Eli5: Why both primer and paint?

Question

Eli5: Why both primer and paint?

In: 6

Answer 1

Say you making a sandwich but you want ingredients to stick, you’ll use say margarine/butter on bread right? Won’t be perfect but it will stay.

Now make sandwich without margarine/butter ingredients will likely fall off as you try and eat.

Same applies to primer and paint, say you paint a car bumper raw just paint eventually it will flake, but if you put on primer it will stick to bumper that will allow paint to stick to primer.