It's my understanding that a lot the island hoping durning the war was on dirt runways.

Hi ,

You have to consider the grade of aluminum used at the time period .
During WWII , aluminum wasn't up to the quality of today's standards and oxidation was a key factor , causing a lot of paint lifting . I think galvanic corrosion played a part in paint chipping , as well . I'm no painting expert , so this is a guess , but might explain why U.S. A/C used a zinc chromate for a primer coat (?)
As in our hobby , weight was a crucial factor and life expectancy of the aircraft wasn't ... well let's say extremely long , so some counties had different ideas on how much to paint .
Most Luftwaffe A/C had at least five coats of "Flieglac" (lacquer) to keep oxidation at bay (not sure about IJN or IJA A/C).
As previously mentioned , tropical conditions and dirt fields , had a lot to do with paint demise .

Hope this helps a bit ?

Rob Killick

Hi ,

You have to consider the grade of aluminum used at the time period .
During WWII , aluminum wasn't up to the quality of today's standards and oxidation was a key factor , causing a lot of paint lifting . I think galvanic corrosion played a part in paint chipping , as well . I'm no painting expert , so this is a guess , but might explain why U.S. A/C used a zinc chromate for a primer coat (?)
As in our hobby , weight was a crucial factor and life expectancy of the aircraft wasn't ... well let's say extremely long , so some counties had different ideas on how much to paint .
Most Luftwaffe A/C had at least five coats of "Flieglac" (lacquer) to keep oxidation at bay (not sure about IJN or IJA A/C).
As previously mentioned , tropical conditions and dirt fields , had a lot to do with paint demise .

Hope this helps a bit ?

Rob Killick

Hi Rob,

The aluminum used in American airplanes was good even back in WW2.  The aluminum used in Japanese airplanes varied.  Aluminum used by American, Japanese, & Germans in airplanes for structural purposes was mostly 2024 alloy and 7075 alloy.  These alloys had copper and zinc plus other alloying materials in them which could, if not properly kept in solution, cause rapid corrosion.  Proper heat-treating was the key to keeping the alloying elements in solution, and if not correctly done intergranular corrosion was the result. 

2024-T3 sheets were typically used in aircraft stressed skin construction, and because of the low corrosion resistance of bare 2024 it is almost always coated with pure aluminum and called "Alclad".

7075-T6 & 7075-T651 were typically used for spars and other highly stressed members and because when used for spars it was installed bare (no alclad), they were particularly subject to intergranular corrosion if not very carefully heat-treated.  The Japanese were having great difficulty with their manufacturing processes, particularly after the B-29s arrived over their homeland, so their heat-treating processes suffered greatly.  A few years ago Planes of Fame here in Chino, CA had an A6M5 Zero (in addition to the one that they still have and fly) and it had intergranular corrosion of the main wing spars that was so bad the spars had swelled up to over an inch above the wing skins.  This one was cosmetically treated, painted, and sold to Japan as a static display.  The remaining A6M5 that is flying here in Chino also had serious intergranular corrosion of the spars but they had new spars machined out of *American* 7075-T651 and it is holding up great.

The primer used during WW2 was a zinc chromate enamel or lacquer base paint which did two things: 1) provided adhesion for the topcoat paint and 2) provided corrosion protection against electrolytic corrosion.  The type of corrosion that the primer protected against is filiform corrosion which is on the surface of the aluminum.  Since filiform corrosion mostly happens under paint then the primer is necessary.  These days we use epoxy primer with strontium chromate pigment as an improved paint base and corrosion protection.

Galvanic corrosion didn't play as much of a part in paint chipping as did not adequately cleaning the surfaces to be painted at all stages of the paint job from the bare aluminum skin all the way through the topcoat colors.  Field repairs both by Japanese and Americans were done under tough conditions so paint jobs suffered.  Also, both sides flew through rain and hail so chipping was common.

Just as a note, the most accurate representation of combat servicable WW2 airplanes that had had paint repaired in the field is Ron Burns' series of C/L stunt warbirds. 

The fact is not much stuck well to aluminum. When I was in the Air Force crewing F-106s, they were painted with lacquer and even a new paint job would tend to peal and chip within weeks of it being finished. During that time, polyurethanes were starting to be used and as our Sixes went to Depot for thier majors, they were being painted with poly, It was high gloss and tuff as nails but still, there was a tendancy for chips to propagate at high maintanence areas like the lower engine bay panels that were opened at every shutdown. Today while paints are much better then they used to be, aluminum is still not the best material to gat paint to stick to.

By the way, if you want to see some really rough US warbirds, watch "Thirty Seconds over Tokyo", there are some of the roughest rattiest B-25's in that movie I've ever seen pictures of.

Hi Randy,

Actually, getting paint to stick to aluminum is more a matter of surface preparation than it is a material compatibility problem.  The bare aluminum skin has to be first washed with a soap solution to remove the water soluble oils and other contaminants, then acid washed, then treated with alodine.  Then immediately prior to priming it has to be water washed and allowed to dry.  The airplane should be in the spray booth as soon as possible after water washing, and should not be touched with anything like hands, rags that are not completely clean and new (no red shop towels...the worst), tack rag just before applying the epoxy chromate primer, then go ahead and prime.  The big problem that people have with painting aluminum is not getting and keeping the surface clean enough.  In my shop I have painted many WW2 and Korean era and one T-38 warbirds that have been flying for twenty years with little problem with chipping or peeling.

Ramp jobs are done all the time both by the Air Force and private individuals and for some good reasons; however it is just too difficult to control the cleanliness under those conditions to get the adhesion needed.