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Gas tank coating

So I recently tinted some U-pol Gravatex to match the original Wurth shutz. Unfortunately, when stripping my gas tank I didn't think far enough ahead to save some of the gas tank coating so I could match the color. I have attempted to find reasonable representations on the internet but the lighting from picture to picture can make the same tank look light grey in one photo to nearly brown in another. The photos below are from another Pelican's thread. The photos are all from the same tank and it appears to be the tanks original coating. As you can tell the lighting makes the color vary. I think the last photo is close but I am not sure.









Can anyone provide any insight? How close in color is the tank coating to the undercoating?
Old 01-12-2017, 07:05 PM
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What kind of car is it? Year?
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Old 01-12-2017, 07:23 PM
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The color of the tank in my SC is closer to the second to last photo. More tan than grey.

This weekend I can photograph it with a DSLR, shot in Raw so I can make sure the white balance is correct.

Mark
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Old 01-12-2017, 08:56 PM
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Dave- It is a 74 911

Mark- That would be great. Thank you.
Old 01-13-2017, 02:20 AM
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A couple observations...

I don't think Wurth made the original material, for what it's worth. There has been a discussion about who made it but I can't remember the details. People use Wurth because it is readily available and a good product.

I think this material changes color, with time. My opinion is that it is originally gray and turns warmer, even brown-ish, with exposure to all sorts of things. Even contact or proximity to a tire changes the color. Obviously, glues, fuel vapors and other things can change it.

Attached is a photo of a tank in a low mileage '72 that I used to own. It was driven for a few years, then parked for decades, in a dark storage facility. You can see the discoloration in areas where proximity to something changed the color from the original gray to brown. Note, also, the bleaching around the fuel sending unit. From fuel vapors? I'm fairly sure that a '74 would have had the same coating.

JR

Old 01-13-2017, 06:50 AM
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Here's a tank from an equally low mileage '80 930. Note the areas that have turned brown. The brown area on the far right is actually glue overspray.
Old 01-13-2017, 06:55 AM
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Here's a shot from an '86 930. Notice the horizontal surfaces have started to turn a warmer color, in varying degrees, but the vertical surfaces are still a fairly cool gray.

This series of photos also shows that the material was fairly consistent over the years but the application varied quite a bit, probably from different people holding the spray gun.

Old 01-13-2017, 07:00 AM
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Just repainted mine couple of weeks ago. Med.Grey Flexable bumper spray.

Last edited by 911 SLANT; 01-13-2017 at 02:08 PM..
Old 01-13-2017, 09:39 AM
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I've researched tank painting threads, and its interesting that I hadn't seen anyone mention the possibility that the color of the tank changed with age. Makes sense though, since I see a lot of photos of light brown tanks, but everyone seems to consider some shade of gray as correct.

My car is far from original, so I plan to go with Rustoleum Smoke Gray, which seems to be a popular (and inexpensive) choice.

Mark
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Old 01-13-2017, 10:15 AM
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Thanks for the info Javadog, It is my understanding that U-pol supplied the shutz, SKS to Wurth. I would agree the coating either changes color or is susceptible to staining over time. I came to that same conclusion with the undercoating. My opinion is it stains vs. changes color. When I removed the shutz from my wheel well the outer layer was far darker in color then the side against the sheet metal. In addition when I scrapped the surface of the shutz that was closest to the body the layer under neither was lighter still.

You can see what I am talking about on the paint and body work forum, I started a thread called shutz color match. There are some photos.

I know I am not going to match exactly just trying to get close.

Thanks again for everyones help and input. Keep it coming.
Old 01-13-2017, 12:21 PM
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I think you'll find that most products like this will dry to a darker color on the exterior skin than what you'll observe by cutting into it. I think the color is relatively stable unless it is exposed to liquids or fumes. I think there was very little beige to it. I'm not even sure I'd call it a very warm gray.

JR
Old 01-13-2017, 12:56 PM
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No, the last photo is primer. The tank does not look silver/grey like that. Is it more of the cream yellow parchment you see in the other photos.
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Old 01-13-2017, 01:20 PM
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Quote:
Originally Posted by javadog View Post
I think you'll find that most products like this will dry to a darker color on the exterior skin than what you'll observe by cutting into it. I think the color is relatively stable unless it is exposed to liquids or fumes. I think there was very little beige to it. I'm not even sure I'd call it a very warm gray.

JR
I would agree it may dry darker but not that dark. The skin is clearly stained form years of road grime.

The original photos I post of the tank above I think indicate that. The last photo appears to be after the tank was washed.
Old 01-13-2017, 01:31 PM
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I wasn't trying to suggest you should use the color of the undercoating in your wheel wells. That won't even be close to the right color. All I was saying was you might want to make it a little darker than the color yhat you see when you are scraping off the undercoating and are looking at the color on the back side.

The photos of the tank you posted show a tank that is far from the original color. Look at the photos I posted and select a gray that matches the grayest, least beige, areas in my photos.
Old 01-13-2017, 01:38 PM
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Definitely not primer
Old 01-13-2017, 02:10 PM
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I had to replace the tank on my low mileage '88 because it sat in a garage so long it developed rust on the interior. I can scrape some of the coating off the tank and send it to you if you want. I remember taking some coating to the hardware store to get a good color match for the new tank.
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Old 01-14-2017, 03:13 AM
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I cleaned and scraped a piece of paint/undercoating crap off my old damaged '86 tank, got paint matched at local paint store. New donor tank was rattle can sprayed with Wurth paintable undercoating (black) to match texture of the '86 and then hand painted, yep, hand painted. Dare anybody to find any brush marks.



Cheers,
Johan
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Old 01-14-2017, 04:31 AM
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Quote:
Originally Posted by javadog View Post
Here's a shot from an '86 930. Notice the horizontal surfaces have started to turn a warmer color, in varying degrees, but the vertical surfaces are still a fairly cool gray.

This series of photos also shows that the material was fairly consistent over the years but the application varied quite a bit, probably from different people holding the spray gun.
This is an issue that seems to get rehashed over and over.. really not sure why?

As Javadog stated and has shown, the tanks were grey when new (they have never been brown or tan) and tend to discolor over time and turn the kinda warm brown in color.. I would suspect from fumes, heat, outgassing etc.. The prime example around the circle area of the tank would be the spare tire.. it's pretty widely known that they leach brown over time. I seen this in other cars as well where the actual body-color paint in the spare tire well is kinda brownish around the spare.

Again, as Javadog states, there are noticeable differences in the application of these products during production over the years, weeks or even days! Don't forget, these cars were pretty much hand built up through the mid nineties. As far as the 60's 70's & 80's cars.. just look at some of the production line videos. So if Hans had a rough night, or was having a bad day.. whatta ya think his production looked like? There are areas of your 911 where the undercoat/shutz was slathered on with a brush prior to the tub being painted, look at the weld spatter and the difference from weld to weld on your frame rail in your trunk.. its all factory and it ain't perfect.

However, there are so many newbs to Porsche culture now, and they all want to make or debate how perfect these cars are/were.. their not!

I'm just say'n..


Quote:
Originally Posted by drcoastline View Post
Thanks for the info Javadog, It is my understanding that U-pol supplied the shutz, SKS to Wurth. I would agree the coating either changes color or is susceptible to staining over time. .

I know I am not going to match exactly just trying to get close.

Thanks again for everyones help and input. Keep it coming.
I'm not so sure that U-pol supplied the shutz, SKS to Wurth. Both are world-wide chemical companies one being based in England and the other in Germany. Although, we all know that the grey SKS is no longer available but the U-pol is a pretty good match if not spot on.. so maybe?
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Old 01-14-2017, 06:17 AM
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I agree with Javadog and Onboost. The original gray aged over time for various reasons to the tanish colors pictured above.

My exposed sections of my 73 tank looked exactly like the first two pictures in this thread before stripped and re-coated it. The rear of the tank, above the outlets and below the seem was still pure gray. No light gets in there, so I think that a lot of the color change is from UV, and maybe out gassing from the spare tire.

Before I stripped the tank(about 10 years ago), I cut a sample square from the back side, sealed it in a zip lock bag, and stuck it in a drawer. I haven't seen it since. I'll try to find it and post a picture here.

At the time, the 'fashionable' replacement coating was gray water based Wurth SKS Stone Guard, applied with a shutz gun (not the rattle can version). That is what is pictured below. It was a close but not perfect color match to that original patch from the back of the tank.

However, the final cured characteristics of the SKS Stone guard are much different from the original material. The original was rubbery, where the water based SKS cures rock hard. More importantly, the SKS has no resistance to solvent damage at all. Even a minor fuel spill will turn it to liquid instantly.

I found out about the chemical sensitivity after the fact, so my tank is un-coated, and I've saved enough of the SKS for minor touch up. The next time it is out of the car I'm going to clear coat it.

The good news is that this makes the current non-availability of the gray color irrelevant, and I wouldn't use it again anyway, because of the brittle texture.

If I were doing this again, I would use Uon's method. Use any rubberized coating
that gives the correct texture, and custom color match a top coat.

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Old 01-14-2017, 07:32 AM
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Quote:
Originally Posted by onboost View Post
I'm not so sure that U-pol supplied the shutz, SKS to Wurth. Both are world-wide chemical companies one being based in England and the other in Germany. Although, we all know that the grey SKS is no longer available but the U-pol is a pretty good match if not spot on.. so maybe?
I think it was this product that was used originally:

TEROSON TEROTEX RECORD 2000HS CORROSION PROTECTION 1Ltr GREY | eBay.

http://www.loctite.co.uk/loctite-4087.htm?nodeid=8802620047361

Last edited by javadog; 01-14-2017 at 07:47 AM..
Old 01-14-2017, 07:43 AM
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