For adhesion to take place, the coating and substrate must not be separated from one another by more than approximately 5 A - about three times the diameter of an oxygen atom. Any contaminant on the steel will increase the separation and decrease paint film adhesion. Moreover, reactive sites on steel at which adhesion can occur are masked not only by contamin-ation, but also by chemically bound species which may themselves satisfy sites on the steel that would otherwise be available for reaction with the paint vehicle. Thorough surface preparation removes such contamination, and exposes many more reactive sites, thereby dramatically increasing the amount of surface area where adhesion can occur. 可以看到表面处理的目的就是清理待施工表面，使表面清洁，从而增加表面能，再就是通过打磨或者冲砂，来产生粗糙度，粗糙度的好处是增加表面与涂料之间的物理性螯合，还有一点就是增加表面的比表面积，从而增强结合力。至于粗糙度，也不完全需要用冲砂的方式来实现，像现在流行的bristle blaster,同样可以达到70um以上的粗糙度，等同于冲砂的效果。
