If, for reasons, i gotta do a long term paint foray, i do, use the reducer after scuffing, etc... In all seriousness, any foreign substance right down to smoke from cigarettes ( yeah, im caught), will take to the surface and mess the base.... Clean is the most major deal, IMO, and I have a drop down booth in my shop ceiling with a shroud and exhaust fan to get the floating particles and overspray out.... there are tricks from wetting the floor?... to whatever... ( ideas welcome).... KK is so easy, from mixing to whatever, a mike larson can do it...... even with a 17 dollar gun from HF..... Its great paint, nitro proof, and flows/covers well...... IDK, advancing from the rattle can outside, ( little gnat trails, lol, dust, and whatnot).... tellin ya.... follow the directions and you cant mess it up!.... Mike