My car has Supagard, can I put a ceramic over it?

This is not something we would recommend, Supagard is a polymer sealant* which is permanent. It is strong and lasts years. It is really good stuff, and will do a great job of protecting your car.

However, it is not as strong as ceramic, and so would you want to put a tougher coating on a softer coating? Would that be like building a house of sand? Really, we don't know. After all, the paintwork is softer than ceramic and by putting a ceramic coating on it, you are toughening it up.  So doing this might work fine, or it might not. We aren't going to pretend to know.

Our guess is that it would be fine. But if it did go wrong, that would be a very expensive experiment as you have paid for a polymer coating, a ceramic coating, to ruin your car. However, what we can do is remove the polymer coating, so this is how we would tackle the issue. We can replace the coating with ceramic, but we wouldn't attempt to put it over the top. 

*Supagard seems to have a new formula called Bionic - It doesn't say what this is, but we assume it's still polymer based, as they haven't said it is silica or carbon.