I thought this was nicely explained.
From
Meguiar's Australia eMag
Issue 4, Autumn 2006
"We regularly receive calls and emails from people that have been told by their panel beater not to use polish or wax that contains silicone. These comments from so-called "experts" are driving us demented, so lets bust the myth and settle this once and for all.
Thankfully, this poor advice is only coming from a relatively small percentage of panel shops but lets clarify the facts. Car painters don't like silicone for the following reasons:
(a) If a product containing silicone is used
inside a panel shop there is a possibility that some of the silicone will end up floating around the shop in the air, and work it's way into the spray booth. This will cause paint adhesion problems (often referred to as "fish-eyes") and the contamination is difficult to remove from the paint shop. The more a product is aerated the more likely the chance of a problem. Polishes/waxes containing silicone (or any other non-paintable substance) don't usually aerate, but they can contaminate a paint shop by getting on the painters clothes and hands.
(b) If a silicone based polish or wax is applied to uncured (fresh) paint, it will seal the finish before the paint has had time to fully cure. This is likely to cause "solvent entrapment" which leads to loss of gloss & poor resistance to watermarks & etchings from industrial fallout etc. Any sealant or paint protection product can cause this problem, whether or not it contains silicone.
(c) If any part of a car requires repainting, and silicone or any similar substance has
impregnated itself in the pores of the existing paintwork, the painter can also have adhesion problems. The products most likely to have this effect are the ones that overdose on silicone, or chemically bond to the paint finish. Both types of products have no consideration or understanding of refinishing or are not designed for use on paintwork. For example, if you regularly use a high silicone protectant on your external trim and usually get it on your paintwork, you are likely to cause adhesion problems if the effected areas need repainting. Or, if you have had one of the many "never polish your car again" paint protection treatments offered by car dealerships and some panel repairers, you may also give your car painter plenty of heartache when it comes to repainting.
The important thing to understand is that as long as the silicone content of any paint care product isn’t ridiculous, it can be quickly and effectively removed using a professional wax and grease remover. In addition, silicone is not the only ingredient that can cause repainting problems. Any product that is designed to seal or protect a paint finish relies on things not adhering to it, and therefore must be removed prior to painting.
So the real issue, from a car owners perspective, is "remove-ability" of car care products.To set the record straight
all Meguiars polishes and waxes are designed to be completely removed using a regular wax and grease remover. So too, are many other reputable polishes and waxes. Our advise is to be wary of particularly low priced brands (they don't cost much for a reason) or products that promise things that seem too good to be true.
Finally, a note on cured and uncured (fresh) paint. A new car's paint finish is "high baked" so it's fully cured when it leaves the factory (unless it's had some rework). Refinished paintwork (done by a Body Shop) is "low baked" when it’s two pack paint and air dried when it’s acrylic lacquer. Two-pack needs 7-14 days to fully cure and acrylic laquer needs up to 60 days, so we would always recommend that you wait the appropriate time before applying a polish or wax.
MYTH BUSTED !"
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