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

[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.