ive found another prep tool that works good is a propane torch,,,use it to heat a little bit,,,and watch the ooze come outof the metal pores,like a zit,,then use a prep juice,like brakecleen,paint prep or somethin,,,,,works good on absorbant cast iron,,,,,i do this before sanding etc sometimes,on a realdirty greasy part,,seemsto help adhesion,,,,,i learned this the hard way,,icleaned and painted a set of gtiwheels,,,,well as i was baking them in the oven,around 200for an hour,,icame back tosee these lilbubbles,and when i squeezed them,,oily crapcame out,,,,,needless to say it was a mess,,had tostrip and redo themetc,,,,,,,hey try this,,,take an old con.rod,,get it verry clean,,then put it in a bucket,put an inch or2 of oil in bottom of bucket,,,come back a 2-3 days,,look top of rod is "wet",,cool eh????capillary action at work,,,,,