Topic: What finish for underside stoneguard - 67 SJ

[Fastback2013]

Hello,

I have searched but could not find what the factory look would be for the underside of the stoneguard?
Would it be light grey with overspray of body color?
Or entirely body color?
In attachment a picture of my stoneguard, and looking at the positions where the fixation bolts sat it suggest body color?
Or red oxide (like backside of front valance) with body color overspray?
Thanks for clearing this out.
Have all a nice weekend,
Kind regards,
Jeroen

[J_Speegle]

Body color direct and overspray over red oxide. Different red oxide color/tint from your undercarriage or (for examples) fenders possibly.

The way the part is formed will guide you to how much and where direct spray and where more of an overspray surface will be.. Example for this part would be the face (forward) once the part is installed)


Since they would want to make sure this area was well covered with body color so as it was sprayed the area behind it would get direct or heavy overspray typically though the bent down or backwards edge would produce a shadow leaving mostly red oxide visible directly below and behind for a short distance, at the bend/form. So basically you can find nice coats of body color on the back side with thinner paint in the shadows to fine mist across the rear side with slightly stronger in areas directly behind focus sections. What you don't want is a nice coat of body color on exterior surfaces and a nice red oxide on the back side with no overspray - of a great noticeable difference between the two surfaces that catches the eye

[Fastback2013]

Thanks, Jeff!
Greatly appreciated!
The last part, I fully understand :

What you don't want is a nice coat of body color on exterior surfaces and a nice red oxide on the back side with no overspray - of a great noticeable difference between the two surfaces that catches the eye

Since the stoneguard is a long, small piece , would it be hanged vertically for painting?
or rather held horizontally?
I do not know enough about spray patterns, but it must make any difference, I assume ?
Thanks again for your time and effort!
Kind regards,
Jeroen

[J_Speegle]

The last part, I fully understand :Since the stoneguard is a long, small piece , would it be hanged vertically for painting?
or rather held horizontally?

Don't know. Never seen a shadow from the hook nor a run that would indicate a direction it was hung. Believe it was hung since that would match what we find in pictures and reduces handling of prepaint and post paint parts plus keeps them organized

I do not know enough about spray patterns, but it must make any difference, I assume ?

We would also have to take in account of the painters height, right/left hand, orientation of the part to the spray line and other factors but that is why we look for something in a range rather than a specific pattern on every one.

Here is a picture of a 70 upper valance to show how shadows were produced on the back side from the forward lip on that part.  The non-painted section has rusted where the red oxide was while where there is no shadow some body color can bee found. The rear edge was a sharp edge and did not face the exterior so there was not great effort made to paint that edge and due to this no overspray/direct application can be seen like from the front formed edge

[Fastback2013]

By all means, very interesting!!
Thanks Jeff!!
Totally agree that it is quite impossible (for the most of us  = hobbyists that restoring there car), that we can duplicate a correct estimation of left/right handed painter or at which height the piece was held, etc...
But you're totally wright about your explanation.
Thanks for adding that picture, it gives us a good visual taught of what you explained!

The unpainted section has rusted where the red oxide was 

Since my stoneguard was heavily rusted (see my added picture at the beginning) at the underside, is it a correct assumption that the red oxide was less durable than the actual (body color) paint?
Or am I totally wrong?
Or said in a different way : is the red oxide not the same 'quality' in comparison to paint?
Do not want to mix different items, but just saw the question from 'cmfuser01' concerning the finish of the inner fenders.
The pictures that you posted are very similar with the finish of my fenders, and where the rust (now) is, was there once the red oxide?
Just added/asked this for better comprehension, that's all 
Again, many thanks for your helping answers!
Kind regards,
Jeroen

[Bob Gaines]

Maybe someone can confirm or dispel but I was always under the impression that moisture can migrate somewhat through unprotected primer to the metal underneath. The paint on the other hand not so much. That also may explain why the rust is where the primer was opposed to the area with more paint overspray.

[J_Speegle]

Thanks for adding that picture, it gives us a good visual taught of what you explained!Since my stoneguard was heavily rusted (see my added picture at the beginning) at the underside, is it a correct assumption that the red oxide was less durable than the actual (body color) paint?
Or am I totally wrong?
Or said in a different way : is the red oxide not the same 'quality' in comparison to paint?

Believe that you have the evidence that the red oxide didn't hold up as well as the exterior paint over the factory primer. Remember that the red oxide that was applied to the floor of these cars for example

Yes all the bolt on parts that were assembled at other plants and shipped in were prepped and protected during shipping to the car assembly plants

[J_Speegle]

Maybe someone can confirm or dispel but I was always under the impression that moisture can migrate somewhat through unprotected primer to the metal underneath. The paint on the other hand not so much. That also may explain why the rust is where the primer was opposed to the area with more paint overspray.

Believe it depends on the type of primer. Straight old time primer does not seal out moisture and was designed (just my understanding) to improve the bonding of the top coat and the base providing short term protection over bare steel in this example. Primer sealer provide an improved bonding ability and had a barrier of sorts between the base and top coat . There was a period of time when locals would paint their cars with colored primer sealers then buff them to a shine locally. Think in general primer was a cheaper product than primer sealers but not by allot   

Epoxy primer sealers of the period were the next step up and protected the surface metal, helped bonding of the base and top coat but was more expensive and had other restrictive properties

Just my understanding from what was explained to me and experience as well as examples seem to support this but sure there is a greater and much deeper explanation

[Hipo giddyup]

Not sure how much was changed in assembly line practices, but for 65' they look to have been sprayed horizontally.

[Fastback2013]

Thank you all for the highly appreciated explanations and provided pictures!
As always, I have learned a lot 
Kind regards,
Jeroen

[J_Speegle]

Not sure how much was changed in assembly line practices, but for 65' they look to have been sprayed horizontally.

Not sure either - different year and plant so no telling