Primer question?

[Charles in SC]

I am just curious, maybe my mind is working overtime. On the old military aircraft from ww2. The planes I see were painted with Zinc Chromate inside. Were they primed before assembly or after. A related question, if two parts are primed or painted before assembly there are two layers of paint between the two parts joined with rivets. It seems to me that the paint/primer is not as tough as bare metal would be and might loosen with age. Is there any merit to this or am I just being anal.

 

[Kyle Boatright]

I am just curious, maybe my mind is working overtime. On the old military aircraft from ww2. The planes I see were painted with Zinc Chromate inside. Were they primed before assembly or after. A related question, if two parts are primed or painted before assembly there are two layers of paint between the two parts joined with rivets. It seems to me that the paint/primer is not as tough as bare metal would be and might loosen with age. Is there any merit to this or am I just being anal.

On your first question, the parts were painted before assembly.

To answer your second question, as long as there is no relative motion in the joint (i.e. the parts are firmly joined), the primer between the parts will hold up for a long time.

 

[Transporter]

MIL-R-47196A

MILSPEC MIL-R-47196A covers riveting...and specifies priming:

"3.4.3 Repair limitations.
When the rivet material is dissimilar to the material being riveted (reference MIL-STD-171), the rivet hole, countersink, and rivet shall be coated with zinc chromate primer in accordance with TT-P-1757 prior to installation. The rivet shall be installed while the primer is in the wet condition.

3.5 Corrosion prevention.
Unless other finishing requirements are specified on the engineering drawing, surfaces which are painted, primed or chemically treated prior to riveting shall have the surfaces, including rivets finished in the same manner after riveting, per specifications applicable to the parent material. Any exterior damage to the finish of the parent material shall be touched up to the same requirements."

This is (not surprisingly) similar to WWII methods...

MIke