first time painting - should I grind off the thin surface rust or just apply rust converter?

[wwwfarmer]

Hello everyone!
This is my first time spray painting steel. My plan is to use wipe the implement with a thinner, spray rust converter, use a two component primer followed by two component enamel paint. I've been told I don't need to remove the surface rust because it is so thin. What are you thoughts?


If grinded, I am not sure how much of the surface detail is going to show through the paint.. What tool (angle grinder, orbital sander...), what wheel type(flappy, wire, nylon..) and what grit size is best used to remove thin surface rust that will leave appropriate finish for the paint? I feel like angle grinder is going to make an uneven surface. I don't currently have an orbital sander at home, so I cannot test it. Do you think orbital sander is the more appropriate tool?

 

[Olsen]

I like Ospho for this.

 

[Scar0B2150]

I'd use a wire wheel/ wire cup brush. Wipe clean, prime, and paint.

 

[workinonit]

Cup brush definately. That sounds like overkill for a farm implement but a good plan. What is the implement? Looks like some very nice fab work you did. Those are excel;lent welds. Pics of what you built would be nice.

 

[fried1765]

I like Ospho for this.

DITTO !!!
OSPHO first, then paint and primer.
No need to sand anything there.
OSPHO will adhere to that very light surface rust even better than absolutely clean steel.

 

[Tinhack]

I agree with the phosphoric acid treatment but you need to make sure it is completely dry before priming. It will have a chalky look when dry. If you are painting with a compressor/gun, also make sure your spray air is dry during priming. Use a filter/drier before the hose and blow-out the hose before using it. Drain the filter/drier after each use.

This is cheap insurance when you think about the cost of good paint and all your hard work. Ditto on the excellent welding job. Can't wait to see the finished product.

 

[oosik]

I don't have any implement or tool. So.......scrub it down good with fine grit sandpaper or steel wool - prime - paint.

 

[fried1765]

I don't have any implement or tool. So.......scrub it down good with fine grit sandpaper or steel wool - prime - paint.

NOPE !
OSPHO first!
As described above, allow OSPHO to dry thoroughly, to chalky look.
Then a very light hand sanding+prime+paint.

 

[CoyPatton]

DITTO !!!
OSPHO first, then paint and primer.
No need to sand anything there.
OSPHO will adhere to that very light surface rust even better than absolutely clean steel.

I would recommend the wire cup brush. Your goal not being to remove all of surface rust, but to knock anything loose off. Without this step, it has been my experience that the loose stuff breaks off regardless, but usually after you have treated it, primed it, and painted it. It leaves a bare rust spot that is deal-able but more involved than a quick wire brush treatment prior to cleaning prep work.

 

[fried1765]

I would recommend the wire cup brush. Your goal not being to remove all of surface rust, but to knock anything loose off. Without this step, it has been my experience that the loose stuff breaks off regardless, but usually after you have treated it, primed it, and painted it. It leaves a bare rust spot that is deal-able but more involved than a quick wire brush treatment prior to cleaning prep work.

The OP's pictures do not appear to show any "loose" rust.

 

[Sberry]

None of that crap, scuff or sand the loose off, scuff again with maroon Scotchbrite, blow off and paint.

 

[TractorGuy]

Even with phosphoric acid (Ospho) you should hit it with a wire brush to get the loose stuff off.

I don't usually bother with primer after the acid dries.

 

[fried1765]

None of that crap, scuff or sand the loose off, scuff again with maroon Scotchbrite, blow off and paint.

OSPHO is amazingly effective at creating a bite surface for the primer/paint.
You should try it some time!

 

[Sberry]

It probably is good. I just dont use it, dont use any prep except mechanical.

 

[ArlyA]

After wire wheel or whatever mechanical cleaning, I like to clean the dust off with air hose. If that's not availbe I use paint thinner/acetone mix. Use rubber gloves with that stuff, it cuts everything..

 

[Egon]

It probably is good. I just dont use it, dont use any prep except mechanical.

Then you are leaving rust behind on the metal that will just keep on rusting.

 

[Sberry]

I wonder how it is all my stuff isnt rusting thru? What makes it rust?

 

[Sberry]

A lot of industrial primer is rated for tightly adhered rust.

 

[Deere Dude]

Ospho is good stuff. Beware though; make sure you have old clothes on. Ospho is like water and it is easy you splash it on good clothes and in a few months you will start seeing white sploches all over them.

 

[wwwfarmer]

Thanks for all the good and helpful replies. I didn't mention in my queston (I didn't know it matters at the time) that half of the implement is hardox steel that comes with a primer already on it with only small scratches.. Some not so small areas of S355 steel are also rust free. The pipe was the only problematic part. Phosphoric acid based rust converters are therefore out of the question for half of the machine. I went with this product instead: Rust Converter


This document contains the ingredients: https://www.weicon.de/media/pdf/2a/30/c5/MSDS_111550_EN_EN_.pdf


Never used it before and have no idea how it well it works.