Hot take: I thought flux was mostly for show until a rail job in Cheyenne last month
I figured a clean wire brush was enough for most welds and never messed with flux on mild steel. Then my forge scale kept creeping into a 3 foot rail project and an old smith told me to dip the joint in borax before the heat, and the seams came out smooth on the first pass. What got you to change your mind on flux, or do you still skip it?
That rail job sounds like a real pain, and I get why you were pulling your hair out. I had the same thing happen on a gate I built last spring, scale flaking off into the weld and leaving these ugly little pits no matter how hard I brushed. My old wire brush trick worked fine on small stuff, but once the steel got good and hot, that scale just laughed at me. A guy at the co-op told me to try borax and it cleaned up the seams like night and day. Feels good when a simple fix saves a whole project.