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Refinishing the Porsche 928

 
Old 11-18-2018, 01:54 AM
  #16  
Kiln_Red
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I should add that I have not personally seen a 928 GT with a factory waterborne basecoat, but I have been told that a few exist. I am inclined to think this is incorrect as I don't know of any '92 GTs. BASF, Glasurit's parent brand, did not offer 90-line until MY92 for sale to OEs or to auto paint distributors.
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Old 11-18-2018, 11:51 PM
  #17  
hernanca

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Default Good examples of bad paint

Here are the pictures I couldn't figure out how to attach to IM. Putting in this thread to serve two purposes: 1) so you can see what I want to correct on my white 86.5 and 2) give some on-topic examples of what a bad partial respray can look like. This:






is what the right rear quarter and part of the right door looked like when I bought It in 1999.

The bad I can see is the mismatch of gran prix white paints ("pre-race GPW" (mine) vs "post-race GPW" respray color?), the peeling/cracking at edges, and the overspray from lack of trim removal.

What I dont understand is the deep cross-hatch lines seen in the lighting reflection areas and the spotting (which I haven't been able to clean off).

Feel free to reference these as examples of a bad partial respray
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Old 11-19-2018, 12:35 PM
  #18  
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Hernanca --

The lines are pre-spray prep that wasn't done. You are missing a couple layers of primer-surfacer, three sheets of 400 wet-or-dry, three quarts of elbow grease, and more. A sealer coat somewhere in the mix would have helped with the color bleed, and certainly cut down on the checking in the new top layers. Looks like a rattle-can spot repair to me, with lacquer or other low-boiling solvent paint over damaged original paint.
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Old 11-19-2018, 01:39 PM
  #19  
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All that "paint" needs to come off .Trying to cover it up will not end well.
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Old 11-19-2018, 08:41 PM
  #20  
hernanca

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Thank you, Dr Bob and Jim. The plan is to "correct it", whatever that might entail. The rest of the car has original paint, so I would like to preserve that if at all possible.
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Old 11-20-2018, 12:25 AM
  #21  
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Originally Posted by dr bob View Post
Looks like a rattle-can spot repair to me, with lacquer or other low-boiling solvent paint over damaged original paint.
This is absolutely correct. Top shelf urethane products don't behave that way. Some people refer to that as "crow's feet". This is a paint issue that should have died by the mid 80s along with the lacquer era. As you were already aware, someone did a quickie cheap job using really sorry product.

Also, the advice that every bit of that paint needs to come off is absolutely correct to achieve a quality, durable finish.

Last edited by Kiln_Red; 11-21-2018 at 03:45 AM.
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Old 11-20-2018, 07:23 PM
  #22  
hernanca

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Originally Posted by Kiln_Red View Post
Also, the advise that every bit of that paint needs to come off is absolutely correct to achieve a quality, durable finish.
Thank you.

But only the paint layer, as described above, and since the door's outer shell is aluminum (vs. the rear quarter's galvanized steel), this is especially important for the door, correct? That is, keep any original factory layers if possible?
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Old 11-21-2018, 03:44 AM
  #23  
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Originally Posted by hernanca View Post
Thank you.

But only the paint layer, as described above, and since the door's outer shell is aluminum (vs. the rear quarter's galvanized steel), this is especially important for the door, correct? That is, keep any original factory layers if possible?
Right. Sometimes it is unavoidable to penetrate original undercoats to make a repair. The idea with the 928 and other cars of comparable quality is that less is more in this sense. There are no improvements to be made by removing the original undercoats. In fact, it is counterintuitive as there is no way (economically) to even match the original quality. And, yes, this is more critical with aluminum as it oxidizes immediately. Even staying inside the 15 minute window from final prep to epoxy won't come close to offer the protection of electrostatic coating, but it's the best we can do when and where necessary.
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Old 11-21-2018, 10:50 AM
  #24  
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Originally Posted by Kiln_Red View Post
Right. Sometimes it is unavoidable to penetrate original undercoats to make a repair. The idea with the 928 and other cars of comparable quality is that less is more in this sense. There are no improvements to be made by removing the original undercoats. In fact, it is counterintuitive as there is no way (economically) to even match the original quality. And, yes, this is more critical with aluminum as it oxidizes immediately. Even staying inside the 15 minute window from final prep to epoxy won't come close to offer the protection of electrostatic coating, but it's the best we can do when and where necessary.
Thank you, everyone - very helpful!
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Old 02-13-2019, 01:47 PM
  #25  
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I jumped into the paint tank

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Old 02-13-2019, 03:45 PM
  #26  
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Ambitious. After having painted 5 cars, I gave up on DIY for paint work. I'll strip bumpers, trim, and do a bit of sanding prep, but after that it goes to the paint shop. They have the tools and skills to get it back right without do-overs three or four times. I painted my Matra, only to go back and do it over twice. Once completed, it look fantastic for about 2 years. Paint shops justify every dollar of the cost.
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Old 02-13-2019, 04:54 PM
  #27  
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^^^ What Doc said ^^^

Looking at Brad's debris field from chem stripping brings back the nightmares. I'm maybe 50-50 on "successful" DIY paint jobs. There are some, like old British cars, where you can justify DIY because paint shops won't or can't shoot the original products anymore. Unless you are building a car for Pebble or Amelia Island shows, it's not a challenge to get the original effect with poorly-applied modern products. Lasts longer too. Back to the question though -- does it make sense for the average person to prep and paint their own cars? No.

OK if you want to do the disassembly and reassembly stuff so you know it will be done. Know that the removed pieces will take up the workshop space equivalent to the whole car. If you plan on doing work on the removed bits, that takes more space. Know that your painting contractor will have the car for at least 4x the time you agree on if you allow it, so schedule and budget accordingly. Coordinate with the painter before you start taking anything apart, so that you are all playing to the same goal.
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Old 02-14-2019, 10:24 AM
  #28  
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Great thread!

What's the consensus on plastic bead blasting? I have a facility near me that has a plastic room big enough to do helicopter bodies and small plane wings and fuselages. The guy says he can blast the paint off an aluminum coke can and not degrade the metal, as is apparently required by the FAA / NTSB to do aircraft work. He plastic blasted my friends 911 chassis down to the galvanizing. the results were really nice. On my car #24 (originally red) there are many layers of craptastic paint.. some black rock hard coating, original primer (grey) original paint (red) yellow primer, army green, gray primer, purple. The plastic blaster says he can leave original primer (says its rock hard stuff anyway) or go to the galvanizing. Given the choice, what are the best procedures/ products to build on to the original galvanizing, or original primer?

While we're at it, Since it is 1977 non metallic color I'm assuming it was single stage from the factory? Many modern painters don't want to mess with that and are more comfortable with base/clear. I've also heard (but can't confirm) that Glasurit paint is superior to other brands especially with rich bright colors... Urban Myth?


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Old 02-14-2019, 10:48 PM
  #29  
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Default Dry Ice Blasting aka C02 blasting

"Dry ice blasting is an invaluable commercial cleaning service for restoring damage from fire, mold and the restoration of historical artifacts. It is up to three times as fast as other methods of cleaning and is so non-abrasive that it can even be safe to remove rust, grime and corrosion on delicate and valuable historical artifacts."
Claim it can take paint off wood with zero effect to woodgrain.
A thought
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Old 02-14-2019, 11:34 PM
  #30  
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Droo-

There's a lot of forgiveness with base-clear systems compared with original single stage. The supply of folks still competent with original paint systems is shrinking fast. Plus since you build all the prep based on the final stages, you'll want to line up the talent and products/system before you take even the first steps beyond stripping and e-coating.

------

Local PCA held a concourse paint prep clinic last weekend. I sat quiet for the first 30 mins, asked a couple questions, had to leave after hearing the answers. There are a lot of opinions on this stuff out there. Do your own homework and identify the resources you have available. Lots of bs.
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