I polished my desire red cupra and then applied Sonax CC36 ceramic coating by friend who is a certified Sonax detailer.
It is not optional whether you apply ceramic coating inside or outside. Applying it outside is simply said impossible without trapping dust and debris inside the coating or between the coating and clear coat. It will probably last a couple of months and then come off, worse scenario is dust gradually releasing and scratching your paint and peeling the coating. Yeah, its that bad.
Before applying the coating the car should be polished to remove previous coating and take out swirl marks and minor scratches. After that the car should be degreased with professional-grade degreaser, and then the product coating manufacturer recommends before coating the car. The garage should be perfectly clean while working, preferably floor washed with water to prevent you agitating the dust while walking around. My guy locks himself inside while working so nobody would open the door and let the dust in. Then you apply a couple of layers depending on the product and let it dry for at least 12 hours in the same area - dust free.
You coated the car and left it exposed to elements immediately. When I detail my car (using high quality products) the layer of dust is visible within 5 minutes after drying on roof and glass. Also because my car is red I have at least 10 mosquitoes and other insects on the car trying to bite it.
Ceramic coatings last between a year and 3 years depending on climate and care you give it. I always used 50-50 dilluted sonax brilliant shine detailer as a drying aid. It (hopefully) makes a protective polymer layer over my coating and impoves gloss even further. I can tell whether its still on the car because when I apply it the paint becomes grippy to touch, its not slick anymore. It stays on the car for maybe a week or 2, depending on weather. When its off the car is slick again. Hydrophobic properties are crazy, but when you get traffic film on the bottom areas its not hydrophobic anymore so I know its time to wash. Ceramic coatings are not a perfect solution for everything, but they do work by keeping your car cleaner and making it easier to wash.
I also coated my alloys with Gyeon Rim but the cupra brake dust is so harsh that it still stays on the alloys, but its a bit easier to wash and keep the soft acrylic back paint on the alloys scratch free.
I can't stress enough that you should not expect the coating to protect from mechanical impacts. It is 8um thick after all. I hit the paint accidentally with my macbooks magsafe adapter and damaged the clear coat yesterday. Rocks are making a mess of my front bumper. I have 2 spots on my alloys with rock chips. You can't save your car from impact damage, what the coating does well is save it from washing and drying damage, UV radiation, acid rain, snow and cold.
BTW it is impossible to have active foam on your car when its coated (it just settles to liquid immediatelly, it wont foam) or apply a vinyl
sticker, it just comes off. If you can, the car is not properly coated.
Here are some images of my cupra:
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