Undercoating, Grey or Black?

[Gearbox]

Redoing the under carrage on my 1971 911S. Anyone know if the original under coating was actually Grey or Black? I know the tank was orginally Grey but the bottom turned black from years of road dirt. Or did it? Thanks Allan

[LKreg]

I will be interested to see the expert advice you receive on this question. When I stripped my 1970S down to the bare metal I asked the same question and got a lot of conflicting advice from an assortment of very knowledgable enthusiasts. Finally went with gray.

[pu911rsr]

What is the appropriate product regardless of color, they early stuff is really brittle and stiff compared to later undercoating.
Phil

[Scott Clarke]

Allan-
The undercoating in the engine and luggage compartments of my '70E Karman coupe were grey. I got a good, long look at that grey in the dozens of hours it took to remove it! I can't speak to the underside of the car, as I have not dug into it.
-Scott

[Gearbox]

What is the appropriate product regardless of color, they early stuff is really brittle and stiff compared to later undercoating.
Phil

I believe Porsche used the Wurth undercoating product that is sprayed on with a heavy finish. I found many suppliers of the product, but the gun is out of stock at each one. I ended up finding a German product called GravTex at my local auto paint store. The gun was only 20 bucks and the product is about 10 bucks a bottle (much cheaper). I used two bottles on the refinished gas tank in grey (I built it up heavy to match the finish of the Wurth product). There is no mixing and product dries hard over night and is paintable like the Wurth product. Very acceptable substitution. As for the "brittle-ness" early versus late, I think it was the same stuff, just aged more, or perhaps an improvement in the product to stay pliable longer. Seems that the undercoating on my '71 was brittle below the rockers and still was rubbery on the floor pans.