sand rust before repainting ironwork?

[JayBearII]

In a bygone era, I used to live on Beacon Hill in Boston, famous for its decorative ironwork on houses. There, I learned that one needed to sand off the rust before priming and repainting. But that was then and this is now. The guy who hopes to repaint the ironwork on the windows and doors of my condo is telling me that one can spray some kind of primer on the ironwork and then repaint, no tedious sanding required. I am dubious, but of course that route would be a lot less effortful for him and less expensive for me, so would you experts out there please advise? (As to how much rust we are talking about, the rust is not extensive, but it is noticeable upon inspection if your eyesight is good.)

[diandbeau]

Rust is rust.  Needs to get gone.  Sorry, but covering it up sounds like a bad idea.

[bdmowers]

I painted in the US for many years.......yup, rust will out. It is a chemical reaction happening, not a "discoloration". It will work thru anything you put on it. Gotta get rid of it, sorry, I know what a pain it is. But do it once, prime and paint it, two coats, and you`ll be done with it. You can sand all the rust off (yeah, right!) then paint and you may not see the rust for a year but .......rust is oxidation and the tiniest amount of it will burn through the paint then you`ll have to do it all over again. Do it right with a metal primer even if you have to go to Guad for it.

Another bit of caution. Most painters here consider primer to be flat white paint. Real primers are something else entirely.  Primers are special substances with particular elements included to neutralize bacteria, cover discoloration, react with ("hold onto") the surface underneath and to the top coat, etc. You will need a metal primer which is different from wood primers and much stronger. In the US, there were combination metal primers/paints that worked well enough (Rustoleum, etc.) . I don`t know of a real primer here lakeside but perhaps others do and can recommend one.

[jrm30655]

We used to use some stuff called "Naval Jelly" or maybe "Navel Jelly"   I have no idea if you can even get it anymore because it was nasty stuff.

We'd use it on bare metal by wiping it on, washing it off, drying it and painting with Rustoleum.

We'd leave tools out on a construction site and in 3 days in the south, they are rusted.  That stuff was fantastic to clean them up.

If it were just light rust, I might be tempted to try CLR (Superlake)  That stuff seems to work on almost everything

[Ezzie]

Yes, you need to sand and prime the metal before repainting it or it won't last very long.  One of the best "off-the-shelf" spray can primers is available here at Home Depot and is a Rustoleum product called "Self Etching Primer" in light grey.  Works very well.  For larger jobs, treat bare metal with a diluted solution of phosphoric acid before applying a good metal primer is also a very effective way to prepare a metal surface before applying top coats.

[windstar]

We used a spray called Rust Stop ??  on our badly rusted boat lift in Florida.  That was in salt water & so badly rusted it was coming off in sheets.  This stuff caused a chemical reaction that hardened the loose rust & bonded it to the metal that was still there.  This made it look nice for the condo ###.  Lasted about 4 years & may still but we have not been there.  So yes it works well.  Then was only available in black.   On the other hand I would rather have nice window frames done properly with sanding & primer.

[lcscats]

Chemical changes rust into something else than you paint is the theory. 

[mudgirl]

In Mexico I have known the iron workers to use either grey metal primer or orange, which they call "minio". They will most often use the grey, because it is cheaper. However, the grey only works long term on galvanized or aluminum, for iron you want the "minio"- insist on it. Buy the primer yourself and do not let your iron worker add more than 10% thinner to it. My welder in Bucerias does beautiful, artistic work, but he SUCKS at the painting- everything he has done for me has had to be repainted within a year (remember, it is much more humid here on the coast). One time I asked him to leave me a little of the minio so I could touch something up- when I went to use it, I found that it was so thinned out that it was like thinner with some orange paint in it, rather than paint with a bit of thinner!

[bdmowers]

11 hours ago, mudgirl said:

In Mexico I have known the iron workers to use either grey metal primer or orange, which they call "minio". They will most often use the grey, because it is cheaper. However, the grey only works long term on galvanized or aluminum, for iron you want the "minio"- insist on it. Buy the primer yourself and do not let your iron worker add more than 10% thinner to it. My welder in Bucerias does beautiful, artistic work, but he SUCKS at the painting- everything he has done for me has had to be repainted within a year (remember, it is much more humid here on the coast). One time I asked him to leave me a little of the minio so I could touch something up- when I went to use it, I found that it was so thinned out that it was like thinner with some orange paint in it, rather than paint with a bit of thinner!

Where can one get "minio"?

[mudgirl]

You can buy "minio" at at Prisa, Comex, any paint store should have it. Most welders like to spray rather than use a brush. Spraying does give a more even coat, gets in the fiddly little corners easier, and is, of course, faster.  Problem is that they have to thin it out so much to get it to flow easily through the spray nozzle- so if they are going to spray, ask that they thin as little as possible, and do at least 2 primer coats. Suerte.

[bdmowers]

Thanks, mudgirl, great advice.