My Son and I have been working on this 72 chevelle SS for 2 years. it is his first car. We fixed the rust spots and dents and primed it with PPG's NCP 280 and sealed it with PPG's DP90 after the 280 cured for about 3 months. The car looks nice and strait. We have been having some hot days latley and I noticed that where the rear quarter panel meets the roof there was a perfectly strait blister in the paint right along this factory body seam from the rear window to the rear windshield. The blister is about 3/16" wide and comes up about 1/16 of an inch. It has to be in direct sunlight to come up, and if you put the car in the shade or wipe it with a wet rag, it totaly disapears until it gets hot again. I sanded it down to the filler and re-primed it. It came up a second time (by the way both sides of the car are doing this exactly the same). I took it down to the OEM seam/body filler and totaly removed the filler down to the spot welds, replacing it with Dynatrons Dyna-Glass short strand fiberglass filler. I sanded that with 60 grit paper and applied a thin coat of 3M Light Weight Body Filler. I sanded the filler, and r-eprimed it, let it sit for a week and put the car out in the sun. The damn lines came back! Both sides! I am at a loss on what to do. The head liner and rear windshield are in and to weld metal plates or lead the seams would ruin them, as well as distort the hell out of the cars top. The car was originaly a vinyl top car and plastic filler is what it had in the seams. Anyone have any ideas? I sure want my kid to be able to drive his car during his Senior year(thats this year). Any help would be so appreciated. And to make it even worse we are painting it black smile.gif

I have had some nightmares with lead seams myself. Since you removed the lead(good idea). I would sand blast the area clean,with a small spot blaster, fill it with a fiberglass filler like duralglass finish it with regular filler,then three good coats of epoxy primer. Make sure you mix the filler well,i have had bubbling with filler that wasn't mixed with the hardner good enough.

I have taken it down and reprimed it three times with the same problem coming back, think I should skip the sanding primer and just go with the epoxy on those areas?

Did you pop the blister and see what it was. Water? Air?

Just air. It looked like the topcoat (epoxy primer) and the sanding primer, along with the thin coat of bodyfiller lifted off of the OEM filer in the seam, I have not taken off the third attemp yet to see, but it is strange just how perfectly strait the thin blisters are. Like someone placed a piece of string under the paint.

When you say you have spot welds there, this means you have overlapping panels. In turn, this means you now have to deal with thermal expansion rates...... :mad:

Welds are typically more brittle than the surrounding metal, thus the coefficient of thermal expansion is different for the different areas (meaning they won't expand as much). Is this line right at the edge of the overlap, possibly curling up?

When you hit it with the wet rag, everything shrinks back, along with the internal stresses.

The body experts should probably answer for the fix, but I believe you would really have to get rid of the overlap joint and butt weld, along with using a hammer and dolly while grinding down the welds, to keep the metal from shrinking up.

Crankshaft

Am not excatly for sure about the ncp 280, you sure thats the number as they make a 272(greenish) and 250(kinda purple)?

Anyway we tried the ncp272 as a primer surfacer used 2 gallons of the stuff. Noticed when wetsanded if you used a good amount of water while wetsanding the 272 would absorb some of that water. Only later after the clear was applied would the water come back up forming a REAL TRICK LOOKING BLISTER smile.gif

Are you wetsanding this ncp 280 primer or dry sanding before you apply the epoxy?

You say the filler lifted also from the metal?
Did you apply any metal treatments to the bare metal first? As appling filler over these treatments and etch primer can cause the filler to lift. How did you clean the factory seem, are you positive you removed all containments?

Also something to note. Am not sure if PPG has since corrected this problem but when the DPLF epoxy primer replaced the DP, PPG released a tech bullention that mentioned that DPLF needs to be topcoated the same working day the epoxy is sprayed or lifting can occur.

But after re-reading your post a few times I dont see how any paint product or user fault is the problem. My guess is that you have sometype of containment in the leaded area that you failed to remove or you applied some type of metal treatment on the metal before hand.

this seam is a factory seam where the rear quarter panel and roof attach. The seam is about12" long, 1/2"-5/8" wide and steps down about 5/16" below the finished surface where the two pieces are spot welded (like a rectangular trough). there is no surface lap like you are thinking, it is well below the surface. I really appreciate the response, thanks

We did wet sand the NCP 280, but the car sat for at least three weeks in summer weather before we shot the DP90 on. There was never lead in this seam it was some kind of OEM bondo like filler that we replaced with good stuff. The whole body was cleaned with surface Technology's Metal Prep 79.

oops forgot to say thanks
Thanks

The problem is coming from the factory seem right? that seem has overlapping metal about 1/2-3/4in of metal. You might have some type of containment leaking out of the seem casuing your paint/filler to lift. This is times a common problem with cars that have been chem dipped as later on the chemicals start to leak out of the factory seems.

Also what excalty is this surface technology's metal prep 79? Never heard of it. Is it like a wax and grease remover simliar to PPG's dx330 that is designed to remove slight amounts of oils and dirt before painting? Or is it like an acid wash product like POR15 Metal Ready that etches the metal prior to topcoating? As stated before filler doesnt mix over etch products. When filler is applied over etch the filler can lift due to chemical reactions that dont get along.

Once again how did you clean the area? Simply grinding is not enough on those leaded seems. As someone could have replaced the lead with filler years ago?? Just a guess

Welding plates in or adding lead back in is NOT the answer. If the problem is lifting the filler from the metal then its something inbetween the filler and metal. Oil from the air tools, hands, not cleaning the metal properly with a wax and grease remover, your metal prep 79???

I would find out what that stuff is made of...Eric

The Metalprep is a solution you dilute with water and wash the metal down before painting. It does remove rust if you scrub it long enough. I think it is some kind of mild acid. However the label says the stuff is for preparing metals for paint. The Directions are to wash down the surface with the solution snd rinse with water, dry, and paint. My neighbor who does quite a bit of bodywork is who suggested what products I should use. That does not mean it is not what you are tryig to explain, maybe I should try tearing it off for a fourth time :( , I just want to be sure it is the last time I have to do it. Thanks

Iam willing to bet that metal prep is your problem. That type of prep is a acid based product that cleans and etches the metal prior to topcoat. PGG's dx579/dx520 would be similar products. A wash or etch primer is just a sprayable version of this system, like PPG dx1791.

When you apply filler over etch products, when the filler is curing it overgoes a chemical reaction this reaction reacts with the acids in the etch causing the filler to lift from the metal.

Since you applied this product to the car with water then again more water to remove/clean it from the metal my bet is that some got in behind that factory seem and is leaking out thus causing your filler lifting from the metal in turn gives you that line.

Maybe the heat accerlates(sp?) the chemical making it leak out from the seem, as when you put it outside the line shows. I know a few cars that have been chem dipped, some the chemicals leak out after they have been caught in a rain, never when washing only in the rain :confused: :confused: One has been dipped over 10 years ago and still leaks, ever hurts the paint but produces a whitish dry salt looking powder.

I just dont see any other thing that could cause this expect the metal prep 79 you used...Eric

well, I have attempted to repair this thing for the 4th time and the lines still raise in direct sun. I have spent most of the summer trying to get this taken care of. I am just stumped.

Mario

Try removing the filler .Then grind or blast the seem clean. Apply a good etch primer (SEM makes a spray bomb). Apply the epoxy primer,Put your filler over the epoxy.
You said the rear glass is in the car. You may have a leak in the window chanel seam.This would allow moisture to get into the joint.
Using a spary bottle apply soapy water around the area. From inside blow compresed air around the seam.If its leaking you'll konw it.

Sounds like a problem I had one time when I was shooting "too wet"

this car has not seen the road yet since we bought it. The rear windshield is a new instalation, and the car has been garaged. I have ground the metal clean, but have not tried sealing the metal before I put the filler in. Maybe that will make some kind of difference. I have been told the only way to fix it will be to put lead in that seam. Nobody does lead in my area :( . Im starting to think that since the filler in the seam is so much thicker than any where else (about 1/4 - 5/16 thick) that it will expand more from the heat than in the other areas. There might be nothing I can do but lead. I was also thinking of some kind of epoxy filler.
Thanks for the response, I am still looking at them.

Mario

Have you tried cleaning the metal,then using epoxy prime,then filler on top of that?

Evercoat makes a body filler that uses aluminum powder insted of talc. Thay call it "Metal-2-Metal" part# fe889.
web page (http://www.ketone.com)

Sorry but I really dont think lead is the answer. Lead can cause just as much problems if not more if not used right!!! Am sorry but I guess I just dont understand the LEAD is the auto body cure all for all that ails :confused:

I would remove the glass so you get FULL access to the metal. Then seal the metal with an epoxy primer like DPLF mixed with 402. Apply two coats allow to cure for 2 days then come back with some 180 grit and just light scuff up the epoxy. No need to go crazy just enough to give it some tooth. Since you are afraid of expanding filler then apply some fiberglass straided filler like USC's marglass or duraglass whatever they call it. Theres a good one also, even the 3M rep just told me this on monday, that UPOL's fiberglass filler is the best on the market called fiberall

The fiberglass filler is somewhat stronger because of the fiber straids in the filler. Apply that fiberglass filler for a base filler then topcaot with Rage or Rage gold to smooth out since the fiberglass filler can be somewhat hard to feather out.

i give a thumbs up to fiberall also, it is awesome they use this stuff underwater to patch boats, very strong stuff, upol uses european resins they claim which are alot better, i would bring it to bare metal fiberall it, then feather out with rage then urethane prime it, and you should be all set, goodluck
jake