Painting over rust on heating pipes

Question

I live in an older apartment building (circa 1968-69). I just stripped layers of old paint and putty off of the heating pipes in my bathroom. I'd like to repaint them with silicone-based acrylic paint, which I read is very moisture-resistant. However, there are some spots that look a little rusty (not rusted through - these are thick iron pipes.) Is it a good idea to put the acrylic paint directly on the rust, or does it need to be treated first? I don't think that Rustoleum is used on heating pipes, unless I'm wrong about that.

Thanks in advance for any advice!

Answer 1

I find rust converter products do not work at all for me; however my stuff lives outdoors and is subject to moisture. I've had "rust converted" areas utterly destroy a top tier LPU paint job, by re-rusting at the "converted" areas - and yes, I wire-wheeled before application.

NASA knows a great deal about corrosion (Who picked this site on Cape Canaveral? Kruschkev?) and has a whole division that does nothing but figure that stuff out. They had a liberal-arts major reorganize their website, so the good stuff is now hidden and/or entirely taken down, but their view was that best results are had by sandblast, a close runner-up being needle scaling or grinding to SSPC-PC10 near white metal, and then a quality primer and paint. They recommend a 2-part mil-spec chromate primer (green stuff seen on airplanes) but I find Rustoleum 7769 Rusty Metal Primer works astonishingly well for a product that is safe to sell to consumers.

They feel a distant second-best is aggressive power wire-wheel treatment. In my experience, that, plus Rustoleum 7769, holds very well if you can keep it extremely dry before application, and do a thorough solvent wipedown. You would need to check Rustoleum 7769's label to see if it can work on things that get as hot as those pipes. It works fine on things I paint black and put in direct sunlight, so they are getting up to 190 degrees F / 90C or so.

Give the 7769 a few days to cure, and it should accept an alkyd primer like KILZ Original or emulsion/latex primers like KILZ anything else. Anything they sell for architectural paint will be emulsion/latex, which performs poorly as a paint, but it is popular for non-performance reasons like reducing regional smog (VOCs), minimizing "stinky" time, and using less scary chemicals.

Answer 2

I have used rust conversion products such with good results.

Used the Rust Reformer product on a metal staircase and painted with an oil based paint. No rust has become evident after 6 years.

I have used the rust reformer products on an automotive project and got the same results. The product converts rust to an inert substance that can be painted. I think You can use the same process on your heating pipes.