Rust coming back

[weswebb]

I have an outdoor metal spiral staircase that leads to a roof deck. Had the entire staircase and railings professionally painted one year ago because of areas of rust. Supposedly rusty areas were prepped, primed with bare metal primer and painted. Rust is starting to come through the small platform at the top of the staircase that connects with the concrete deck. See pic. Note surface is not flat but has small "bumps". There was 2 year guarantee so painter says he will fix this area. I suspect he will just paint over it.
QUESTION: is there any type of coating I can apply over the paint to protect this area? I was even thinking of Flex Seal but the last thing i want is to water to get under any coating. This area has only modest foot traffic as deck not used frequently. Southern California does not usually have much rain but last winter there was plenty.....and the area is foggy in the morning. It would be hard to cover this area with plastic as it is very windy and water might get under it making it worse.
Any ideas appreciated!

 

[Snoonyb]

Diamond plate, because of the texture, will be prone to rust and oxidation and while durable, needs attention.

Given your area, were it I, I would have it wire brushed and primed with a rust inhibiting primer and not top coated until next spring, when its warmer.

On metal decks, in the LA basin, I used LIFE PAINTS #39 primer.