When surfaces need rust protection, people spray anti-corrosion paint. They choose specific thicknesses for both the primer and topcoat. Sometimes an extra middle layer is added.
Why do we use different primer and topcoat? Can't we use the same paint for both? Let's find out!
Primer touches the material first. Its main job is to stick well-without this, the paint peels off quickly. It also fights rust by blocking moisture and chemicals. Plus, it fills tiny holes to keep contaminants out.
Topcoat faces the outside world. It needs to last long and look good. It protects against sun, chemicals, and heat. The coating must also be tough enough to handle scratches and impacts. Lastly, it adds color and shine for a polished finish.
In short, primer and topcoat do different jobs. They're made differently and can't be swapped. (文章来源： iMechanics机械)
