Paint problem to solve

[Discseven]

Going to strip & paint my car. Before getting on with it, have a look at this…



Was last painted by a shop around 2005. Front hood (seen above) was done again in 2012 because the paint was pulling up from the crevices that lead to the fresh air intake.) That work was done by a different shop. Fresh, all the paint on both occasions looked great. Over time, what you see above has increased in appearance in different areas around the entire car. Before the hood was redone, there was just a faint appearance of what's seen in the photo above. I discussed it with the "redo" shop and their response was to apply a coat of zinc chromate. Hood sat for a few days then they sanded the zinc chromate off. Then primed and painted the hood to a good looking finish. Eventually what you see now arose in a very slow progression over years. As it is, this looks just like the first hint of it at the very beginning only now it's more spread out and more pronounced. Occurs to me as I write this that the issue is (EDIT) mostly on the up facing areas of the car---front hood, read hood and tops of the rear quarters. t is only on the driver's rear qtr panel side. No painted roof / Targa. The car is parked indoors so sunlight would seem a minor player.

Of course I don’t want to start redoing the car before knowing what's happening and more importantly, how to quench it so there's no resurfacing.

[Marine Blue]

Any idea of there’s filler under that section that perhaps is gassing off or deteriorating and resulting in the paint issues?

[Discseven]

Originally Posted by Marine Blue

Any idea of there’s filler under that section that perhaps is gassing off or deteriorating and resulting in the paint issues?

When the car was originally worked on, I saw nothing of it during the progress. I did see the hood in progress for the redo...









On the hood, "issue area" is at the passenger's side roughly midway between the front and rear of it.

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[Dpmulvan]

It’s an adhesion problem caused by incompatible product, improper flash times and or too high humidity. Just my two cents, be worth a shot finding out what primers and other product were used. Outgassing usually results in tiny bubbles that look like fisheyes.

[Discseven]

Originally Posted by Dpmulvan

It’s an adhesion problem caused by incompatible product, improper flash times and or too high humidity. Just my two cents, be worth a shot finding out what primers and other product were used. Outgassing usually results in tiny bubbles that look like fisheyes.

I know for a fact that both the entire car and the hood were shot in ambient air. So plenty of moisture (Miami.) I did not leave either paint shop on good terms---both shops offered me one can of crap or another so am not going back now even if they invited me. I'd go into details but it's meaningless to the question in hand. That said DP, thank you for the suggestion.

Appearance here reminds me of a skin rash.

If I'm not mistaken, Porsche galvanized car metal sometime prior to '80. Would bare metal not flash rust due to galvanizing? Or would it? I have no idea how long either shop gave to considering how quickly to coat the bare metal. In retrospect, I do not see either shop being very mindful of expert practices.

What's tricky here is that the defect appears the same in the paint for the work done by both shops. It's possible they both screwed up prep & application in a similar manner. If that is the problem here, great! What I worry about is the issue being in the metal.
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[962porsche]

galvanized coating when a panel is stripped to bare in most every case your removing it or a good part of it from the car. not a big deal as all cars now a days are galvanized coated. replacing it with a chromated primer is what you do. if you think for one second that the galvanized coating is the end all to stop rust think again. it's more to protect the areas between the panels and that's the intent of it's uses to simply protect places like the areas of the inner rockers just to make them last a bit longer that if they were not galvanized dipped.
like I said as soon as you start to sand the top surfaces of a panel it's getting sanded off or so thin having it does nothing any more.

as for what your seeing my guess is that it's from oily hand prints.
being on the top surfaces is where some lazy ass was leaning on the car with one hand and sanding it with the other.
to know for sure I would have to sand off what it there little by little sanding thru each layer.
most everyone will wear gloves to protect themselves but not the car. when it's hot and your sweating from working where is your oily sweat going as your leaning on the car.
your oily sweat doesn't wash off it just gets sanded into the panel.
even when you wipe down the car to paint it it's to late the oils from your hand have been sanded into the panels and spread around from sanding.

[Discseven]

Originally Posted by 962porsche

galvanized coating when a panel is stripped to bare in most every case your removing it or a good part of it from the car. not a big deal as all cars now a days are galvanized coated. replacing it with a chromated primer is what you do. if you think for one second that the galvanized coating is the end all to stop rust think again. it's more to protect the areas between the panels and that's the intent of it's uses to simply protect places like the areas of the inner rockers just to make them last a bit longer that if they were not galvanized dipped.
like I said as soon as you start to sand the top surfaces of a panel it's getting sanded off or so thin having it does nothing any more.

as for what your seeing my guess is that it's from oily hand prints.
being on the top surfaces is where some lazy ass was leaning on the car with one hand and sanding it with the other.
to know for sure I would have to sand off what it there little by little sanding thru each layer.
most everyone will wear gloves to protect themselves but not the car. when it's hot and your sweating from working where is your oily sweat going as your leaning on the car.
your oily sweat doesn't wash off it just gets sanded into the panel.
even when you wipe down the car to paint it it's to late the oils from your hand have been sanded into the panels and spread around from sanding.

Thanks for the input 962. The reacted paint is all over the place. Mainly the front hood and rear quarter panels. And not small areas. Rather wide spread. If this is personal touch contamination, the paint guys were absolute slobs.

Been advised to sand the metal and apply 2 coats of epoxy primer. And not apply any metal treatment. Is that a sensible approach to this?

[962porsche]

my guess as to just being from some slob is just that a guess. it is a common thing that happens when people working on cars don't protect the car by wearing gloves.
it could be surface rust coming up too?

yes it will need to be stripped to bare metal! than a good quality epoxy primer needs to be sprayed down.
metal treatments in most cases are not needed.
it's a good idea to only open up to the bare metal an area that you can get primer back on in that days labor.

[Discseven]

Originally Posted by 962porsche

my guess as to just being from some slob is just that a guess. it is a common thing that happens when people working on cars don't protect the car by wearing gloves.
it could be surface rust coming up too?

yes it will need to be stripped to bare metal! than a good quality epoxy primer needs to be sprayed down.
metal treatments in most cases are not needed.
it's a good idea to only open up to the bare metal an area that you can get primer back on in that days labor.

...Then I'll plan on doing panels one at a time. Is there any need to top coat the epoxy primer immediately?

[962porsche]

no need to get top coat in over the epoxy primer right away.
this doesn't mean you can let cars sit in primer for a long ass time. primers are not a real good moisture barrier. it will protect the metal from rusting to a point for a few months but it's not like you can leave a car with primer on it out in the rain or even in humid weather for long periods or moisture will leach it's way thru the primer.

[Discseven]

Originally Posted by 962porsche

no need to get top coat in over the epoxy primer right away.
this doesn't mean you can let cars sit in primer for a long ass time. primers are not a real good moisture barrier. it will protect the metal from rusting to a point for a few months but it's not like you can leave a car with primer on it out in the rain or even in humid weather for long periods or moisture will leach it's way thru the primer.

Thank you 962

[rowingone]

Paint problems like this are usually due to unclean surfaces or improper product compatibility or application. Any good shop would have a system from bare metal to top coat that he knows is compatible and always uses the same routine. I would also recommend a primer sealer just before top coats are applied. You need to pay the money to someone that knows what he is doing . . knowledge costs money but a good paint job from bare metal to final buff out is in the $15-20K range. I suspect you are using the cheaper alternatives because problems like these are not at all common with respected painters.

[Discseven]

Originally Posted by rowingone

Paint problems like this are usually due to unclean surfaces or improper product compatibility or application. Any good shop would have a system from bare metal to top coat that he knows is compatible and always uses the same routine. I would also recommend a primer sealer just before top coats are applied. You need to pay the money to someone that knows what he is doing . . knowledge costs money but a good paint job from bare metal to final buff out is in the $15-20K range. I suspect you are using the cheaper alternatives because problems like these are not at all common with respected painters.

Thank you ROW. I did not go to a top of the line place for this hood job. Intentionally so to see if they would produce good results. They did a door for me that has lasted quite well and that job looked good so I gave them this hood to do. There was a considerable gap between these jobs. Point being, management and processes change. And so the outcomes.

[ChrisHamilton]

Looking at it from the perspective of one who does this for a living, it sorta looks like where a spray can type primer was used and the solvent in the subsequent coats lifted it. But that would generally occur right away. When a shop says zinc chromate primer that always means to me the 1K stuff in a spray can which is not what you want to use. For many reasons.

If the hood was aluminum it would make more sense as that looks similar to the corrosion you sometimes see when Al is contaminated with steel. Intergranular corrosion from sanding lead with aluminum oxide paper looks like that as well. Highly doubt though that there was lead used as filler on your car.
Could it be contamination from hands or otherwise? Possible but generally that starts out looking bad and doesn't get progressively worse. I've never seen where long term oils/contamination on the panel does that. Even if it gets on there a proper wipe down with the correct W&G remover will take care of it. Except for filler panels don't really sponge up contamination. At least that has been my observation over the years.

So what could it be? My guess is that the hood was prepped/sanded and there was bare metal poking through in places on the hood after sanding. Typical. But because they were rushing it, they did not reprime. Depending on the primer used, even if it is thin but covering in an area it can rust underneath. That typically happens with 2K urethane primers shot directly over bare metal. That's what it looks like in the pics. More than likely those areas got a slight amount of surface rust on them from sitting in a humid climate, probably waiting a day or two after prep to get painted, which did not get removed before being sealed as the car got color. More than likely happened on the first repaint and wasn't fixed on the second. Only sanded and primed over. Over time it would progressively worsen. I would bet money that if you stripped it with heat and a razor blade there, underneath you would see surface rust in that area.

To fix it, strip it to metal. Ensure no surface or pit rust remains. Apply a quality epoxy primer and proceed. Forget this zinc chromate BS. No one I know uses it. A quality epoxy primer is the best thing you can apply to bare metal. There are a multitude of ways to screw up so if you are doing this yourself be sure to read the TDS of the product you are using and follow it to a "T". If you are looking for a good epoxy primer, SPI EPoxy is the best I've used.

[ChrisHamilton]

I'll add if you do this yourself and decide to use epoxy primer, be careful using the various acid metal treatments out there. Epoxy does not like or bond to an acid film. So if you use a metal treatment (no reason to on that hood IMO) you need to ensure that the acid film is "neutralized" or more correctly removed. Never trust the manufacturers of the various products claims that their product can be painted over. Maybe with paint from the 1960's but with what is used today no way. Always do as the paint manufacturer recommends.

Example, Ospho is a popular phosphoric acid treatment. If applied and left to dry it leaves an acid film. Completely normal and necessary to ensure that rust is removed. But if epoxy is applied over that it will not adhere correctly. Most of the time it will peel right off after the epoxy sets up. So before applying epoxy you need to "neutralize" it. Technically not the correct description but close enough. So to neutralize the acid film, you simply re-wet with the product, in this case Ospho, and keep it wet for 10-15 minutes. Taking care not to let it dry out. Good idea at this time to scrub with a wire brush any crustiness that gets left after the process. So wet it, keep it wet with the product, don't let it dry. Keep wetting it down with the product if necessary. After 10-15 minutes rinse well with water. Blow off quickly. Panel is now neutralized and ready for epoxy or additional sanding to prep the panel (80 grit on a DA to ensure mechanical adhesion).

You can't sand an acid film off either. It will remain in the microscopic pores of the metal and cause failure. Only options are as I described above or media blasting.

[pottsalot]

Haven't seen crazing like that since cellulose days!

Chris is spot on! Good info from an experienced body man. Do what you enjoy doing.

[Discseven]

Originally Posted by ChrisHamilton

Looking at it from the perspective of one who does this for a living, it sorta looks like where a spray can type primer was used and the solvent in the subsequent coats lifted it. But that would generally occur right away. When a shop says zinc chromate primer that always means to me the 1K stuff in a spray can which is not what you want to use. For many reasons.

If the hood was aluminum it would make more sense as that looks similar to the corrosion you sometimes see when Al is contaminated with steel. Intergranular corrosion from sanding lead with aluminum oxide paper looks like that as well. Highly doubt though that there was lead used as filler on your car.
Could it be contamination from hands or otherwise? Possible but generally that starts out looking bad and doesn't get progressively worse. I've never seen where long term oils/contamination on the panel does that. Even if it gets on there a proper wipe down with the correct W&G remover will take care of it. Except for filler panels don't really sponge up contamination. At least that has been my observation over the years.

So what could it be? My guess is that the hood was prepped/sanded and there was bare metal poking through in places on the hood after sanding. Typical. But because they were rushing it, they did not reprime. Depending on the primer used, even if it is thin but covering in an area it can rust underneath. That typically happens with 2K urethane primers shot directly over bare metal. That's what it looks like in the pics. More than likely those areas got a slight amount of surface rust on them from sitting in a humid climate, probably waiting a day or two after prep to get painted, which did not get removed before being sealed as the car got color. More than likely happened on the first repaint and wasn't fixed on the second. Only sanded and primed over. Over time it would progressively worsen. I would bet money that if you stripped it with heat and a razor blade there, underneath you would see surface rust in that area.

To fix it, strip it to metal. Ensure no surface or pit rust remains. Apply a quality epoxy primer and proceed. Forget this zinc chromate BS. No one I know uses it. A quality epoxy primer is the best thing you can apply to bare metal. There are a multitude of ways to screw up so if you are doing this yourself be sure to read the TDS of the product you are using and follow it to a "T". If you are looking for a good epoxy primer, SPI EPoxy is the best I've used.

Originally Posted by ChrisHamilton

I'll add if you do this yourself and decide to use epoxy primer, be careful using the various acid metal treatments out there. Epoxy does not like or bond to an acid film. So if you use a metal treatment (no reason to on that hood IMO) you need to ensure that the acid film is "neutralized" or more correctly removed. Never trust the manufacturers of the various products claims that their product can be painted over. Maybe with paint from the 1960's but with what is used today no way. Always do as the paint manufacturer recommends.

Example, Ospho is a popular phosphoric acid treatment. If applied and left to dry it leaves an acid film. Completely normal and necessary to ensure that rust is removed. But if epoxy is applied over that it will not adhere correctly. Most of the time it will peel right off after the epoxy sets up. So before applying epoxy you need to "neutralize" it. Technically not the correct description but close enough. So to neutralize the acid film, you simply re-wet with the product, in this case Ospho, and keep it wet for 10-15 minutes. Taking care not to let it dry out. Good idea at this time to scrub with a wire brush any crustiness that gets left after the process. So wet it, keep it wet with the product, don't let it dry. Keep wetting it down with the product if necessary. After 10-15 minutes rinse well with water. Blow off quickly. Panel is now neutralized and ready for epoxy or additional sanding to prep the panel (80 grit on a DA to ensure mechanical adhesion).

You can't sand an acid film off either. It will remain in the microscopic pores of the metal and cause failure. Only options are as I described above or media blasting.

Chris, thank you for the detailed perspective and guidance. Am tempted to razor blade a section off as you suggest. Should I dive in, I'll post what is found.

With no work area to speak of to paint the car, I've considered how it might be done one panel at a time at the marina parking lot where I do mechanical maintenance to the car. (Living in a condo, I can only get away with so much in the resident garage.) I've painted a small section of the car on one occasion at the marina. 2k epoxy primer on the bare metal followed by 2k paint. Ok but not perfect. Whether I have the gumption to take on a repaint of the entire car... stripping it to bare metal... no small project.