I am lucky that I have a very clever man who is called 'nick the blaster' he always cleans and prepares my frames with an inteligent appropriate blast he is good I have seen him clean car bodys that look like rust lace work.
You need to have clean metal , warm and dry before thin powder coating, luckily Nick the blaster is near Pete the powder and in case you are wondering my 27 Scott frame and my 26 Douglas frame tubes still show proudly through the paint the slight rust pits that they gained over their ninety odd years of use and missuse -because thats how I like them to look. Nothing looks worse than excess makeup on an old woman.