Painting over mill scale??

admin

Looking for some opinions from guys who have long term experience with the results of painting over mill scale.  Obviously anything loose has to go for a good job,  but what about scale that a 40 grit flap wheel just polishes shiny, unless you lean on the grinder, or use the edge of the wheel? I have gotten different answers from my buddies who paint, so I thought I'd pick the brains of the vast welding web knowledge base.My question is more about the functionality of the job over time and less about the aesthetic quality.I'm also curious if any particular type of primer would make a difference.
Reply:I've worked with rect/sq tube some.  Ran thinner over it then hit it with a 80grit flap wheel, then thinner again prior to painting. Used two stage epoxy and that is expensive as you probably know, but holds good.Ran into what you are referring to with channel and angle.  Used same appraoch as above.  I am sure we did not remove the hard core scale, but the primer/paint is holding so far.  I am sure someone will chime in with the cure you are seeking.GeezerPower Mig 255C185 TIGBlue 175 MIGRanger 8 Kohler 20HP1974 5K Lincoln/Wisconsin Powered (Cherry)Victor/Harris O/AK 487 Spool Gun
Reply:Thanks for the reply geezer.Anyone else? I know we have some paint guru's here somewhere!
Reply:Time will tell, I guess. I've been using Flood Penetrol as a primer on my metal projects. It bonds good and makes a smooth surface for the paint. I built a cart for my chopsaw a few months ago and last week decided to give it the chip test. I hit one leg of the cart w/ the point of my chipping hammer. It dented the metal but the paint held firm. I guess I'll find out in the future if it's a good primer.                                 MikeOl' Stonebreaker  "Experience is the name everyone gives to their mistakes"Hobart G-213 portableMiller 175 migMiller thunderbolt ac/dc stick Victor O/A setupMakita chop saw
Reply:I used a couple of hundred feet of steel tubing for a recent project.  I cleaned the oil off with mineral spirits and let it dry.  After that, I went with Ospho conversion treatment and let it dry for a day.  Followed that with iron oxide primer, then paint.  It's been a year since I did it and no problems whatsoever.America Needs AMERICA'S Oil!!!"Global warming is the greatest scam in history ...There is no run away climate change. The impact of humans on climate is not catastrophic. Our planet is not in peril."--John Coleman, Founder of The Weather Channel
Reply:I think you want to paint over the mill scale for most applications.  Clean it first, but if it doesn't come off with a flap wheel, then it's probably going to stay in place longer than the paint you put on it.Jack OlsenMy garage website
Reply:Mike and Steve, thanks for the input.
Reply:Originally Posted by Jack OlsenI think you want to paint over the mill scale for most applications.  Clean it first, but if it doesn't come off with a flap wheel, then it's probably going to stay in place longer than the paint you put on it.
Reply:If you just have loose paint on the expanded metal, when weather permits a good pressure washer will remove any loose paint if you go over everything w/ the tip a couple of inches away. By the way, the penetrol is thin enough to run in a spray gun. It orange peels a little but smooths out after a few minutes. The only drawback is it takes a min of 24 hrs to dry. There's very little smell/fumes so it can dry indoors.                              HTH,                                     MikeOl' Stonebreaker  "Experience is the name everyone gives to their mistakes"Hobart G-213 portableMiller 175 migMiller thunderbolt ac/dc stick Victor O/A setupMakita chop saw
Reply:If the pieces are structural then follow Steves advice. Iron Oxide primer is good stuff. If you are using it in an automotive capacity such as a truck bed or box that will see repeated dings I would look to some other primer/paint combination. Either way unless it's already loose the scale isn't going anywhere.
Reply:I used to do a lot of structural steel work for local construction companies, and I would clean the oil off with degreaser and a rag, and the loose mill scale I would hit with a wire brush on a grinder. It wasn't perfect, but it was how we normally did it. Most of the time we used Rustoleum red primer.
Reply:stack 4-5 zirconia or resin fiber sanding disks together 5/8 or 7/8 arbor hole whichever your grinder is.......you wont need a backing plate this way and the flex makes them contour to the surface and strip off old paint or rust like Mad..!  Use Makita or DeWalt 36,40 or 50 Grit........they will fix your problem in literally seconds........If the scale was bad and left pits . Prime with a heavy fill Polyester Primer like Evercoat Feather Fill G2It'll go thick enough on in 2 coats to fill  anything......then dry sands flat like butter.        thermal arc 252i  -  millermatic 350P -   miller XMT, cp300ts, 30a 22a feeders, buttload of other millers, handfull of lincolns, couple of esabs  -   Hypertherm 1250 G3