All I can tell you is that from personnal experience, a compound like M105 on a microfiber cutting disk on a long throw DA was not able to remove McKee's 37 Paint Coating. I upgraded to 3000 grit Meguiars Unigrit and that too was unable to take it off. When I sanded with 1500 it removed it completelly in 1 pass. People say it's easy to remove with a compound. I wonder how they know the coating is gone.
Well, how did *you* know that it wasn't gone after M105, but was after wet sanding?
After sanding with 3000 grit, the paint should be dull. I have done it often enough to know what it looks like while there were a few spots that were duller than the rest after 4 passes, water was still beading like crazy on it. So it dented it but did not remove it.
Water beads only means the surface is hydrophobic, which can be for many reasons. Doesn't mean it (still) has a particular coating on it. Freshly finished or polished paint is also usually very hydrophobic (even though it might depend on the actual material used). Contact angle would be more a giveaway, because to reach the 100-110 degrees of a typical ceramic coating, you need the surface to have specific micro-structures, which you can't achieve by just polishing it.
Sure if you spend a lot of time with 3K paper or compound, I am sure eventually it will come off.
No, it should be really just a single pass in most cases, even with a compound. And given enough pressure and of course water (which will carry away the already abraded particles), even a 3K sandpaper can not only remove a few microns (which is needed to definitely remove any and all ceramic coatings), but actually burn through all the clear coat in less than a minute, even if used just by hand, let alone with a machine.
All I can say is that 3000 did not work for me.
Well, I'm not saying that it did or didn't work for you, because I obviously can't know, and you might be even right in that particular instance. Meaning it's very well possible that for whatever reason you couldn't remove a coating in X time with a particular compound - but really, that could have many reasons, which we can't verify either (like your pad being saturated, not using enough pressure, the compound having been deteriorated, etc). Anyway, generally speaking, wet sanding should be an overkill for removing a ceramic coating.
The point I was trying to make by asking the question was: How do you know that compound is enough to remove it.
The most sureproof method would be checking the paint thickness. If it has decreased several microns, then obviously nothing of the coating could have been possibly left on the surface, because it's only 0.5-3 microns thick (and even that are manufacturer claims, which I wouldn't take for granted).
So if you tried to remove Cquarz with a compound and it worked great, maybe it's not the best product out there. McKee's is half the price and looks like it offers a heck of a lot more protection. When it comes to professional coatings, there should be no way you can remove them with a compound. Gtechniqs is very clear on the fact their pro coating will have to be sanded off if you apply it incorrectly. So I am assuming any pro coating would have similar restrictions.
As already explained above, generally there's no difference in this regard between using a sandpaper and using a cutting compound, because the only thing they definitely differ in are the carrier medium: paper in the case of the sandpaper, and oil, water or other solvents in the case of compounds/polishes. Of course there can be also differences in grit size (compounds and polishes tend to be at higher end of the scale, while sandpapers obviously on the lower), which in turn also affects the speed they're cutting at; and there can be also differences in hardness of the actual abrasive particles, which determines what kind of material they can cut down (ie. only materials that are less hard).
But regardless of this, it's generally pointless to say that some coating can't be compounded off, but will need to be wet sanded, because "compound" and "sandpaper" only denote the carrier medium, which is not determining in whether that particular abrasive can cut down something or can't, and not denoting the cut speed either - which again, is correlated generally with grit size, and how and whether the abrasives are diminishing, but not whether they're glued onto a paper or submerged in a solvent.
So, if a coating can be removed by a sandpaper of a particular hardness, then it can be also removed by a compound that's using abrasive particles with same or higher hardness. And the speed at which the material will be removed is also only dependent on the grit size and the diminishing properties of the particles, not the carrier substrate.
The general rule of thumb should be here - as always - to use the least aggressive method that brings you the desired results in a desired time frame. However, considering that the coating's thickness is a few microns max, a cutting compound should be more than enough in "aggressivity" to remove the stuff in a timely fashion.
