converting rust to inert blob

I've got some rust on top of my steel water tank. As I understand it, I can buy some mystery spray that converts the rust to an inert primer that I can then overcoat with some kind of finish coat (paint? epoxy?). Can I just grab a spray can of the magic goop at Home Depot, or is there some other product that is mo better?

Greetings,
Mr. sbg. I did a bit of research on this a number of years back so things may have changed...

There were/are basically three different systems. From memory.... Rust removers (like Naval Jelly), rust neutralizers (can't remember brand names) and rust converters (like Contra Rust, Neutra Rust).

Not hard to research but there is also the POR 15 option which is a coating and actually relies on a layer of rust to promote bonding.

Supposed "rust" paints like Tremclad, I wouldn't bother with.

I've used Rustoleum Rust Restorer in a brush on form in the past on cars with good results.
Next time I'll look for a spray.

Might want to look into ospho, I've used it in the past on old trucks.

Ospho

The Por 15 is a very good product. Follow the directions. It lasts!

Ospho does exactly as asked.

I've used it on the boat and it works as advertised.

I tried the Rustoleum rust converter spray can, and it did not work for me.
Blobs of rust? scrape them off first.
First thing is scrape off any flaking loose rust. You can use a sharp metal scraper, chisel, etc..
Then I would scrub the top with a SS scrunge and dish soap and water.
Rinse and dry it off, then overcoat with something.

My wife buys these SS scrunge pads at dollar store, and they actually cut the crud very well including light rust.

I have rust appearing at the stanchion bases on our railings, both at the bottom where it leaves rust streaks, and around the top where the rail fits in. (boat lived its first 21 years in salt water) I have tried FSR with bronze wool and a toothbrush with a some success, but it's labor intensive. I have also used ZEP Beststuff, but it's a lot of work as well.

Greetings,
Mr. P. For stainless steel I've found this is by far the best and easiest:
Spotless Stainless Home
but I think Mr. sbg is after something different.

I have chased rust for years and used osphos and it does what it says it does which is chemically change rust but it only works where it touches, you still have sand / or brush it off and reprime and paint. I would now vote for POR-15. Excellent stuff and as mentioned above it covers the rust. Use as directed two coat minimum. The areas that I have done are still rust free. Sand slightly after the second coat and paint with whatever you are using as top-coat.

RT Firefly said:

Greetings,
Mr. P. For stainless steel I've found this is by far the best and easiest:
Spotless Stainless Home
but I think Mr. sbg is after something different.

Click to expand...

Now that appeals to my lazy side! I will definitely try it.

Another vote for por15, it actually works well.

RT Firefly said:

Greetings,
Mr. P. For stainless steel I've found this is by far the best and easiest:
Spotless Stainless Home
but I think Mr. sbg is after something different.

Click to expand...

I looked into this, it is 17% citric acid.
Have you used with "Spotless Stainless"?

"Rust converters" are a legitimate treatment - within their legitimate scope of use. The industrial products I have experience with pretty much perform as advertised. The basic chemistry uses tannic or phosphoric acid to react with the iron oxide (rust) to produce stable ferric tannate or ferric phosphate (respectively) as the reaction product. These are pretty much stable and are suitable for coating.

I only suggest its use where conventional abrasive blast or mechanical cleaning cannot be practically employed due to site conditions and/or cost.

The trick is, the acid solution must come in contact with the rust. The products I'm familiar with also contain an organic solvent to promote the penetration of the solution. In practice, this means mechanically removing as much rust as possible prior to application. It accomplishes nothing to treat the outer layer of flaking rust. This also means that oil, grease, paint, etc. must be removed prior to application.

An ideal application scenario is where the rust on the surface, with no or little flaking. It's not going to help a lot with cancerous and deeply pitting rust. There's a NAVSEA (Naval Sea Systems Command) study out there from 15-20 years ago that compares half a dozen or so of these products in maritime lab simulations, almost all of which are still on the market. Conclusion - some are better than others, depending on acid strength and the effectiveness of the organic solvent.

This was discussed within the past year or so in a TF Maintenance thread, but durned if I can find it. I want to say that FF posted a "home brew" of liquid dish detergent (organic solvent) and muriatic acid that does the job.

Greetings,
Mr. 717. Yes, Spotless Stainless IS citric acid and it is the best, bar none, remover of rust on stainless I've ever tried BUT, OP is looking for a different product. Spotless Stainless would NOT be suitable for his purposes.

Muriatic acid would remove rust quickly, of course it is dangerously strong.

Much safer to use white vinegar. Best if the surface is completely covered in a layer of vinegar and will take a few days. Alternative is molasses, surprisingly works well for rust.

A tank top would need a dam on the edges to hold the rust removers. All the rust could be gotten rid of in a few days of scrubbing and waiting and scrubbing and waiting. May not be practical to do for this tank top. I have removed plenty of rust by submerging items in vinegar.

I cleaned some very rusty cylinder heads in vinegar. Let it work for a few days, then spray with power washer, dig at rust with screwdrivers, soak and repeat. It dissolved out packed in rust from all the water chambers, and hurt no cast iron metal.