Painting underbody grey... am I nuts? - Page 2 - Vintage Mustang Forums
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post #16 of 35 (permalink) Old 09-26-2018, 03:45 AM Thread Starter
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Thanks for the feedback everyone; I assumed I would only get one or two replies...

My car is far from stock/concourse as is so one more departure from stock part doesn't bother me.
I have SPI grey epoxy, I will probably just shoot it with a few coats for now and reassess after I see it since I need to get something on the metal.

Maybe I will try some on my old floor pan seat risers and try scratching it up and abusing them with some oil/solvents (once cured) for kicks.
I've heard conflicting information with some people saying epoxy alone is fine and doesn't need topcoating (SPI epoxy does have UV protection in it, not that it matters that much under the car) and others say it should be topcoated. Was just hoping for more of a general consensus vs all the differing opinions. It would probably annoy me if it ended up stained due to oils, etc after a few years so perhaps a topcoat is in order, we'll see.

I still need to weld in the subframe connectors anyway so I can always scuff and shoot another color topcoat (or the same color if it turns out I like it) once the subframes are in.

Thanks again.
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post #17 of 35 (permalink) Old 09-26-2018, 08:32 AM
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Originally Posted by steferg View Post
Thanks for the feedback everyone; I assumed I would only get one or two replies...

My car is far from stock/concourse as is so one more departure from stock part doesn't bother me.
When concours doesn't matter as much as durability....Rust Bullet followed by Raptor
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post #18 of 35 (permalink) Old 09-26-2018, 08:52 AM
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Quote:
Originally Posted by steferg View Post
Thanks for the feedback everyone; I assumed I would only get one or two replies...

My car is far from stock/concourse as is so one more departure from stock part doesn't bother me.
I have SPI grey epoxy, I will probably just shoot it with a few coats for now and reassess after I see it since I need to get something on the metal.

Maybe I will try some on my old floor pan seat risers and try scratching it up and abusing them with some oil/solvents (once cured) for kicks.
I've heard conflicting information with some people saying epoxy alone is fine and doesn't need topcoating (SPI epoxy does have UV protection in it, not that it matters that much under the car) and others say it should be topcoated. Was just hoping for more of a general consensus vs all the differing opinions. It would probably annoy me if it ended up stained due to oils, etc after a few years so perhaps a topcoat is in order, we'll see.

I still need to weld in the subframe connectors anyway so I can always scuff and shoot another color topcoat (or the same color if it turns out I like it) once the subframes are in.

Thanks again.
Steve
One thing to consider, with most primers you have a recoat window. If you exceed the recommended time to top coat, you will need to scuff the primer to insure adhesion. This can be somewhat difficult to do on the underside due to all the shapes involved.

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post #19 of 35 (permalink) Old 09-26-2018, 08:59 AM
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I'm in the "Do as you wish" camp but thought I would show my undercarriage. I wanted to go as original as possible and found when cleaning my undercarriage it didn't even get painted. You can see the nightmist blue over spray but no primer. So I tried to duplicate by painting it with a silver.

See the pictures, I have plenty more pictures also. The only red oxide I could see was a little starting in the rear and a little on the front rails. Not sure what happened in between.

You can also see how well the car has held up with no paint all these years. Check the frame rail galvanizing.

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post #20 of 35 (permalink) Old 09-26-2018, 10:50 AM
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Wow that was a solid bottom, hard to believe they didn't prime it.
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post #21 of 35 (permalink) Old 09-26-2018, 02:23 PM
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Originally Posted by Caper50 View Post
Wow that was a solid bottom, hard to believe they didn't prime it.
If you look real close, you will notice there was no seam sealer on the bottom side either (there was on the interior).

You can see the small amount near the rear and some darker (almost brownish color) on the front frame rails.

The frame rails look like 1966...literally (except for a few dents).

If I recall the procedure correctly, it seems that maybe the front rails were hand sprayed and the thinking is the jets on the automatic sprayers for the bottom may have clogged or ran out of paint so Ford just kept the line moving. That's the theory from Concours , again if I'm remembering correctly. I also think that it was determined that the red oxide on the rear frame rails may have been from the body primer over spray.

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post #22 of 35 (permalink) Old 09-26-2018, 05:55 PM
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Originally Posted by Mach1 Driver View Post
I got this from BuckeyeDemons build thread on another forum:

Klutch said:
Buckeye, it appears you painted the undercarriage a gloss gray. Is that the way your car came from the factory? It looks great!

I thought the undercarriage was supposed to be a shade of red, but maybe that was just the '70 Mustangs. Likely, I'm just confused.

BuckeyeDemon said:
it depends on what plant the car was built at and what day.

can you find any remnants of original paint on yours? i can't speak for all years and plants, but in general, Dearborn used leftover topcoats (all mixed together) to spray on the undercarriage (from the firewall back). so the color of the mixed paint could vary.

on my original undercarriage you can see the grayish color, along with some of the candyapple red overspray and the black from the pinchwelds.

Hey, that's me! I've done a lot of online searching on this subject. The conclusion is it varied a lot depending on where the car was built and when the car was built. My 1970 Mach 1 from Dearborn had gloss black on the bottom from the factory. Some cars had orange. Some cars had "slop gray" which was a mix of whatever enamel they had leftover on the assembly line. So, exactly what shade of gray depended on the particular day.

I used a lot of SPI products on my build. I would suggest you strip the bottom and shoot on one coat of SPI epoxy; gray would be fine. Then apply all the seam sealer. Then shoot on two more coats of epoxy. That's all you need. Yeah, some guys like to put on bed liner or other stuff. I'm in the camp that if I see a car with bed liner on the bottom, I wonder what it's hiding.
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post #23 of 35 (permalink) Old 09-26-2018, 06:48 PM
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If I had the opportunity for a street car I'd use a coating specifically for underbody. As far as epoxy primers go SPI is one of the best but it's not going to be as durable as an underbody coating. Being "waterproof" isn't the issue. That pertains to not soaking through to the substrate and corroding. It's the abrasion protection and the possibility of wear and chipping. It's not water that does the damage but the particulate matter that's kicked up on to it. If you're only driving a couple thousand miles a year in mostly dry weather it won't be an issue.
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post #24 of 35 (permalink) Old 09-26-2018, 10:03 PM
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Originally Posted by steferg View Post
Was just hoping for more of a general consensus vs all the differing opinions. It would probably annoy me if it ended up stained due to oils, etc after a few years so perhaps a topcoat is in order, we'll see.



Thanks again.
Steve
I'll add to the trend then. It needs some type of top coat over primer in a timely manner. Even if its Rustoleum from Autozne.
I read grey underbody and i think race car, anything besides black is good for seeing leaks and damage.
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post #25 of 35 (permalink) Old 09-26-2018, 10:34 PM
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The underside on mine is going to be the same color as the top. I'm also using a gray epoxy primer and thought about just leaving it in primer, but the epoxy primer is not UV resistant. I realize it is on the bottom, but still can be affected by UV at the wheel wells, etc.
SPI Epoxy is UV resistant

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post #26 of 35 (permalink) Old 09-26-2018, 11:08 PM
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SPI Epoxy is UV resistant
Barry at SPI doesn't recommend it. He says many factors contribute but you can't exactly say when it will fail. He says there are too many variables to say for certain but he recommends not using it without a top coat. He's been asked that more than once. People dig the shade. That said it tends to hold up better than others even over the period of months of direct sunlight and some have used it as a finish. I was thinking of using it on the underbody of a street legal off road race truck. I ended up using a steel impregnated industrial coating called Steel It.

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post #27 of 35 (permalink) Old 09-27-2018, 12:37 AM Thread Starter
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Hey, that's me! I've done a lot of online searching on this subject. The conclusion is it varied a lot depending on where the car was built and when the car was built. My 1970 Mach 1 from Dearborn had gloss black on the bottom from the factory. Some cars had orange. Some cars had "slop gray" which was a mix of whatever enamel they had leftover on the assembly line. So, exactly what shade of gray depended on the particular day.

I used a lot of SPI products on my build. I would suggest you strip the bottom and shoot on one coat of SPI epoxy; gray would be fine. Then apply all the seam sealer. Then shoot on two more coats of epoxy. That's all you need. Yeah, some guys like to put on bed liner or other stuff. I'm in the camp that if I see a car with bed liner on the bottom, I wonder what it's hiding.
My initial plans were to undercoat the entire bottom after stripping, priming, and seam sealing.
But then i spent forever cleaning off 50 years of crap I didn't want to cover it up with a bunch of undercoating.

Regardless of what I do It is likely the car will be better off than it was from the factory.
It seems like everything behind the differential got a thinner coat of paint (or nothing maybe) because everything from the differential back seemed like surface rust I was removing instead of paint.
It was bizzare. I guess it could have been red oxide but it looked more like rust to me and I didn't see anything that looked like red at all anywhere else on the underbody.
There were also a bunch of seams that were not sealed at all from the factory (there were some seams that were sealed on one side of the car but not the other, etc).
I'm glad this car was in Southern California it's entire life...

I plan on driving this car daily during good weather; but realistically if I put 10000 miles on it a year I'd be surprised.

Man i hate decisions like this.
I really should just get it done and move on to more fun stuff.

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post #28 of 35 (permalink) Old 09-27-2018, 12:55 AM
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Originally Posted by steferg View Post
Regardless of what I do It is likely the car will be better off than it was from the factory.

Put epoxy, seam sealer and more epoxy and you are light years ahead of 60's factory. Then you can coat with whatever you want.

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post #29 of 35 (permalink) Old 09-27-2018, 07:58 AM
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Here is mine,1966 Calif built with all original metal
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post #30 of 35 (permalink) Old 09-27-2018, 12:29 PM
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I've always appreciated the light grey/off-white interiors and undersides of NASCAR cars, as the colors must make it easy to see and work on things. I would consider a nice grey painted underside to be a plus in my book, so long as it's not all gunked up with dirt.

So, as others have said, do as you please and don't look back.

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