Flour and water on a car's paint job won't ruin the finish, but removing the mixture is a nasty hassle. Pranksters will empty bags of flour onto cars as a joke; and unsuspecting owners will do what comes naturally: attempt to wash it off. Flour, when it's mixed with water becomes paste. Attempting to wash flour off your vehicle's paint will turns the flour into a glue-like mixture, making it a bit harder to remove.
Park the car in a shaded area -- the further drying of the flour paste will hinder the removal process.
Soak some towels in hot water. Do not wring them out. Lay the wet towels on top of the dried flour mixture. Dried paste has the consistency of brittle cement. If you attempt to scrap the paste, it will scratch the car's clear coat.
Spray the towels liberally with water, every 20 minutes. Your goal is to to hydrate the flour paste so that it can be washed away.
Lift one towel at a time and scrub the area underneath with a sponge. Rinse the towels in a clean bucket of water and reapply them if the flour paste is too dry to wash off easily. Sprinkle powdered washing powder over the surface of the car and wash it with a sponge. The washing powder contains enzymes that break up food particles, giving extra scrubbing power without scratching the paint job.
Repeat this process until the flour mixture is removed. Wash the car with soap and water. Buff it dry with a microfiber cloth and apply a quality wax.
Chipping away the dried flour mixture will damage your car's paint job. Washing flour off a car's paint job is labour-intensive.