I asked Mike Phillips in another thread about the concept of layering. His posts are so informative that I thought I'd post his reply here for your enjoyment:
"Hi Suginami,
What I am going to write here, is what "I do", that is, my opinion.
It is not what Meguiar's recommends. So what they say is the official word.
What I like to do after machine cleaning and machine polishing a finish is apply a coat of #20 Polymer Sealant.
It turns the surface very slick and as far as a wax goes, it lasts a long time.
When my customer is paying me $300.00 plus to polish the paint on their car, not including chemical costs, they want the finish to,
A. Look Good
B. Last a Long time
#20 makes the surface slick, "I believe", (that's my opinion), this helps to reduce towel scratches. (It makes it pretty darn slick), it also dries very fast, is incredibly easy to wipe off and it last for a long time, months, depending on the environment, how frequent it is washed and whether a premium wash is used or a detergent, #20 can last up to 6 months
So I always put that on first, it seals the pores, without question, and turns the surace very slick.
Next I like to apply a coat of #16 for personal reasons. It is too hard for most people to remove without getting frustrated, or potentially scratching their paint. #16 is Meguiar's first wax, it came out in 1950 it has been improved over the years as science advances. It is a heavy wax or a high molocular weight wax. It is a blended wax, it gets it's protective characteristics from a variety of ingredients, not just carnauba.
And while some web wax enthusiest drone on about how carnauba "melts' off your car when exposed to the sun, I would have to disagree. That's a blanket statement and while it may be true of some products it is not true of all products.
Meguair's not only makes automotive waxes, they also make Fiberglass Mold Release waxes, some of them are good up to 600 degrees, F.
On the back of the can of the #16 Professional Paste wax it says, "Formulated for durable protection in the hottest weather".
For what I do, I like it. The only way you can know if you like it is to use it. I recommend you try the Medallion first. It leaves a very dark finish. On my test panel it was darker than Zaino even after multple "thin" coats. On both clearcoated black and black lacquer.
Interesting thing. The waxtest.org listed Medallion as a "Carnauba" wax, when it is a synthetic and the #16 Professional Paste wax as a "Cleaner/wax", when it is a "Pure Wax".
#16 is only for use on perfect finishes, like the kind I produce after machine cleaning and machine polishing using a rotary buffer and the Meguiar's cleaners and polishes and their foam buffing pads that they have offered since the Beach Boys' came out with, "Help me Rhonda", since the Rolling Stones, came out with, "I can't get no satisfaction", since Gilligan's Island came on t.v. (I think it's funny that Meguiar's invented foam pad polishing, since 1965 and it has only been since the mid-90's that anyone else even had a foam pad on the market, but now those that do proclaim themselves to be experts and don't ever mention the fact they got the idea from..... Meguiar's.
Typically, you can apply a synthetic wax over a synthetic wax for a layering effect. That is why Meguiar's has always said, two thin coats is better than one thick coat. Thick coats are just plain hard to remove, plus it wastes a lot of wax, whether it's Meguiar's wax or anyone elses.
You can apply a coat of a Meguiars' Pure Wax, like the #16 over a Synthetic.
You can apply a pure wax over another pure wax.
You cannot apply a synthetic wax over a Pure Wax like the #16, it appears to liquify it to the point of removing it.
I know this is true in the mold release industry also.
As far as applying a coat of the #7 Show Car Glaze, over wax, be it a synthetic or a natural ingredient base, Here is the deal.
1. If your intention is to "polish" the paint, you should polish then wax over the polish. This acts to "lock" or "seal" the polish "in". Polishing first is the correct procedure.
2. If your intention is to make your paint look "wet", then you "can" apply, or in my case, re-apply an application of polish, on top of the wax. This would include, #7 Show Car Glaze, #81 Hand Polish, Deep Crystal Polish, #5 New Car Glaze, #3 Machine Glaze, and even the #80 Speed Glaze, (its quite oily).
The idea is to make the paint look wet, and oil products can do this. #7 Show Car Glaze is one of the most popular "true/pure polishes" ever sold. It has an enormous following. There must be a reason. There are no abrasives whatsoever in the #7 Show Car Glaze for those of you who always refer to "Polish" as an abrasive product.
Because Meguar's polishes are water solouble, (the are not waxes, see my upcoming book for a discussion on "Words" and their meanings"), the effect is short lived. That is to say, once you wash the car or it is exposed to inclement weather, the polish sitting on top of the wax will will dissappear.
Now show cars' are not typically washed a lot or driven in inclement weather.
Used correctly, Meguair's #7 Show Care Glaze works great.
Now, some of the oils in the polish will penetrate past the wax and into the paint, that is because you can never completely "seal" a surface with something you pour our of a bottle or scoop out of a can. (You can't do it from the factory with fresh paint either, at least not "completely", paint has pores, you can argue about how porous some paints are, but in the end... they are all porous to some degree and with time, even the tightest pore paints become more permeable)
So yes, in my opinion the benefit to applying a coating of #7 over the wax is for short term gloss, hiding fine scratches, depth of color and making the paint look wet.
Case in point.
I buffed out a 1956 Nomad for a guy who tried to wet-sand, cut and buff it himself. He ruined it. In fact, he had not taken it out of the garage for over a year because of the way it looked. He had it painted, "Viper Red". (Nomads are "BIG" in case you never noticed and messed up finishes this big cannot be "quickly" fixed).
I spent three days on his car. The last day I worked on it, although it had a flawless finish, I applied a thin coat of #7 Show Car Glaze. That day, I repeat... that day he was taking it to a "Show 'N Shine". It was the middle of August, bright sunny day.
It had to look flawless. He was so excited to show it off. I used the #7 to make his paint look it's best, to look wet.
He gave me a $100.00 tip
He loves his "New" car.
If you have further questions, send them to my home e-mail
PolishPro@Mindspring.com
I hope I was able to answer some of your questions on polishes and waxes.
Mike Phillips"