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Old 12-25-2005, 01:42 PM
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Paint cracking...now I'm cracking!

Okay, here's the story. 66 mustang/289 stripped to bare metal then bondo work then etch, then high build primer. Painted with Omni urethane (no clear coat). Looked good, then started cracking along the sides where the qtr panel meets the roofline. Welded in subframe connectors as unibodies have a lot of flex. Fixed cracks and repainted. Things were fine until after about another year...yep, more cracks along the qtr to roofline and also on the roof there is one area that has cracked twice. What is the problem? I hate doing body work over and over again What do I do to stop the cracking? Is it just cheap paint (omni)? I am going with a basecoat/clear this time so someobyd steer me in the right direction before I run this thing off a cliff or something! Heres a couple of pics where I replaced the qtr on the passanger side, but oddly enough the drivers qtr is the one cracking!
http://www.freewebs.com/gwstang/

Thanks for replies/help so I can get this started and repaint in the spring...gary..going nuts in Eclectic, Alabama...right down the road from Kowaliga (yep the Hank Williams Kowaliga)

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Old 12-25-2005, 06:31 PM
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A couple of things come to mind. Is the cracking in the paint or the body work? If it is in the body work, I would think that the quarter may have been replaced on that side in the past, and possibly the joint is broken loose. If it is just the paint cracking, it may be a problem with the primer reacting with the metal/filler under it.

Something to look at.

Aaron
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Old 12-25-2005, 06:38 PM
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Paint cracking?

When you reworked these bad areas was just the paint cracking? The body filler covering the joint may just be thick enough not to be flexing causing the cracking. Temp changes will cause this too. When the metal expands and contracts and the paint material is too thick to be flexible it will crack or spider web.
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Old 12-25-2005, 06:47 PM
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Like the above posts stated we need to find the source.
Best way to do that is take a razor blade and a little at a time cut on the crack until it stops.
Does it stop at the weld?
Does it stop at the primer?
Does it stop at the acid etch?
Does it stop at the filler?

Could be a bad weld, a weld that was not cleaned, acid etch reacting with the lead, primer melting the acid, to heavy of primer.
We have a lot of choices and if you can tell us where the crack stops we can help.
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Old 12-26-2005, 08:42 AM
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Where these cracks are you've got either stress causing the crack or an open seam that's been covered with bodyfiller. Originally these cars used lead to blend in the seam where the quarter meets the roof, the solder did a good job and would flex and adhere just fine to the lap joint in these areas. But when body filler is used in place of solder the seam should be welded completely with no open edges, just spot welding the joint is not good enough if filler is used. You'e going to need to strip these areas back down and find out what the problem is. If the cracks are stress induced then a reinforcement from the backside may cure the problem, panel adhesive can work good for this if you have access.
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Old 12-26-2005, 10:31 AM
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Sure sounds like a failure of the seam in some way. If if was not welded completely closed that will need to be done at this time, followed by an initial coat of filler that is stronger than regular plastic filler, like kitty hair or everglass. I think you are going to be stuck painting the roof and quarters again, but this time you ought to really dig deep and kill the problem once and for all!
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Old 12-26-2005, 02:15 PM
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It is very common for a car such as this to crack right where the quarter meets the roof, a verticle or diagonal crack running away from the corner of where the roof meets the quarter. It happens because of the vibration of the quarter as the door is shut. Go out and roll the quarter window down. Hold the top of the quarter right at the door lightly and have some one else open and shut the door, you will feel a slight vibration. That vibration is STOPPED right where the quarter meets the roof, THAT is where all the vibration is absorbed. So like folding a beer can back and forth a number of times you can tear it in half, a crack appears.

It is also very common to see where the guy who hung a quarter doesn't weld all the way around the back of the lip in the quarter window to properly support the quarter which of course accelerates the failure.


Does this describe the crack?

Brian
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Old 12-26-2005, 07:35 PM
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Arrgghh, I had this long reply typed and the computer froze up Okay, I will try answersing the quesitons again.
The one thing I have noticed is that the crack only goes thru the paint and not the filler below. Is this because the filler is too thick as mentioned? Also, the cracks are isolated and rather large and occured in the same area as before. The roof had been thru a terrible hail storm at some point so I had to use alot of filler on the roof and roofs are thin so it is probably flexing too much. I may just have to go with a vinyl roof to cover this up. Where I had to use the filler sorta thick, I did use the fiberglass stuff, then a thin layer of regular over this. I used the "Rage" body filler. I think this is Evercoat and is supposed to be good stuff??? The paint system I used was Omni 2 part epoxy primer/Omni Urethane Candleapple Red so there should be no diverse reactions between the two as they are recommended by ppg to be used together. The qtr that is cracking so bad is the original and has a lot of bondo in it. The side I replaced is doing okay so far. I did have to melt the lead out of the side I did...that was fun. I can get to the back of the roofline/qtr where they meet from the inside by pulling back the headliner on that side, if I need to apply something on the inside to strengthen that area???? I am going to take some pics of the areas tomorrow (rain has finally quite and sunshine prevails) and will post them if ya'll would be so kind as to check back tomorrow evening. I do have one idea (crazy), could something like the additive that is put in paint for using on a bumper (new car bumper) so it can "flex" work on my car? Why couldn't I just put some of that in the next time I paint so it would flex a little better? Since these old unibody cars have so much built in flex....just an idea Thanks again for everyone's interest and help/suggestions on this...gary.
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Old 12-26-2005, 08:37 PM
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Post the photos, that may be of help. Post one showing the area they are at and then one closer.

Other than a HUGE build up of solvents do to piling on primer or something and then force drying the paint so you have a "shell" over the solvent soaked primer, I don't have an idea. If the filler isn't cracking, but ONLY the paint, that is pretty strange. That paint will flex more than anything so it isn't the filler or something that is failing under the paint, wow, don't know.

How about moisture? Hey, that could be it. Is there ANY WAY where these are that water could be getting under it? If it is near a seam like the roof gutter or something where the paint and or primer is forming a "shell" and then water gets under it lifting it up and cracking it.

Brian
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Old 12-27-2005, 08:02 AM
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You know, that reminded me that a fellow I met once at a show mentioned the water getting under there and causing this. He did body work on all the troopers cars down here, until he retired. Built some beautiful rods. I did the seam sealer after stripping the car, way back. One things for sure, once it does crack, it opens it up for moisture to enter... I'll get the pics up by this evening.
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Old 12-27-2005, 06:09 PM
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Heres the pics

http://www.freewebs.com/gwstang/must...ckingpaint.htm

See if ya'll can take a peek at this link...thanks so much for everyone's help/opinions/comments etc...gary.
I am ready to do whatever it take to fix this right!
The last pic is the one of the roof.
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Old 12-27-2005, 07:11 PM
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I haven't worked on Fords very much but the filler looks like it is lifting and cracking. You definitely need to look at the look at the metal behind that area and see how it was previosly repaired. I think we have all seen some nasty things behind filler. Look at it this way it is a good excuse to go to the base/clear you mentioned you wanted to do. I have used omni on boats before which are fiberglass they flex quite a bit and it still last a good while. Even though it is inexpensive it still works well.
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Old 12-27-2005, 07:41 PM
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There's a combination of problems here from what I see. The spidered crack right behind the rear corner of the quarter glass is definately stress related and I'm thinking the metal is probably cracked as well. There's also evidence of adhesion problems higher up along the sail panel supported by how the filler is lifting up and away. The last pic looks like a product of corrosion under your filler. You're going to have to dig it all out and take some more pics for suggestions on how to cure the problems. Bob
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Old 12-28-2005, 03:11 AM
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I am not a paint expert, but it definately looks like the cracks are not only in the paint. The "spider cracks" do look like the same type of stress cracks I have seen many times on doors and quarter panels in similar areas. The one at the drip rail looks like it may not have been cleaned enough, or sealed good, and got moisture in there. The seam sealer there in my 67 Stang was in really bad shape. It was hard to dig it all out, and even harder to get it in there real good, and get good paint there.

Aaron
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Old 12-28-2005, 05:28 AM
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The non seam cracks looks like a combination of
loading of primer and water in the are line because of the pattern of the cracks.
If those cracks were cause by just water the would be straight like done with a scalpel such as your body line crack at the left edge of the picture.

I also think the crack in the drip rail are is loading of primer also by looking at the cracks.
Here again in those areas a razor blade will tell the story as pointed out before.

Either way the whole area has to be stripped and started over from welding on up.
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