Navy aircraft exterior primer question...

tommieboy

tommieboy

SOH-CM-2025
Not sure if this is the proper forum, but here goes....

I'm working on a weather beaten repaint for Virtavia's Convair RY3 Tradewind flying boat, and would like to know if anyone happens to know what color primer was used on the exterior of hull.

Thanks in advance.

Tommy
 
tommieboy said:
Not sure if this is the proper forum, but here goes....

I'm working on a weather beaten repaint for Virtavia's Convair RY3 Tradewind flying boat, and would like to know if anyone happens to know what color primer was used on the exterior of hull.

Thanks in advance.

Tommy
Click to expand...


Zinc chromate green?
 
Being a seaplane, I would expect that all of the skins were anodized, as was done by some other manufacturers of flying boats and Navy carrier-based aircraft (like Consolidated and General Motors). With anodized skins, any areas where the paint has come off would be silver. However, the combination of anodized skins and paint would be fairly bullet proof - all of the photos and video I've seen of R3Y Tradewinds show them to be in quite pristine looking condition.

I think the most pronounced effect of a weather beaten R3Y would be that its glossy sea blue paint finish would be faded (lighter) and flat, and blotchy, where the sun and rain hits the surface of the aircraft the most, like the top of the wings, top of the horizontal tail surfaces, and top of the fuselage, with a sort of 'gradient' effect down the side of the fuselage and other surfaces. Like these photos of the Collings Foundation B-24 show:

https://www.facebook.com/collings.f...0.1425938271./509726299089444/?type=3&theater
https://www.facebook.com/collings.f...0.1425938271./514478098614264/?type=3&theater
https://www.facebook.com/collings.f...0.1425938271./514472495281491/?type=3&theater
https://www.facebook.com/collings.f...0.1425938380./403755839686491/?type=3&theater

With regards to use of chromate zinc (being a treatment rather than a paint), the color of the finish depended on how many coats you used. Amongst all aircraft manufacturers, the general rule of thumb was that for aluminum surfaces, such as skins, that chromate zinc would be applied to, only one coat would be used - and a single coat results in a yellow finish. On other alloys, like magnesium parts, and especially where two different metals come into contact, two coats of chromate zinc would be applied on those parts - and two coats result in a green finish. This is why when you look into the interior confines of vintage military aircraft, there is usually a mix of yellow and green primer finishes throughout - there really was a method to the madness!
 
Bomber_12th said:
With anodized skins, any areas where the paint has come off would be silver. However, the combination of anodized skins and paint would be fairly bullet proof - all of the photos and video I've seen of R3Y Tradewinds show them to be in quite pristine looking condition.
Click to expand...

Just to clarify, would they still use a primer over the anodized skin as part of the paint system?

Tommy
 
Bomber_12th said:
Being a seaplane, I would expect that all of the skins were anodized, as was done by some other manufacturers of flying boats and Navy carrier-based aircraft (like Consolidated and General Motors). With anodized skins, any areas where the paint has come off would be silver. However, the combination of anodized skins and paint would be fairly bullet proof - all of the photos and video I've seen of R3Y Tradewinds show them to be in quite pristine looking condition.

I think the most pronounced effect of a weather beaten R3Y would be that its glossy sea blue paint finish would be faded (lighter) and flat, and blotchy, where the sun and rain hits the surface of the aircraft the most, like the top of the wings, top of the horizontal tail surfaces, and top of the fuselage, with a sort of 'gradient' effect down the side of the fuselage and other surfaces. Like these photos of the Collings Foundation B-24 show:

https://www.facebook.com/collings.f...0.1425938271./509726299089444/?type=3&theater
https://www.facebook.com/collings.f...0.1425938271./514478098614264/?type=3&theater
https://www.facebook.com/collings.f...0.1425938271./514472495281491/?type=3&theater
https://www.facebook.com/collings.f...0.1425938380./403755839686491/?type=3&theater

With regards to use of chromate zinc (being a treatment rather than a paint), the color of the finish depended on how many coats you used. Amongst all aircraft manufacturers, the general rule of thumb was that for aluminum surfaces, such as skins, that chromate zinc would be applied to, only one coat would be used - and a single coat results in a yellow finish. On other alloys, like magnesium parts, and especially where two different metals come into contact, two coats of chromate zinc would be applied on those parts - and two coats result in a green finish. This is why when you look into the interior confines of vintage military aircraft, there is usually a mix of yellow and green primer finishes throughout - there really was a method to the madness!
Click to expand...

What an informative post! Thanks John. I now wish I was still making plastic models to put this to use. Well maybe after retirement, if that ever happens...
 
Bomber_12th said:
With regards to use of chromate zinc (being a treatment rather than a paint), the color of the finish depended on how many coats you used. Amongst all aircraft manufacturers, the general rule of thumb was that for aluminum surfaces, such as skins, that chromate zinc would be applied to, only one coat would be used - and a single coat results in a yellow finish. On other alloys, like magnesium parts, and especially where two different metals come into contact, two coats of chromate zinc would be applied on those parts - and two coats result in a green finish. This is why when you look into the interior confines of vintage military aircraft, there is usually a mix of yellow and green primer finishes throughout - there really was a method to the madness!
Click to expand...

That's not quite true, zinc chromate in its natural form is a coating, not a paint, it is mixed with paint bases to give the finishes that are seen.
Different paint manufacturers' had different mixes, so you can get zinc chromate primer in a variety of colours, and some of the colours seen in internal areas of aeroplanes are a finish coat applied over the primer.

(This will explain ---- > http://www.ipmsstockholm.org/magazine/2004/01/stuff_eng_interior_colours_us.htm )

Primer paint would indeed be used over anodised aluminium alloy, as the primer serves 2 basic functions, to protect the anodised layer and
give a base for the topcoat to bind to. (primer does have a few other things to do, but not really necessary in this discussion)

ttfn

Pete

(Licensed Aircraft Engineer, RAF ret'd)
 
I just wanted to explain, I admit in very simple form, why there were often both yellows and greens throughout the interior confines, as has been relayed to me from those who restore warbirds today to original/factory condition - it depending on what material it was that was being primered - and that there isn't such a thing as "yellow zinc chromate" or "green zinc chromate", despite the various applications being described as such. Raw zinc chromate will show-up yellow (with a slight green tint), and during WWII especially, one raw coat was usually all that was used for any aluminum parts/surfaces (though still, a lot of aluminum was left un-primered, as long as the clad finish remained intact). A single coat of raw zinc chromate can also look different between two different batches and between two different sheets of aluminum that it is applied to, if the finish on the aluminum is different between the two - one result may be slightly darker/greener than the other. Zinc chromate gets greener as more black pigment is added, such as used to identify two applications of zinc chromate, used on magnesium parts and castings ('interior green' paint was made the same way, by adding black pigment to zinc chromate (which also varied from one manufacturer to the next - there was no standard)). Grumman and General Motors actually used a gray primer during WWII, which no one else did, besides also using other zinc chromate-based primers. Brewster and Vought used zinc chromate mixed with red pigment, which created the 'salmon' color primer as seen on their aircraft. North American Aviation had, early on, some very dark zinc chromate finishes on dual-application parts, in which the shade was something like, or darker than, forest green.

I've seen a number of Grumman/General Motors WWII aircraft, in the process of being paint-stripped, down to their anodized skins, and there has never seemed to be any signs of primer on the exterior surfaces of the skins, only all throughout the interior.

(And this is all with regards to WWII-era mass manufacturing, and may not have much basis in similarities to post-WWII manufacturing.)
 
Boeing Primers

This may or may not be applicable to older paint formulas, as it is from the '90s, when I worked in final assembly in Renton (737 and 757 lines).

We were instructed that the "Green" primer was a general use primer, and the "Yellow" was to be used in areas with fuel exposure, as it was fuelproof. We also used a clear gloss urethane coat over part marks, I don't remember it's proper name, we called it "Finch". Finch was supposedly proofed against hydraulic fluid. If you needed to remove Finch for some reason, it took Methyl Propyl Ketone and 5 to 10 minutes of energetic scrubbing with a nylon bristle brush.

Likewise, there were different varieties of sealant, again seperated into general and fuel proof.

Steve (Former Bench Mechanic, Assembler-Installer and Sealer)
 
Bomber_12th said:
I just wanted to explain, I admit in very simple form, why there were often both yellows and greens throughout the interior confines, as has been relayed to me from those who restore warbirds today to original/factory condition - it all depending on what material it was that was being primered - and that there isn't such a thing as "yellow zinc chromate" or "green zinc chromate", despite the various applications being described as such. Raw zinc chromate will show-up yellow (with a slight green tint), and during WWII especially, one raw coat was usually all that was used for any aluminum parts/surfaces (though still, a lot of aluminum was left un-primered, as long as the clad finish remained intact). A single coat of raw zinc chromate can also look different between two different batches and between two different sheets of aluminum that it is applied to, if the finish on the aluminum is different between the two - one result may be slightly darker/greener than the other. Zinc chromate gets greener as more black pigment is added, such as used to identify two applications of zinc chromate, used on magnesium parts and castings ('interior green' paint was made the same way, by adding black pigment to zinc chromate (which also varied from one manufacturer to the next - there was no standard)). Grumman and General Motors actually used a gray primer during WWII, which no one else did, besides also using other zinc chromate-based primers. Brewster and Vought used zinc chromate mixed with red pigment, which created the 'salmon' color primer as seen on their aircraft.

I've seen a number of Grumman/General Motors WWII aircraft, in the process of being paint-stripped, down to their anodized skins, with no signs of primer on the exterior surfaces of the skins, only all throughout the interior.
Click to expand...

Indeed, before we too bogged down on minutae, back in WWII aeroplanes were being mass produced for the war effort, and paint was not exactly in
abundant supply at all times, and there were time pressures associated with completing the aeroplanes in as short a time possible, so if it didn't get primer what the heck, the life expectancy was only a few missions after all.

ttfn

Pete
 
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