Sanding between coats of varnish or paint helps level the surface and removes settled dust and bugs. IS THERE ANY SCIENTIFIC OR MECHANICAL EVIDENCE THAT SANDING IMPROVES THE ADHERENCE BETWEEN COATS OF THE FINISH ITSELF? Finishing raw wood I usually put on two and sometimes three coats before doing any sanding. The reason for this is that it saves sanding time, and adds buildup for more effective sanding. I have never experienced a failure of adherence between multiple coats of finish even after years of use in varying conditions of exposure to moisture and sun. R.C.