Weld seams showing through new paint job

[Rick Giles]

To all the real welders out there, sometimes when a patch panel such as a 80% quarter panel is put in with a mig welder the impression shows through the new paint job months or years later, especialy noticable on a nice wet sanded paint job. Is it because of bad prep or not cleaning the weld properly before using body filler and primer?

[MrQuick]

I would think it was due to filler shrinkage. Not enough prep time?

[Jim Nilsen]

On my 1st 67 camaro I put a laquer paint job on it myself and the leaded seam at the roof line would always start to show with an orange peel look after about 6 months and then I would buff it and it would go away. It was always a mystery to me.
I painted my 67 that I have now and it has never done the same thing. I used acryilic enamel on the new paint job with an epoxy primer. The best I can think of is that it is the primer that causes it to happen. I used a sandable primer only on the first car instead of an etching type primer sealer as a base. I didn't have a lot of money to buy the paint much less the right primers at the time. So my guess is that it is either the fault of the primer job not being done very well or with inferior materials . I really don't think you have laquer paint but I don't know that for sure.

So it could be the bondo?

Maybe some will have an explanation for what makes it happen but I understand your frustration.

[Rick Giles]

I was curious if it had anything to do with the actual weld. And maybe not the bondo/primer application or the product used. I've seen this on some cars. And the reason I'm asking is I have a 69 Camaro with the original quarters with rust issues in the usual areas over the rear tires. But it has an awesome fit around the trunk lid. I really hate to mess that up. Not to mention all the factory joints and welds. Just don't want to have the same problems with the quarter patches later with weld lines coming back.

[Hammered]

I've seen what you're talking about and it was definitely after a nice finish was already attained. I would guess the metal was overworked in the weld area or the weld ground too thin.

I've seen a lot of work, butt and lap welded that still looks good after many years.

[xtrmeta]

I believe it's a cemical reaction by some of the paint products.
It happened on my T/A and my truck.
On my T/A all the body work was done about two years before it was painted. The car sat with the final primer already block sanded out to 600. Gave it a once over and painted and buffed it. It looked great. Then about two weeks later the welds appeared.
I used PPG's Global line.
I welded a hood scoop on my truck also using PPG and the same thing happened.
The T/A was epoxied primered first then high build.
The truck I just used a combination high build sealer.
So I belive it has nothing to do with the prep work. I spent three years doing body work on the T/A to make it perfect.
I think it's the paint when it dries shrinking everything under it.

[SatisTraction]

it is refered to as ghost lines and i have been told it is because the original metal and the new metal expand at a different rate.

look up ghost lines on any body forum.

[scotzilla]

it comes from the metal being differnent thickness- Its really important to get the filler panel flush and ground to the same thickness, You see it all the time with those mini truck dorr handle shave kits

[jaybee]

It also tends to happen where you do a lap joint instead of a butt weld. The double thickness metal reacts to changes in temp and especially heat from sunlight differently.

[gearbanger]

That happened on mine. I dont think it has to do with aftermarket sheet metal, or the lap welded joint reacting to heat from sunlight differently. Mine shows up in the garage or in the sun the same. Mine did occur a few weeks after being painted though, the same as everyone elses. I have PPG acrylic enamel on mine, no clear.

My body guy overlapped the panels and welded them solid, ground the welds down, then went over them with a short hair fiberglass filler. Then he skimmed it with plastic filler and primed and blocked until it was straight and slick. It looked great for a while but you eventually could see every inch of the welded seams. I really think it is more of a shrinkage of the fillers over time.

Butted or lapped, I think if the filler has any thickness at all, its going to shrink and show. It might evern be a reaction of the solvents in the paint with the fillers that it is being spryed over. I dont know if some kind of sealer before paint would have helped or not. Maybe?

[BritishGreen68]

It is the filler shrinking over time. Basically if the filler has something to shrink into, it will. If you look at cars like the one Foose does and Rad rides, you will not see this shrinkage. Why? Because they are "metal finished". Meaning even in bare metal, you cannot see any evidence of a weld. The welds a finished perfectly smooth and even by looking at the bare metal you cant tell it was welded together. 99% of shop dont do this because it takes ALOT of skill and time. If there are no welds, how can filler shrink into them right?

[xtrmeta]

It has noting to do with metal thickness or from the filler shrinking. The filler will shrink but in the case of my car it sat for two years before being painted.
There were no visible welds showing anyplace on the car.
It looked great till it was painted.
I just recent welded a metal hood scoop on to my Dodge ram. I cut out the part of the hood and flush welded in the scoop and did all the body work. Epoxy primer, then high build primer, then sealer then the paint and now a few spots are showing through.
I still believe it's something in the paint causing it.

[LateNight72]

Was the seam welded solid?

[xtrmeta]

Yes it was. You couldn't even tell the scoop was welded in. It looked like a factory hood. About a week after it was painted you could see a line around it where the weld was.

[truckeez]

Hi I'm new here this is my second post. I like to go over any seam I splice- weather it is a butt weld or a lapjoint- with a epoxy putty product called marine tex that is avalable at most marine/boat stores. The main reason is polyester-bondo- absorbs moisture and if there is any way for moisture to get at the backside of a weld-bondo wil wick it and SOONER or later it will rust under your bodyfiller-somethings gonna pop loose. Another reason is it is much more stable and does not shrink like bondo so I use the marine tex first--making sure to wear a good mask-dont breathe the dust from this--or any other filler, and then go over it with evercote metalglaze. The marinetex sands easily.

[BritishGreen68]

I do autobody for a living, my dad was a bodyman, my friends are body and paint guys. Its the filler and the materials shrinking up over time. Unless there is some other issue of adhesion between the products you are putting on, but it would be random bubbles not just exactly where the welds are. Metal finished means you can almost go straight to primer from the metal work with no filler. That's what you should be working towards anyway.. here's something i did, i used filler over it but just a glaze (blaze glaze) and this will never shrink up to show the welds.

[John Wright]

I'm glad that I ran up on this thread, I've heard some say that the flux in the center of the fluxcore welding wire was causing these welds to show through paint sometime down the road. I couldn't see how this would be happening but then I'm not a body/paint guy either so I was taking them at their word. I'm glad to hear that if done properly these welded seams will not show through.

[gearbanger]

If you are using a mig (with gas) you aren't using flux core wire any way so that wouldn't be it in most cases I wouldn't think. I am leaning toward British Green on this. My quarter, you could see the weld seam, and it looked like the old knarly weld bead before the filler went in. He dimpled the panels and welded it and just did minimal grinding before coming over it with some short hair fiberglass filler, and then Bondo. I think if you grind the weld down to where you can see and weld in bare metal, then how could you ever see it once it is coated? I am going to handle all my welds this way this go around.

[NOT A TA]

Has anyone noticed it happening more frequently where the car is exposed to rapid temperature change? I've noticed similar problems (even more exagerated) on some of my vehicles when the the vehicle is subjected to extreme temp changes. As an example, working on a car in the shop where its 70 degrees then being brought outside to below 0 temps. I thought the different expansion/contraction rates of the different thicknesses of metal and different materials (bondo etc) might be causing it.

I have one car where the paint is literaly pulling away from metal with a thin skim coat of bondo. I didn't paint the car. It had been done a while before I bought it. The problem started after I started bringing it into a heated shop from sub zero and then driving it back out into sub zero every night to work on it. I would think the same thing could happen to a lesser degree if you take a car out of a cool garage into hot direct sunlight etc. or open a heated garage in a cold climate where the garage cools rapidly till the heat catches up after the door is closed.

[scotzilla]

It is the filler shrinking over time. Basically if the filler has something to shrink into, it will. If you look at cars like the one Foose does and Rad rides, you will not see this shrinkage. Why? Because they are "metal finished". Meaning even in bare metal, you cannot see any evidence of a weld. The welds a finished perfectly smooth and even by looking at the bare metal you cant tell it was welded together. 99% of shop dont do this because it takes ALOT of skill and time. If there are no welds, how can filler shrink into them right?

ive personally blasted dozens of famous cars built by mickey galloway, leonard at dominator, brizios ect. All of them look metal finished in pics and even in person- And ALL of them get skim coated! THis is a quote from mickey himself " If its not a 1/8th inch thick you are wasting your time." This was in responce to a customer of ours complaining about 17 gal of bondo he was billed for at the shop that did his truck.

Prime example- SOme lights I did in my wagon- Check out the metal finish












still gets skim coated- Im just showing what Ive seen first hand in real life. there are several ways to get a car straight.





90% of the time when someone metal finishes a car they are taking too much material off and wear bodylines and edges dangerously thin- You really have to know what you are doing.