This allows the paint to «do it's thing» — basically scientifically — to let the molecules settle, connect and really adhere to the surface. (thepurplepaintedlady.com)
Because you want the dough to adhere to the surface without sticking to it and pulling apart. (soupaddict.com)
The primer at that time wasn't up to the task of keeping paint adhered to the surface of the vehicle and so, after a few years of baking in the sun, it lets loose and vehicles start looking like yours. (mechanics.stackexchange.com)