Painting over mill scale

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Has anyone painted over mill scale?  Did it hold up, or am I better off taking it down to bare metal?  Thanks in advance
Reply:I would remove the loose stuff. For the most part a quick brush with a wire wheel is all I do. Not worth the effort in my opinion.
Reply:Wipe it down with acetone.I've gotten TONS of oil off new hot rolled square tubing.Just a couple welders, big hammers, grinders, and torches.Work will free you.Men in dirty jeans built this country, while men in clean suits have destroyed it. Trump/Carson 2016-2024
Reply:If u want it to last take it off as much as you can
Reply:We usually prime and paint right over the mill scale. Here lately our carbon pipe has all been getting sandblasted before we weld. (Which is great) but that too just gets primed and painted when welded out.
Reply:All depends on the the finish you are after. Gates and things like that, take off the loose stuff. Fine finishes, sandblast. You can always use a 2k type fill primer and sand down to get rid of the lines from where some was removed if you want a better finish but dont want to grind it all off.
Reply:we have shipped millions of pounds of red iron with full blown mill scale that has just been shot over with water born red oxide primer with zero problems.   but most of the time it just sits inside water proof walls.  so your millage may vary.Vantage 500's LN-25's, VI-400's, cobramatics, Miller migs, synch 350 LX, Powcon inverters, XMT's, 250 Ton Acurrpress 12' brake, 1/4" 10' Atlantic shear,Koikie plasma table W/ esab plasmas. marvel & hyd-mech saws, pirrana & metal muncher punches.
Reply:Any amount of heating and cooling or mechanical stress will cause the mill scale to pop off along with any paint you put on top.  If your structure is not subject to any kind of environmental or physical stress go ahead and paint on the scale, otherwise remove it.  Needle scalers work well.
Reply:One of the issues is the profile ( ridges & valleys) of the steel.  Primers have a higher solids content which fill the valleys and cover the peaks.  Your top coat then has a nice even substrate in which to adhear.
Reply:I generally find that paint on mill scaled pipe holds up ok but paint on mill scaled plate does not.
Reply:Thanks everyone for your replies.  Much appreciated!!
Reply:Ive painted and seen painted lots of steel over the years with no mill scale removed, or anything removed for that matter... With that said, ive seen lots of steel that is rusty get painted so it doesn't get more rusty... That's how the marine world is at least..
Reply:Anyone tried these yet?
Reply:that flex cut seems cool but to os pricey?  Has anyone tried it?
Reply:I've always felt mill scale that is well adhered to steel after normal cleaning and brushing is fine to paint over. I am very picky about my paint jobs, but I can't remember failures due to mill scale.
Reply:I wire brush by hand, then paint.  Have not had any issues.-AaronJet 17.5" Drill Press1942 South Bend 16x84 Lathe1980s Miller 320A / BP --- 2013 Power Mig 2562012 Jet 7x12 Horizontal BandsawVictor O/A Setup
Reply:Thank-you everyone for your responses.  I still am removing mill scale and painting but I am experimenting with leaving mill scale and painting over it to see how it holds up.
Reply:I usually hit it with a wire brush on a drill or grinder, spray rattle can auto primer on it, then paint it.  What doesn't come off with the wire brush is probably not coming off later.