So cleaning up the bottom of the car to assess the entire car, and found this material that looks like a light coat of primer. It has enough grime on it to be original.
My question to anyone that was around when these were coming out of the dealerships is; what is it, and what was it supposed to do? There is no rust so it certainly worked, but this was a Nevada car all its life.

Mr Mayer perhaps you have an idea?

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It is PVC. That's what the factory was using to seal the cars with.

To my understanding, the underside of the car was a rust preventative undercoat that everyone says is grayish PVC.

What are you using to remove the black undercoat that is over the PVC?

Hey Mark -

I have to disagree with my esteemed fellow members on this, after both having been around back then (as was Mark/914sixer), & renewed research in recent years for my own 73's resto.

The factory undercoating was similar to what was used on the valances & rockers panels (& on the black painted 73-74 steel bumpers), a heavy eggshell texture, which was then painted over in body color on the underbelly & wheel wells, & black at the rockers/valances/bumpers.

The black spray-on coatings at the belly & wheel wells was a dealer applied "rust proofing" of varying reliability, & went by Zybart & a few other brand names (Zybart also had the drill-n-fill rustproofing too).

Dealers would often do the spray coating on most/all cars without buyer request because it was quick & east to spray it on & most dealers had franchises with the suppliers, so that they could charge for it with 40-60% profit margin, but usually left the drill-n-fill to customer request because it was very time consuming & more expensive to do it. The black spray was basically like today's formulatiuons for the semi-rubbery rattle can & roll-on/spray-on underbody coating & bed-liners.

My 73 914-2.0 had it put on before the original owner whom I bought it from even got the car, as well as having had 2 prior topside resprays from the factory L80E Light Ivory, first to Sahara Beige (like Steve's/smg - which the owner & I were unaware until I stripped some areas), then to the 72 Gold metallic when they & I bought it (OO only knew of the gold respray, but white was/is clearly visible on floor pans, etc.) - probably to try to sell it in better non-white colors. I always liked the "black-out" look in the wheel wells.

It did protect my underside from rust here in SoCal, & 72-76 were what's now known as El Nino years too, & several while it was my & the OO's DD up to May 85. The underside rust which did form was due to window washer bottle & M/C leaks into the front trunk wells, & rusting from the inside down.

You may recall the pix posted by Tod914 stripping the black coating off of his pristine Bahia 73-2L, & of Steve/smg stripping it off of his Sahara Beige when he got it. I think that their posts had some product(s), procedures & methods advice on how to clean it off best, & with least underlying paint damage. So I'd suggest a google search to read up more there.

PS - To clarify - the gray stuff looks like it could be the body color paint worn off of the factory undercoating, but I was answering you about your question on the black stuff, which lies on top of the paint, then factory undercoating.

Have Fun!
Tom
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This is not undercoating, it's a coat of grayish PVC. My '70 /4 has it.

Just going to leave this here ...

So is it still available to apply for the concours guy or what is the a modern equivalent?

Thanks Andy,
Definitely has a different texture. It doesn't seen to be a faded paint underneath, as its pretty uniform. My inpression is that it may have the PVC base coat, but also has a coating over the paint. I did try removing it in a small section and was able to het more color to show with a solvent. Mt search now is for the original material it was coared with on tbe outside.