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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.

Allen
 

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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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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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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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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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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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Discussion Starter #27
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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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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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.
SPI instructions indicate epoxy without is fine for frames and underneath the car. Those areas are not directly exposed to sunlight. Anyway, I shot three coats of SPI epoxy on my car, then top coated with black Eastwood chassis paint simply to make it look factory.
 

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Since everyone likes to see pictures...
 

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SPI instructions indicate epoxy without is fine for frames and underneath the car. Those areas are not directly exposed to sunlight. Anyway, I shot three coats of SPI epoxy on my car, then top coated with black Eastwood chassis paint simply to make it look factory.
He specifically told me in an email that he didn't recommend it even though it was done. You'd still have the potential for abrasion issues as mentioned before but that's going to be the case with most any automotive topcoat.
 

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I check out the SPI user forum almost daily and from what I can gather, Barry says if you let the epoxy induce for at least for hours, it'll be virtually indestructible and can be used anywhere without a topcoat. At any rate, it'll be tougher than any non bedliner type topcoat.

My cars underside was coated in red oxide PPG DP epoxy 18 years ago and outside of some dirt and a few stains, it looks like the day it was put there.
 

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Discussion Starter #35
Well I got it in grey epoxy a few weeks ago, I figured I'd at least update the thread to show it.
I still need to do subframe connectors, seam seal, sand/scoff, then re-coat with whatever the final color will be.

I like the grey, but I think I will probably end up with black since I will want to black out the pinch welds and other things sticking down anyway.
I figure if I am going to do that, I may as well just paint it all black... we shall see.

 
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