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Refinishing the Porsche 928

 
Old 11-16-2018, 05:16 AM
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Kiln_Red
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Default Refinishing the Porsche 928

Several very recent inquiries into 928 refinish projects compelled me to touch base with 'The Shark Tank' here at RL. No better group of enthusiasts out there. As we all know, the 928 was, is, and always will be a true car enthusiast's car. On the other side of the coin from all the good that comes from the 928 hobby is the fact that we all have varying degrees of sickness attributed to the 928 addiction, as I was just discussing with another 928er yesterday evening.

Over the past year, I've had a lot of concerned 928ers make contact with fears of all types of product failure scenarios because their painter didn't do this or that.. and then they happened upon my contradictory advisement. Chief among those concerns is the issue of 'to strip or not to strip'.

If your car has been stripped to raw substrate is NOT THE END OF THE WORLD just for that fact alone. It is true that you do not want to unnecessarily remove electrostatic coatings from the 928, so the gruelling and time-consuming process of machine stripping by way of 5mm orbit dual action sander is the only way I will go because it is by only that means that I can ensure I won't penetrate e-coats.

What may or may not be known to a lot of you is that this is particularly crucial of the aluminum panels because aluminum oxidizes IMMEDIATELY. There is no escaping that truth. The only process that will ever displace and replace all contaminants with a permanent protective barrier is that of the original e-coating. This is why I say once it's gone, it's gone forever. And.. That the work of restoring a 928 should rarely or never resemble that of the efforts required to restore an old muscle car.

Additionally, I've grown quite fond of walnut media for use on stripping the polyurethane bumper covers and had not tried it until I picked up the suggestion by MrMerlin. Most 928s have too much film build on the bumpers from successive resprays. I am in the camp that says strip them. My preferred media is the walnut media.

There are too many particulars about the 928 from a structural and refinish standpoint to cover them all here and now. I am happy to help any of you in any capacity with your refinish efforts without regard to whether I am a physical participant, a help line for a DIY'er, or a tech line for your local collision repair pro to reference.

I suppose this thread could even serve as the 928 paint thread if you all want to get a working base of info started for easy reference.

Last edited by Kiln_Red; 11-17-2018 at 10:22 AM.
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Old 11-16-2018, 06:36 AM
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Hi.
I will kick it off.
I have posted a thread before asking this question however got no answers.
I am keen to fix a couple of bonnet clear coat delamination issues.
What type of paint can be used on these when painting over the original paint.
Base and clear. I am only wanting to rub back the bad areas paint over that with base and then clear the whole bonnet.
More for the learning experience more than anything. Not intending to go back to bare metal. If it only last a few years thats fine.
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Old 11-16-2018, 07:10 AM
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Sometimes delam issues are isolated, but more often the cosmetically affected areas don't reveal the true state of the paint failure. When sending, you will probably find that a feather edge won't be achieved until you go well outside the area you had originally planned. Once a feather edge is achieved, you are starting to hit material that can be topcoated. You will need a primer filler for the work area everywhere the clear coat has been penetrated and slightly beyond. After block sanding that area and final prep (at least 400 grit DA) over the entire panel, you may topcoat.

Originally Posted by grepin View Post
Hi.
I will kick it off.
I have posted a thread before asking this question however got no answers.
I am keen to fix a couple of bonnet clear coat delamination issues.
What type of paint can be used on these when painting over the original paint.
Base and clear. I am only wanting to rub back the bad areas paint over that with base and then clear the whole bonnet.
More for the learning experience more than anything. Not intending to go back to bare metal. If it only last a few years thats fine.
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Old 11-16-2018, 07:41 AM
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Great idea for a thread. I re entry picked up a really solid 86.5. Itís very straight, but a week in my detailerís shop has revealed that a lot of the panels have been resprayedó-so Iím not actually dealing with mostly original paint as implied when I bought the car. Thatís ok, it looks really good and now Iím liberated to take the car in any direction I want in the future. Iíd love to take the rub strips off. Are they just glued on or are there holes in the body under there somewhere, and would this automatically mean Iíll need a whole new spray? Thanks
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Old 11-16-2018, 12:43 PM
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Originally Posted by abrescia View Post
Great idea for a thread. I re entry picked up a really solid 86.5. Itís very straight, but a week in my detailerís shop has revealed that a lot of the panels have been resprayedó-so Iím not actually dealing with mostly original paint as implied when I bought the car. Thatís ok, it looks really good and now Iím liberated to take the car in any direction I want in the future. Iíd love to take the rub strips off. Are they just glued on or are there holes in the body under there somewhere, and would this automatically mean Iíll need a whole new spray? Thanks
there are holes for the fasteners which should be welded shut but are often just filled. since they are in the doors, fenders, and rear 1/4s touch up would require refinishing all those panels so most likely a full repaint at that point.
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Old 11-16-2018, 12:48 PM
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Deleting rub strips requires welding the holes to be done correctly. Since both sides would absolutely have to be repainted, it's a convenient time to do a full repaint.

Originally Posted by abrescia View Post
Great idea for a thread. I re entry picked up a really solid 86.5. Itís very straight, but a week in my detailerís shop has revealed that a lot of the panels have been resprayedó-so Iím not actually dealing with mostly original paint as implied when I bought the car. Thatís ok, it looks really good and now Iím liberated to take the car in any direction I want in the future. Iíd love to take the rub strips off. Are they just glued on or are there holes in the body under there somewhere, and would this automatically mean Iíll need a whole new spray? Thanks


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Old 11-16-2018, 02:36 PM
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Yep thatís what I figured thanks guys.
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Old 11-17-2018, 02:15 AM
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Looks like my question is still to be a mystery.
I will take some thinners to my car and work it out.
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Old 11-17-2018, 09:46 AM
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I suppose I must not have understood your question. Do you desire to chemically strip the part? I would suggest posting a picture of the damage here before doing anything.

Originally Posted by grepin View Post
Looks like my question is still to be a mystery.
I will take some thinners to my car and work it out.
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Old 11-17-2018, 05:47 PM
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OK. I will post pics when I can.
I just have a couple of small spots where the clear has lifted on the bonnet.
But I really just want to know what paint type is on the car or what is safe to go on the current paint.
I also have a small crack in one of the guard paint surfaces.
Thinking a sand back primer then blend of colour and full clear.
I have the full mechanicals to work through first so just want to touch up a couple of spots.
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Old 11-17-2018, 08:03 PM
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Glasurit, Spies, and Standox were the only brands that were used for all model years. Unless you have a GTS, then it is one of those brand's solventborne products. Most 928s were hand painted with Glasurit.

You can use any acrylic urethane or polyester base coat in compatibility with the paint on your car.

Good question. Sorry for misunderstanding.

Originally Posted by grepin View Post
OK. I will post pics when I can.
I just have a couple of small spots where the clear has lifted on the bonnet.
But I really just want to know what paint type is on the car or what is safe to go on the current paint.
I also have a small crack in one of the guard paint surfaces.
Thinking a sand back primer then blend of colour and full clear.
I have the full mechanicals to work through first so just want to touch up a couple of spots.
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Old 11-17-2018, 08:51 PM
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....

Last edited by Captain_Slow; 11-19-2018 at 10:51 PM.
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Old 11-17-2018, 08:54 PM
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Originally Posted by Kiln_Red View Post
Glasurit, Spies, and Standox were the only brands that were used for all model years. Unless you have a GTS, then it is one of those brand's solventborne products. Most 928s were hand painted with Glasurit.


Great thread and looking forward to the information that comes from this one... This will help quite a few of us that are looking at long term ownership.

Above, you say "Unless you have a GTS"... What is the difference in the GTS paint and what precautions should GTS owners be aware of?

Was it a running change and does it affect the 90 - 91 GT's?

Thanks in advance!

Dave

Last edited by 928 GT R; 11-17-2018 at 11:35 PM.
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Old 11-17-2018, 10:01 PM
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Originally Posted by grepin View Post
OK. I will post pics when I can.
I just have a couple of small spots where the clear has lifted on the bonnet.
But I really just want to know what paint type is on the car or what is safe to go on the current paint.
I also have a small crack in one of the guard paint surfaces.
Thinking a sand back primer then blend of colour and full clear.
I have the full mechanicals to work through first so just want to touch up a couple of spots.
lets be clear (sorry...) that there’s no safe and durable way just spot-spray some clear over the exposed under color layer once that’s been breached. The guidance you are receiving includes sanding back to a firm good layer, feathering, then primer sealer before new color and clear for the whole section. On your year, only metallics had clear fro the factory. Repairs are often two-stage, and it’s a guessing game what they used.
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Old 11-18-2018, 12:49 AM
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Originally Posted by dr bob View Post


lets be clear (sorry...) that there’s no safe and durable way just spot-spray some clear over the exposed under color layer once that’s been breached. The guidance you are receiving includes sanding back to a firm good layer, feathering, then primer sealer before new color and clear for the whole section. On your year, only metallics had clear fro the factory. Repairs are often two-stage, and it’s a guessing game what they used.
Yes, absolutely. Sorry. This was precisely my suggestion and you are correct. Spot clearing is refinishing blasphemy.

If you'll refer to my avatar picture, I elected to not refinish the door jambs on my own car. I have the means to not leave a tape edge of course. That said there were delam issues along the insides of the fenders in the engine bay, so I removed the hood to get a nice tapeless job there.

Some GTSs had Glasurit 90-line (waterborne) base coat. There is no particular concern with regard to quality or durability. It is a fine product too. The other paint manufacturers did not have the technology until '94, but none of their OE contracts were waterborne. Something that may be noteworthy with 90-line is that it is not truly a waterborne. It is what's known as a "hybrid" product.

Refinishers need to be aware of two things with regard to original paint. Many of the earliest 928s shot with S/H Permacron need to ID it. The easiest way to do so is to become familiar with the smell. I would discourage anyone not using a polyester base coat to prime and/or seal over the original Permacron or large scale issues with regard to wrinkling and adhesion may occur. The problem is that today's acrylic urethanes are formulated much "hotter", thus the solvents easily penetrate the original paint and then "reverse" its composition from its solid state. The second helpful tip is that spraying solventborne paint over exposed 90-line base on a GTS is a big NO NO! I accidentally did this myself. A terrible paint edge will emerge after clear that will worsen over time.

I once tried to catalogue original paint brand by undercoat colors, but this proved to not be a fault proof system. Some of you may be shocked to know this, but Porsche and others actually contracted undercoats and topcoats out to different paint companies sometimes. For example, your car could have Standox primers/sealers with Glasurit base and clear.

Last edited by Kiln_Red; 11-21-2018 at 03:47 AM.
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