I've 1 rear wheel arch lip - abraded... o Drop car at tyre shop, wrong width tyre fitted o Collect car, pick up gravel, every corner noise of paint abrasion o They fixed it with what seemed to be primer & top-coat
Several years later... o Wheel arch lip paint & primer cracked, flaking off o No scaling, no in-seam scale, no in-seam expansion o Metal is sound, no recessed lands from corrosion o BUT numerous surface-rust pitting :-)
Also... o Small black rust patch had moved up onto the body o Wire brushing gently brings it back to shiny metal o Some small black rust dots (2-3mm) remain o Wire brushing them individually brings shiny metal o Surface is then faintly rough, but shiny & solid
Basically as a result of no paint on the lip there.
Option-1 -- Galvafroid + Galv-Metal-Primer + Topcoat
Q: Do I have to wire brush all pitting & black rust dots?
---- to get all perfectly shiny would take several hours
---- 9.6V Makita & 10mm brush does beat than emery cloth
Q: Is there a micro-brush I can use to get in those pits?
---- engraving tool, but would that just eat such thin metal
Q: Can automotive steel withstand wire brushing ok?
---- I guess so & rust erodes faster than steel
---- steel is non-scaled, but obviously of finite thickness
Option-2 -- POR-15 + Topcoat
Q: Most paint-over-rust things do not work well?
---- Ku-Rust & Hammerite aren't "good but toxic" anymore
---- POR-15 is *supposedly* better, but what rust limit?
Is it just a matter of wire-brush, wire-brush, wire-brush? o Numerous tiny specks - pitting & black flecks o Not using much force on the 9.6V drill/brush - just using speed
Could do with a wire-brush inset via a bearing into a handle. That way it doesn't zing across the (as yet) undamaged paint :-)
Objective - wheel arch lip & that body bit ok for 18 months. o Car has light use -- 2x 15 mile trips once a week o Wheel arch clean -- no debris, cleaned after every snow
Googled lots on POR-15 & Galvafroid.
POR-15 comments seem to lack saying the risks o I suspect it prevents future welding if ever the need? o Real rust will obviously continue to perforation?
---- chemicals only penetrate a tiny distance
---- or is rust-pitting & black-rust tinging shallow enough?
Galvafroid is electrochemical, cold zinc galvanising o I'm sure this must require really new shiny steel o Even faint black smudges are not steel so not a zinc base?
I'm avoiding just hammeriting the lip, I don't trust that stuff. Rust is never beaten, but slowing at this stage should be possible.
Anything else to consider?