For good adhesion you really need a clean surface with nice deep scars and surface irregularities. For this I used my Fein Multi-Master and the Carbide Triangular Rasp attachment. This is a hard, alloy tipped sanding attachment. It produces about 5 times the sanding performance of 40-grit paper, but won't load up with residue. It also LASTS for a long time because it is carbide.


If you don't have a Fein, or other multi-tool, don't worry as about any wire wheel brush on a drill will do a similar job or 36 grit discs on an angle grinder..