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Author Topic: GM Heritage Center Documentation / Underbody color  (Read 6512 times)
DavidS
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« on: January 05, 2012, 09:14:52 PM »

I am not sure if this info has been posted but these documents have a lot of GREAT info:

1967 http://gmheritagecenter.com/gm-heritage-archive/docs/Camaro/1967-Chevrolet-Camaro.pdf

1968 http://gmheritagecenter.com/gm-heritage-archive/docs/Camaro/1968-Chevrolet-Camaro.pdf

1969 http://gmheritagecenter.com/gm-heritage-archive/docs/Camaro/1969-Chevrolet-Camaro.pdf

For a long time, I have been curious about what color the underside of a 1969 Camaro should be.  There were quite a few postings that the color black on the underside of a Norwood car is the stuff of showcars.  After reading page 49 (as labeled on the page) "Exterior Paint Process", I would tend to agree that original undersides were primer color.
« Last Edit: January 11, 2012, 03:00:37 AM by KurtS » Logged

69Z28-RS
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« Reply #1 on: January 06, 2012, 12:31:21 AM »

underside seems to be primer with areas of 'body color' overspray, as they sprayed the lower portions of the car body the underside got some body color..
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Gary W.  /  69Z28-RS, 72 B 720 cowl console rosewood all tint
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DavidS
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« Reply #2 on: January 06, 2012, 06:58:14 AM »

Agreed.

I have a 69 Z/28 being restored and there were a few sections that had been repainted but it never had a complete repaint.  Here is the underside:



However, for judging, my understanding is that it should be black and not primer color.

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lakeholme
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« Reply #3 on: January 06, 2012, 08:20:23 AM »

Especially the AMA charts. Same as the snail mail package you could request and same poor quality on a few pages, but it's great to have them downloadable. Thanks for sharing!
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Phillip
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DavidS
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« Reply #4 on: January 06, 2012, 10:57:10 AM »

The question of what color to paint the underbody is not a trivial one for me.  My hope is to have the Z/28 as a judged trailer queen for a few years and then use the car for local driving and car show.  I am trying to have it restored as correctly as possible.  But if there is a deduction of points due to the underside not being black then I am not sure what to do  Huh  Huh  Huh

The car will probably be ready for paint in a few weeks.

I have read through the GM info:
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EXTERIOR PAINT PROCESS

1. RUSTPROOFING.  Assembled car bodies are chemically sprayed to clean and etch the metal surfaces for corrosion resistance and paint adhesion.  Unassembled sheet metal parts follow the same process.

2.  BODY AND SHEET METAL PRIMERS.  Four corrosion resistant primers, specially formulated are had sprayed on the body in areas where rust might develop.  Lower areas considered especially vulnerable are coated with another rust inhibiting compound.

3.  PRIMER COAT is applied to all outside and inside surfaces of front fenders and hoods.  The parts are mechanically dipped or flow-coated to insure coating in all seams and secluded areas, and baked at 390 degrees F for 30 minutes.  A coat of sealer is then applied by hand spray to all surfaces requiring another coat of lacquer.

4.  FLASH PRIMER AND PRIMER-SURFACER COATS.  An air-dry flash primer coat is hand sprayed on surfaces below the body belt line.  Then a gray primer-surfacer coat is hand sprayed on all outside surfaces of the body and oven baked for 45 minutes at 285 degrees F.

5.  INITIAL SANDING.  Power wet sanding, followed by hand sanding, is done on all body surfaces requiring lacquering.  This insures a smooth surface for the lacquer finish.  To remove the water, the body is wiped and run through an infra-red oven.

6.  LACQUERING.  Three coats of acrylic lacquer are spread on the exterior surfaces of the body and sheet metal parts to build up a finish of the required thickness for each color.

7.  INITIAL BAKING………….etc through step 11.
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JohnZ
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« Reply #5 on: January 06, 2012, 02:42:41 PM »

<<The question of what color to paint the underbody is not a trivial one for me.  My hope is to have the Z/28 as a judged trailer queen for a few years and then use the car for local driving and car show.  I am trying to have it restored as correctly as possible.  But if there is a deduction of points due to the underside not being black then I am not sure what to do >>     



Have you read the Fisher Body Paint Shop portion of the First-Generation Camaro Assembly Process Report? Painting the underbody black is a typical restoration mistake.

http://www.camaros.org/assemblyprocess.shtml
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DavidS
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« Reply #6 on: January 06, 2012, 02:59:33 PM »

Have you read the Fisher Body Paint Shop portion of the First-Generation Camaro Assembly Process Report? Painting the underbody black is a typical restoration mistake.

http://www.camaros.org/assemblyprocess.shtml

I did read that John and that's why I started researching this.  I believe you are absolutely correct.

What is baffling is that it does not seem to be just a restoration mistake, but it is a widespread held belief that they should be black.  From very high end restoration places to judges.  However, it is documented both through you and through GM that the underside is  primer.  At that point, it's not a subjective issue.  It is GM documented, historian documented, and at least on my car is proven out by physical evidence.
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Mark
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« Reply #7 on: January 07, 2012, 08:38:30 AM »

Coverage of the primer is also different from one plant to another, the bodys at norwood sat on trucks that rolled along tracks on the floor with the bottom of the body about 18" off the floor, while the bodys at LA hung from a ceiling mounted track which allowed more access to the underneath portions of the cars.   Your lucky if the center area under a Norwood car got anything more than a light dusting of primer.  Body color was not painted by humans, but by fixed and reciprocating spray heads along the sides and top of the spray booth.  Think of a car wash that sprays paint instead of water, no one painted the main body color by hand at the plant, except in the repair booth area to fix damage and or missed spots.  Stripes and blackout treatments were painted by hand later in the process.
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Mark C.
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DavidS
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« Reply #8 on: January 07, 2012, 10:45:46 AM »

Thanks Mark.  The information from you and JohnZ are very helpful in understanding how things should be restored. 

For incorrect black underbody restorations, I have two theories how it started:

Theory 1)  In the GM instructions, Step 1 (etching) and possibly Step 2 (rust inhibiting compound) left areas that were black.   This caused people restoring cars today to believe that the underside must have black. 

Theory 2) People believed that black looked better or was more durable than primer.  They started restoring cars this way and it became accepted practice.

Out of the huge number of restoration pictures I have seen, I have only seen one underbody that was primer color.
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68Zproject
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« Reply #9 on: January 07, 2012, 11:52:04 AM »

Just to clarify, what color is the primer on the underside?
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68Z28
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« Reply #10 on: January 07, 2012, 12:11:11 PM »

... I have two theories how it started...
A third could be that is was very common (at least in the rust belt) for dealers to undercoat cars.  The underbody on my car was completely covered in black undercoating.  It sure saved the floors, so I left it.  Not factory correct for judging, but 'as-delivered' correct.
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« Reply #11 on: January 07, 2012, 01:51:43 PM »

David Thanks for posting the links for the documents that kind of information is a tremendous asset to us restoring cars. I researched allot of original cars trying to understand how my car was originally painted. The assembly information that JohnZ provided really answered a lot of my questions but then I looked at other clues and other cars and had more unanswered questions. 35 years ago I worked for a shop that had more original low milage original Corvettes & muscle cars come thru the doors than any other shop that I can remember at that time. This ingrained me with a believe that originality & restoring it as it left the factory is most important to my restoration.
My car came out of Colorado, was covered underneath with oil, grease, and sandy dirt. All of witch saved the bottom of the car finish. After cleaning it I found really nice original BLACK paint. At the front of the tunnel and low on the firewall I see grey primer misting back OVER the black paint but just 6-12" back on the bottom of the floor. The firewall blackout paint is sprayed over the grey primer above this area. This same grey primer was found inside the car and under the vinyl top. Apparent that the factory didn't paint the entire roof if it was getting a vinyl top. In the trunk area I found red oxide primer on the top of the rear seat panel and near the lock support. At that point I didn't know how I was going the paint the bottom of the car. After cleaning I believe the bottom was painted black, the outside surfaces and in the trunk were painted red oxide primer, then the topside painted panels, and inside overspray, were painted grey filler primer. I will post a couple pictures showing what I found on a Norwood car built Nov 1968.
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NoYenko
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« Reply #12 on: January 07, 2012, 02:28:45 PM »

A couple other related pictures. I can't understand why there is no paint under the one exhaust hanger and I would have thought the blackout paint on the rockers would have been painted after the front end was on but this picture shows a masked line over the Lemans blue on an area covered by the fender normally.
I have other pictures if you are looking for more.
I really enjoy these kind of posts, Thanks.
George
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DavidS
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« Reply #13 on: January 07, 2012, 04:44:45 PM »

Wow!  NoYenko, I did not expect to see so much black primer.  When I look at the GM instructions, the last step with primer is step 4 and it is a gray primer.  If black primer was put on it would have been done earlier in step 2 when the instructions say 4 corrosion primers were put sprayed on by hand.

Jeff68, your 3rd theory sounds reasonable too.  

I have a 4th theory: There is too much variation considering 4 corrosion primers applied in GM instruction step 2 and the gray primer applied in step 4.  To make judging guidelines uniform and make the underbody look neat and tidy, everyone should paint their underside floor pans 30-percent gloss black (and add a little overspray).

Also, I could not find specifics in JohnZ’s write up where black primer was put on.  

from JohnZ
---------------------
"Prime System: In the first prime booth, the entire body, inside and out, was manually sprayed with primer, and confined areas subject to corrosion were given a second coat of heavier primer material; this prime coat was then baked at 390F for 30 minutes. In the second prime booth, the instrument panel and rear of the shelf area (and the upper door and quarter areas of 1967-68 models) were painted interior color, and another coat of air-dry flash primer was sprayed from the belt line down. The interior color areas were masked, and the entire outer body was sprayed with gray primer-surfacer and the body was baked again at 285F for 45 minutes."

Based on the GM instructions and John’s write-up, I would expect the majority of the underbody to be gray primer.

68Zproject, you have the bottomline question:
what color is the primer on the underside?
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Mark
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« Reply #14 on: January 07, 2012, 05:02:28 PM »

Black paint, or black phosphate coating?
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Mark C.
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