I’m having trouble getting powder to stick to brazed joints (brass) on a 4130 steel tube thing I built (it’s similar to a steel bike frame). I blasted the heck out of the areas with aluminum oxide and it still happens in some places, not in others. Visually, it looks very clean (no flux). It seems to apply OK from the gun, but somewhere in the curing, it “disappears”.
Has anyone else had this happen and figured out what was wrong?