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85 Euro "aesthetic resuscitation" by Austin aka KilnRed

 
Old 07-11-2019, 01:51 PM
  #46  
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Originally Posted by drooman View Post
928 Roofs always seem to be prone to refinish problems.. what is the best way to seal up a preparation like the one pictured? you've got bare steel, edges of galvanization, factory sealer and primer all exposed here. how do you prevent it from blowing up in 5 years?
You are correct that the flat panels are more prone to refinish issues, though this isn't a 928-specific truth as much as it is the reality for all automobiles. The fact is the panels see the most constant rate of UV exposure. UV rays break down paint jobs by process of delamination (cohesive) rather than primer interface breakdown (adhesive).

Depending on the level of film penetration by the UV rays, the metal may or may not remain protected by OEM sealers and electrostatic coating. In the case of this 928, most of the factory protection was compromised and the evidence manifests as flaking undercoats. The required correction is removing all of the compromised undercoats. From that point, the process I prefer is machine sanding until feather edging is achieved. Before replacing undercoats can begin, it is important to have a clear understanding of the different surfaces you're working with AND the products you choose as undercoat replacements. Maximum closure and adhesion is the goal. Much of the steel is still closed in the photo'd state. For the exposed steel, chemical and mechanical etching will occur provided that the technician follows the steps outlined in any pertinent TDS sheets (cleaners, equipment setup, etc.). For the remaining surfaces, mechanical etching (sand scratches) is all that will be required BUT we still have to establish that no chemical disruption between dissimilar materials can occur or else our adhesion will be compromised. Think product compatibility.

Topcoat durability will depend on the quality of those products if all of these bases are covered and all steps for primer interface adhesion are satisfied. The issue of delamination is best combated by keeping your car out of the sun. Since the 928 is an ENTHUSIAST car, this isn't and shouldn't happen.

Choose the best clear coat available! There are many products with excellent resistance to UV penetration and I always happy to direct 928ers on these matters in their refinish endeavors irregardless of my physical involvement in the process.

FUN FACT: Clear coat delam doesn't occur as conventional wisdom might suggest in that it doesn't start with deterioration within the clear coat itself. The UV rays breakdown the base coat first. As the color deterioration worsens, then the clear coat breaks down from the base coat interface.
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Old 07-11-2019, 02:39 PM
  #47  
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Originally Posted by Kiln_Red View Post
You are correct that the flat panels are more prone to refinish issues, though this isn't a 928-specific truth as much as it is the reality for all automobiles. The fact is the panels see the most constant rate of UV exposure. UV rays break down paint jobs by process of delamination (cohesive) rather than primer interface breakdown (adhesive).

Depending on the level of film penetration by the UV rays, the metal may or may not remain protected by OEM sealers and electrostatic coating. In the case of this 928, most of the factory protection was compromised and the evidence manifests as flaking undercoats. The required correction is removing all of the compromised undercoats. From that point, the process I prefer is machine sanding until feather edging is achieved. Before replacing undercoats can begin, it is important to have a clear understanding of the different surfaces you're working with AND the products you choose as undercoat replacements. Maximum closure and adhesion is the goal. Much of the steel is still closed in the photo'd state. For the exposed steel, chemical and mechanical etching will occur provided that the technician follows the steps outlined in any pertinent TDS sheets (cleaners, equipment setup, etc.). For the remaining surfaces, mechanical etching (sand scratches) is all that will be required BUT we still have to establish that no chemical disruption between dissimilar materials can occur or else our adhesion will be compromised. Think product compatibility.

Topcoat durability will depend on the quality of those products if all of these bases are covered and all steps for primer interface adhesion are satisfied. The issue of delamination is best combated by keeping your car out of the sun. Since the 928 is an ENTHUSIAST car, this isn't and shouldn't happen.

Choose the best clear coat available! There are many products with excellent resistance to UV penetration and I always happy to direct 928ers on these matters in their refinish endeavors irregardless of my physical involvement in the process.

FUN FACT: Clear coat delam doesn't occur as conventional wisdom might suggest in that it doesn't start with deterioration within the clear coat itself. The UV rays breakdown the base coat first. As the color deterioration worsens, then the clear coat breaks down from the base coat interface.
Seems like MANY resprays result in roof, sunroof, and top of hatch issues later on from subsurface problems that were buried improperly. I appreciate your thoughtful reply, but what products have you had success with (and followed TDS to) to seal the multiple exposed surfaces left in the pics? Is there an argument to be made that once you get this far, its best to strip the entire panel to bare steel ? leaving only one surface type to get sealed properly ?

I'm just entering into this phase now On this Pearl Project
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Old 07-11-2019, 02:41 PM
  #48  
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Amazing work, and dang... what a gorgeous color!
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Old 07-11-2019, 06:48 PM
  #49  
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Originally Posted by drooman View Post
Seems like MANY resprays result in roof, sunroof, and top of hatch issues later on from subsurface problems that were buried improperly. I appreciate your thoughtful reply, but what products have you had success with (and followed TDS to) to seal the multiple exposed surfaces left in the pics? Is there an argument to be made that once you get this far, its best to strip the entire panel to bare steel ? leaving only one surface type to get sealed properly ?

I'm just entering into this phase now On this Pearl Project

I'm always careful about being too critical about the processes of others. Truth is, there are multiple proper therapies for resolving undercoat failures and I commend you for your in-depth investigation of the varying methodologies.


A bare stripped panel can absolutely be restored to a point of adequate adhesion and durability. The madness to my method is that I am going for maximum durability. Even when it means some penetration of OE corrosion protection will occur within a given panel, I still do the best I can for the remainder of that panel. Bare steel is harder to adhere to than OE undercoats or topcoats. Uniformity is the result of the new undercoat application and not a necessity beforehand with several of the BASF primers we use. The particular primer on this roof is R-M RMP27 and I have been thrilled with the results when working with this product.

Originally Posted by Kiln_Red View Post
Maximum closure and adhesion is the goal. Much of the steel is still closed in the photo'd state. For the exposed steel, CHEMICAL and mechanical etching will occur provided that the technician follows the steps outlined in any pertinent TDS sheets (cleaners, equipment setup, etc.). For the remaining surfaces, mechanical etching (sand scratches) is all that will be required BUT we still have to establish that no chemical disruption between dissimilar materials can occur or else our adhesion will be compromised.


There is another involvement in priming over bare steel.

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Old 07-20-2019, 12:37 PM
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Old 07-20-2019, 02:05 PM
  #51  
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Austin, Looks like you'll be painting many more 928's in the near future...outstanding T
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Old 07-20-2019, 02:26 PM
  #52  
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Originally Posted by 77tony View Post
Austin, Looks like you'll be painting many more 928's in the near future...outstanding T
At least a few more, God willing! I've definitely warmed to the task. In a way, it's like being bitten all over again.

One of those 928s on the chopping block is another *secret* project of my own. Not ready for the big unveil.. but it's on my radar.
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