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 Dealing with rust/pitting on hood.
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Bill Boyle
Horse Feathers (Charter Member)

USA
4793 Posts

Posted - 30 Jan 2012 :  7:54:12 PM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
On the hood of my Trans Am two inches from the very front of it I noticed several tiny bubbles in the old paint. Today I took sand paper to those spots and cut down through all the paint and substrates to the metal. I could see blemishes or pitting. There was no rust, no rusty colored material. I then hit the areas with a small wire brush and picked at those areas. Definitely pitted spots in the metal. Size-wise, less than 3/32" in diameter.

These areas need to be treated so for the time being I hit it with several coats of black primer. This is temporary as it will need to be reexamined when the car is prepped for new paint.

All paint will eventually be removed and all problem areas will be addressed by the paint shop. What method(s) are they likely to use today to prevent recurrence of this in the new paint? Any expert paint and body men out there?

"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Hedman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.

mike mcarthur
Pony that Jumps

USA
2475 Posts

Posted - 31 Jan 2012 :  06:20:58 AM  Show Profile  Visit mike mcarthur's Homepage  Reply with Quote
Were the pits there the last time it was painted? If so the likely was rust that was removed and the pits were covered with primer. The subsequent failure of the top coat has caused moisture to likely penetrate and cause what you are seeing now. I have a small spot blaster with glass bead that I use for small stuff like that to remove any rust. Once that is done and the car properly primed and painted you won't have an issue.

It's the stuff you learn after you know it all that's important
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Bill Boyle
Horse Feathers (Charter Member)

USA
4793 Posts

Posted - 31 Jan 2012 :  07:52:47 AM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
Mike--
I took great pains during my last paint job to spot any suspect areas. I don't recall seeing anything there but I could be wrong--its been 19 years. During the sanding process to uncover the pitting, several layers of paint and substrates of primer and sealer were removed. [Metal, pastel yellow, red oxide, gray primer, base coat blue, cc]

It's very possible that moisture found it's way down through the worn out base coat/cc. I'm hoping my temporary fix with black primer will thwart any further rusting/pitting of those spots. The car sits in the garage so that should keep things under control.

I have to remove the window moldings front and rear to check those areas for any signs of rust. It was solid 19 years ago.

"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Hedman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.

Edited by - Bill Boyle on 31 Jan 2012 07:53:42 AM
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Aguila1
Buffalo

USA
85 Posts

Posted - 21 Feb 2012 :  11:23:40 PM  Show Profile  Reply with Quote
I just want to add that bubbles in the paint are often caused by tiny pinholes in the sheetmetal. What that means is that you might have rust-through and unless you repair that hole with new metal, bubbles will keep coming back - after your expensive paint job is done.

1979 Pontiac Firebird Trans Am custom, shaved, House of Kolor Kandy tangerine base coat, airbrush graphics, 462 w/ 1968 #16 heads, 13:1 compression, Ross pistons, Crower Sportsman rods, Pro-Gram billet 4-bolt main caps, Crower 60919 cam, 4L60, powered by e85.
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Bill Boyle
Horse Feathers (Charter Member)

USA
4793 Posts

Posted - 11 Mar 2013 :  3:10:19 PM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
Jos--
Your advice was taken. Upon further examination of the pinholes, it turns out they are much worse than I expected.

Today, I sanded the areas with the bubbling. When I got down to the metal, I could see small pitting. At first I thought this wasn't too bad, however, I took a small screw driver and probed the spots. They were not solid. The edge of the screwdriver dug in and after some wiggling penetrated through the metal. I did this to all. Only one spot turned out to be nothing but a blemish in the metal. Thereafter, I drilled a small 1/8" hole. The metal was no good. I moved up to 1/4" than up to 5/16" drill bit where the metal was solid.

Below is a photo of the area in question which is on the driver's side of the front of the hood.

My bet is this. The top metal is one sheet and under the hood is another. They meet close to the front of the hood and are crimped over to form the edge of the hood. There's a tiny space between the two sheets of metal, enough to allow condensation to form between the two. Over time, in this case over 30 years, rust has managed to eat through the top metal.



My concern is how best to fix this problem. I realize that a rectangular piece of sheet metal could be cut out and replaced with new sheet metal and mig welded in place. This is problematic as I don't own a mig welder to do the job. If I take the hood to a body shop to do this, it will be on their back burner for months as this is not a money maker for them. I have oxy-acetylene, but I'm not very skilled with it, and don't want to over heat the metal and warp it. Bondo is temporary as it won't hold up in an area like this where the hood is opened and closed and flexing of the metal. What about using body solder (non toxic lead) melted over the holes and sanded flush? Thoughts?

If replacing the sheet metal is truly the best, where can I purchase appropriate gauge sheet metal for such a repair?

If I have to, I'll outfit my garage with a small Mig welder to do the job.

Another choice, I suppose, would to to purchase a brand new hood.

What do you body guys think?

"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Hedman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.

Edited by - Bill Boyle on 11 Mar 2013 3:26:06 PM
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cortcomp
Coyote

USA
5335 Posts

Posted - 11 Mar 2013 :  4:27:35 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
For me, when it comes to body work, if i could find a used hood, i'd do that and avoid the job altogether. Other than that i would weld with the mig welder if you can rent one, even a flux core one, and use a sand paper frap /blending disc (120 grit will be good for this) to level it down to the metal around it. Repeat to fill anything you missed, then i'd fill with bondo, just a skim coat, then sand it down flat. (i'm usually lazy on the last step, and just put 320 on a DA and work it quickly.)

The frap blending disc doesn't gouge the metal as much as grinding, and a skim coat and some fine sand paper gets it ready to paint asap. Only down side is, in a flat area like the hood, you can't cheat with the da if you get a large low area, gotta block it out.

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cortcomp
Coyote

USA
5335 Posts

Posted - 11 Mar 2013 :  4:29:08 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
This is my magic wheel, durable enough to grind down welds, but not dig too deep if you dwell on an area for a second:



I have no idea what its correct use is, that's just what i use it for.

Edited by - cortcomp on 11 Mar 2013 4:31:28 PM
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Kiwi Mal
Cochise

New Zealand
690 Posts

Posted - 12 Mar 2013 :  02:04:24 AM  Show Profile  Reply with Quote
If it is like that there then it is probably close to coming through in other ares. The other side of the hood could be nearly the same.
I suppose it comes down to how much paint got in there when the car was fist painted.

Have a good look where the two skins are crimped together. Make sure that it is not expanding due to rust between the skins. If it is you are in for a lot more work by un-crimping the the front of the hood and removing the rusted area.

If you use bondo for fairing you should firstly spray the bare metal with an epoxy primer or it will become a moisture trap between the metal and bondo. Then it all happens again.
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bnorris_74
Crazy Horse

USA
1442 Posts

Posted - 12 Mar 2013 :  06:54:37 AM  Show Profile  Reply with Quote
Bill
You have oxy/acet, try brazing it. Doesn't require a lot of heat so warpage will be minimal and bondo should finish the job nicely. Plus the brazed spots grind down easily.
Make sure to get all the flux ground off the spots though. The flux will pop off later and ruin your paint job.

Edited by - bnorris_74 on 12 Mar 2013 06:57:05 AM
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Lucas
Cochise

USA
428 Posts

Posted - 12 Mar 2013 :  8:57:50 PM  Show Profile  Reply with Quote
I too would find a good used hood. Rust isn't called cancer for no reason. It hides and the more you cut out usually exposes more. If keeping the original hood is really wanted then patching can be done but as stated by Kiwi Mal it probably isn't to far from coming through in other areas. I would avoid flux core welding as you end up with so much clean up you run the risk of warping at several steps from the welding to the grinding. If you find that the rust isn't much more then what you have found now, you could also simply weld your holes you drilled closed. Granted this is tough on such thin sheet metal but I have done this in the past with good results. And then a good glazing putty will smooth it out nice.

"wildfire"
Real pontiac power
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Vanmor
Cochise

USA
573 Posts

Posted - 30 Jan 2014 :  9:48:03 PM  Show Profile  Visit Vanmor's Homepage  Reply with Quote
I have some of that on my trunk lid. I hope it ain't bad !

"A man has got to know his limitations." Dirty Harry
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Bill Caprio
Tribal Scout

21 Posts

Posted - 10 Sep 2014 :  09:26:46 AM  Show Profile  Reply with Quote
How did you end up repairing this area?

Bill Caprio
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Bill Boyle
Horse Feathers (Charter Member)

USA
4793 Posts

Posted - 10 Sep 2014 :  3:32:49 PM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
Bill--It's still awaiting work. Too many other things going on.

"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Hedman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.
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Bill Caprio
Tribal Scout

21 Posts

Posted - 15 Sep 2014 :  6:12:16 PM  Show Profile  Reply with Quote
I hear that.

Bill Caprio
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