Intermezzo said:
Furthermore, DavidB is a person who's advice I highly respect and he's also been a strong advocate of the layering ability of certain paint sealants.
Oh, jeeze... did you have to bring me in to this?
Personally, I laugh at many of the things people try and recommend. So, here's my official position:
1. Some sealants containing cleaners have the ability to significantly improve the finish quality and durability by applying two coats. I chaulk this up to the simple fact that the first application is really acting as a pre-wax cleaner and the second application has a nice, clean surface giving it a better chance of "sticktion". Anyone who has applied back to back coats of Klasse AIO will know exactly what I'm talking about.
2. I don't believe any sealant will provide an improved visual impact beyond 3-4 coats. The very nature of chemical film technology will simply not allow it unless the base formula is inert. Once you introduce a solvent and mechanical action, you will remove some, if not all, of the previous coating. I know of only two systems that fall into the "remove some" category. All others I've tested remove all. Zaino Z5 has a low enough solvent content that it will not remove itself. Klasse SG has no solvents at all. Everything else, I'm sorry to say, falls in to the "removes itself" category. This is not to say that applying two coats of NXT, BF, AIO or UPP will not improve the final finish... it will... but not past two coats.
3. Layering of AIO, SG and a wax like P21S or Pinnacle Souveran works because you are applying different chemical foundations on top of one another. Once Klasse SG cures, the low solvent content in Souveran will not hurt the acrylic film. The look improves becuase the acrylic molecules are small and even in size and the wax molecules are long and stand up vertically. This gives the visual appeal of more depth. I have tried layering waxes on petrol-based polymer sealants and concluded it does not work. Even with Zaino Z2+ZFX, I applied Souveran after a 24 hour cure period, then washed with Z7 and the Z2 finish was gone. The solvent in the wax removed the Z.
So, my official conclusion is:
* Any sealant containing solvents/clay can be applied twice to get a better finish. If you want to call this "layering", okay, but they don't.
* Unlike products may be able to be layered if they are chemically compatible. Z2 on top of Z5 is an example. KSG on top of AIO is another example.
The results anyone gets from surface care products vary widely based on the process, ancillary products and conditions. I can make a product like NXT last for months and continue to look great by using the right car wash, detailing spray and toweling. Likewise, I can put a product like Z2 on its knees after two washes.
What we like, we like. What we don't shouldn't matter. I find it hard to believe we have spent so much time arguing over the results of NXT.
Anyone who wants to make a product work, can get good results. People who don't want it to work will have bad results. I can do this with any product you give me.
When I first started writing the new Zaino product descriptions and usage for Sal, I tried my best to get bad results, and I did. There are all kinds of ways to screw it up.
When I tested NXT, I went into it with a positive attitude. I tried it on a dirty panel, I tried it on a perfectly prepared panel. I tried it with foam, terry cloth and a tee shirt. I even tried a second coat, and I put it on silver. I did not experience any of the negative problems others have described. I made it last by using a good shampoo and an excellent QD.
What I didn't do was pick NXT's MSDS apart, because, quite simply, it doesn't matter. All I wanted to know is does the product make my paint finish look good (yes), was it easy to apply (yes), was it a reasonable value (yes), and does it protect my paint between waxing (which for me is about every two months). Everything else is esoteric BS for people who need to get a life!
db
But what does that matter? 
or whatever. 