I paid $65 for a "rust converter" kit that promised no sanding, and it peeled off in 6 weeks
I bought this kit at a swap meet in Dallas back in March from a guy who swore it would turn rust into a paintable primer. I brushed it on the rear wheel arch of my son's Silverado, let it cure two days, and shot color over it. Six weeks later the whole patch lifted in sheets and there was wet rust underneath, so I had to strip it back to bare metal and do it right with a DA and epoxy. If you see a jug that says no sanding needed, just walk away. What is your go to method for wheel arch rust that actually holds up?
I used to be in the rust converter camp too, thought I was being smart skipping the sanding on my old Tacoma's arches. Did the same thing you did, brushed it on, waited, sprayed Duplicolor over it, and it looked great for about two months before it started bubbling. The thing nobody tells you is that phosphoric acid only converts the top layer, and if there's any pitting underneath it just keeps eating. Pulled it all off with a knotted wire wheel on an angle grinder, hit it with epoxy primer, and that patch is still solid four years later.