What is primer for?

If you were recycling an old ornamental gate to be installed at the entranceway to your front yard, you would first scrape and sand all the original paint off of the metal. After the surface is cleaned and prepared for new paint, you would first paint with a " primer " coating.

This initial coating is specifically engineered to give maximum adhesion to the bare metal surface and to rustproof it.

Then the next layer of paint would be your final choice of colour and type of paint, oil-based or rubber etc.

Often, you see an older car with some reddish brown spots painted on some places. It certainly looks ugly, but it's only temporary. This is the primer coating applied to some damaged areas of the car body after the dents, holes, etc. have been repaired. After the primer has thoroughly dried, the owner would then cover those ugly spots with a second layer of paint matching the rest of the car.