

On my restoration, I'll be alodining the ribs, which is another way to add a corrosion barrier, but without the weight. Alodine is a chemical conversion process which makes the surface of the aluminum chemically inert. Chemicals will not harm alodine.

As to why you often see bare aluminum ribs. The alloys we use have a very thin coat of pure aluminum on their surface - the Alclad layer. Pure aluminum is extremely corrosion resistant, so (arguably) you don't need more corrosion prevention than the alclad layer. Based on the ribs in my 60+ year old wings, I'd say ribs are more likely to wear out or be damaged to the point of being unrepairable than they are to corrode away.

Bullseye! What Kyle said.

nkh

well that explains that. thanks.