Prepping mill steel for paint

[slackdaddy1]

I have some typical "welded rectangle/square tube steel" I fabricated some jeep parts from.
This has the typ mill oils on it, what is the best way to prep this metal for paint? I have wiped it with mineral spirits multiple times, and it is still slightly oily.

Thanks,
Slack

 

[kazlx]

Zep degreaser works really well. Really depends on how big the pieces are and what you can/can’t get to.

My favorite way is to just take it to a sandblaster

 

[Firebrick43]

Sandblasting is best. For things I can't I wash with purple power and then coat with Ospho. Even if the metal is not rusty it makes paint adhear so much better it's worth the effort.

 

[LXCam]

I use acetone and after I no longer get any oil residue hit all of it with a torch. That burns off the last of any residue plus any fur balls that might have clung on. Everything we rattle can around here turns out really nice using that method.

 

[RCL]

I get good results with the acetone.

 

[PCustoms]

Acetone or simple green, depending on what I am doing.

Longest lasting paint on my fabbed truck parts is th tubing that I used phosphate acid (would have to go look at what the label says, HD sells it) and then rattled with rustoleum pro black.

 

[lakeroadster]

I agree with sandblasting first. It gives the surface "tooth" for the primer / paint to adhere to.

 

[Jason280]

I get good results with the acetone.

This is what I use as well.

 

[porschedude996TT]

Lacquer Thinner for aluminum, steel with no surface Mill Scale, if there mill scale, I glass bead. My last resort for removing adhesive and heavy oil on any metal is MEK. The MEK fumes/smell makes me feel the stuff is going straight to my kidneys and liver and damage is impending.

 

[slackdaddy1]

Thanks for the heads up,
I'll wipe some more, then hit it with Phosphoric acid.
What would be a good brush on primer/top coat (satin black) for these under carriage pieces of a jeep?
Or rattle can?

Slack

 

[Git]

POR15 and if it would be exposed to uv light, use a topcoat

https://www.por15.com/

 

[sanddan]

I use "Wax and Grease Remover" to prep surfaces for paint. I use a Sure Shot to spray it but it's not necessary.

https://www.amazon.com/dp/B008QDSVPE/?tag=atomicindus08-20

 

[Elsinore13]

Do you have a PPG automotive paint store nearby? Their DX579 Metalprep followed by DX520 Galva prep cleans the metal and etches it for adhesion. For a great primer over raw steel such as that, their DP line of epoxy primers are some of the best out there. DP40 is a greenish gray, DP 50 is gray, DP90 is black. Apply it and you can topcoat within 7 days or so before having to sand it. Although I no longer use PPG products I still keep those products on the shelf at all times.

 

[A**holes Garage]

denatured alcohol

 

[Brian_WK]

Small stuff Simple Green, Big stuff Trisodium Phosphate, Really nasty stuff Muriatic acid Be Careful with this stuff and use in a open area as the fumes will rust other things in a confined space.

Brian

 

[zmotorsports]

When working on new metal I initially use Acetone to remove the oil residue prior to metalworking, machining and/or welding. After the components are completed if I'm going to paint them I wipe with PPG's Wax & Grease remover (DX330) then run over them with a DA sander to prep and give the new surface a tooth to bite into. Prior to paint I will use either a metal etching primer if I am going directly to paint or PPG's DP epoxy primer if I am going to be using a primer surface prior to paint.

If the part(s) will be powder coated, I still use the Acetone prior to machining/welding/fabricating but once the component is complete, I drop off at the powder coater and they sandblast prior to commencing the coating process.

 

[kkroger]

Rag and acetone or brake cleaner and a rag...

 

[pgk]

Sandblasting is best. For things I can't I wash with purple power and then coat with Ospho. Even if the metal is not rusty it makes paint adhear so much better it's worth the effort.

+1 on this combo Mil scale is a total pain..

 

[Jack Olsen]

Just or future readers of the thread: mill scale and the oil used to stave off rust are two different things. I think the easiest way to deal with the oil is a degreaser cleaner (even Fantastic or Formula 409) and then a final wipe with acetone before you paint.

Removing mill scale before paint is something I believe life is too short for. But sandblasting or sanding will do it. It depends on the project, of course.

 

[kkroger]

By far the easiest way to remove Mill Scale on Hot Rolled is to use Muratic acid, in a spray bottle next to your A Hole Neighbor's favorite car, Just keep the surface wet until the scale floats off then hose it off with fresh water... repeat as necessary... or just get the scale free cold rolled cousin....

 

[pgk]

Muriatic acid does works great, just don't use it inside your garage, the fumes tend to rust any metal they come in contact with.. I would think after rinsing a little baking soda to neutralize the acid to help with flash rusting..

 

[kkroger]

Baking soda won't do anything except neutralize the acid won't do anything for flash rust, will just make another mess you need to clean off the metal to paint, Rinse with clear water dilute dilute dilute, then dry as fast as possible, but yes don't do it indoors.. the Fumes ALONE will ****... 8000 square foot shop if acid gets used in the shop the ENTIRE SHOP everything steel ends up rusted... EVERYTHING!

 

[pgk]

Didn't realize using baking soda wasn't necessary, I just checked a website steel patinas they said the same thing, learn something new everyday! They use Hydrofluoric "Muriatic" acid and water 1 to 1 ratio. 18 years we put down a epoxy coating on our garage floor, first cleaned with soap then Muriatic acid and rinsed. We had laid down small mound of baking soda the width of the garage to keep the acid from staining the driveway and or killing the grass, seemed to do the job.

 

[kkroger]

I just use straight Muriatic in a spray bottle spray it let it chew, wait spray some more keep it wet, then rinse off the scale.

 

[A**holes Garage]

For removing mill scale on smaller pieces, I have a Homer bucket half full of muriatic acid. I also have a small plastic strainer filter basket for smaller pieces, with home made handle.