Technical BLACK Rust How to remove?

Doing some body rust repair and found black rust in between two close panels. I am having a bear picnic of a time trying to remove it. Its dark brown nearly black. After sanding shining a flash light on it and its nearly as smooth and shiny as the clean metal around it.

36 grit cubitron resin disc on angle grinder barely even touches it! 24 grit on a belt 40 grit flap disc on angle grinder both hardly do a thing.

Naval jelly and rust remover gels and even muriatic acid dont seem to really even disturb it.

It acts like mill scale where its almost too hard and just gets polished like the grit cannot dig and just skates across it. Its really absurd. Its sheet metal and not too pitted so I dont want to go crazy heavy on the pressure with it and blow holes everywhere.

Would appreciate some help here before I bust out the small blaster and shoot grit everywhere.

 

How about a picture of the area you are trying to get to? Its hard to make a suggestion without seeing how much room you have to work with.

 

Are you sure it's not asphaltum sound deadener?
A warning about Muriatic acid, it can chrolonate the steel making it prone to rust.

 

I got all the room in the world. What are you suggesting?

 

Nope its not this. I would have noticed it build up and the many abrasives I have used and the poking about. I thought at first it might be very hard seam sealer or something but 36 grit on a angle grinder would eat it up.

 

Sandblast

 

I use a cut off wheel to remove that black rust, just running lightly over it, seems the quickest to me. WEAR A MASK, that’s the stuff jewellers rouge is made of, also cut into stones and called black Alaska diamond, proper name is hematite

 

Did you mean "closed" rather than "close" panels? I got the impression you didn't have much room to work.

Have you tried one of those "mini" hand held sandblasters? Leaves a lot of particles to vacuum/blow out when done, but the one I have did a nice job on some had to get to rust. Pattern is small enough not to heat the sheetmetal and cleaned it really well. I used the black coal slag I took out of my regular cabinet sand blaster.

 

A 60 grit flap disc on your angle grinder will knock it off but in most cases the underlying metal will be severely pitted. Sandblasting will dig out the pits better and be easier to get in close quarters but the results will vary depending how severe it is.

 

Sandblast or use molasses. The latter will take a week or two but will chemically remove all the rust.

 

Thanks for the added info. I had considered using a cutoff wheel as well. Great minds and all.

 

I should have been more clear. The panels were close off before I cut away at one to repair the rust and found black rust on the other panel. I should have just started with my mini blaster but I hate using it as its so messy and lying in the sun covered up is no fun either!