When a car was travelling on the line, I understand that the primer was shot up towards the entire bottom, did it not keep applying that same primer right to the front crossmember?
From what I’ve been reading it sounds like it stopped spraying in around the firewall area.
The car/unibody was traveling in the direction so that the front of the body entered first so the floor application started at approximately the bottom of the firewall
This produced allot of runs and drips in an effort to cover as much as possible. Vertical surfaces were sometimes thin or nothing more than a mist because of the angle. Also, the jets stopped spraying before they reached the very back of the rear. Just forward of the rear cross member. All of this was to eliminate the raining down of paint and overspray on the car being coated and the car following. Some times a single or multiple jets clogged producing a strip of unpainted floor for a foot or the whole length of the floor. Not common at all IME but did happen. Have seen examples (other plants and years) where it was recoated by hand or not caught by any of the inspectors
If so was the next area up to the front crossmember hand sprayed?
After the rear 2/3rds of the floor area was painted the front frame sections and inner fender panels were coated by hand so that the spray could be controlled. If they had used the under-car spray system from the front cross member rearward all of the jets mounted in the middle and outer edges would have "thrown" their paint upward and not hitting any panels would have rained down everywhere creating a mess to fix and clean up
By applying the hand applied spray second it allowed the painters to cover over the earlier coating of the floor and reduce the chances of leaving a gap between the two applications which would rust quickly in most regions
As a mention the products used were not what most people thing of when they think "primer" so using the term is misleading. Primer is an open surface that promotes attachment of following coats and applications of other produces. They will allow rust to start. Instead a primer sealer was used at some plants that was epoxy based which produces a low to higher gloss finish. For this year and plant a epoxy primer sealer was applied or a base with left over paint from either the last shift or when ever the workers collected the near empty drums and poured the remains into the vats to create a combination that would be used during those production periods
The source that supplied paint/primer sealer to the floor jets was a different source than the one that supplied the hand applied application for the firewall forward.