How to paint steel-framed windows showing signs of rust?

Question

Hi, I've got 4 large (~4.5m x 2.5m) steel framed windows at my house that are starting to show signs of rust on their exterior side, mainly on the horizontals. It's looking like a somehwat dauntingly large job, so I'd like to do it as quickly and efficiently as possible. I've got a few queries that I'm hoping the community / experts can assist with:

* To half my work, I think I'll just do the exteriors of the windows, and leave the interiors for now. I'll be trying to match the new paint to the old, which I believe is Colourbond Monument, but is it likely to look bad with the likely mismatch? I'm hoping not given the glass interface inbetween.
* Do I need to sand and prime with this level of rust, or could I just paint with something like this, which claims to not require a primer on lightly rusted steel: https://www.bunnings.com.au/white-knight-rust-guard-4l-black-flat-epoxy-enamel-paint_p1568447 
* If sanding & priming is required, can I just do that on the rust affected areas, and just do the final paint layer on areas that don't look rust affected, as well as usuing a rust coverter for any hard to reach places?
* If everything needs to be sanded back, I'd think a detail sander such as this would be the way to go? Or will that be a risk of sanding the metal back too far and/or damaging the glass from the vibration?https://www.bunnings.com.au/ryobi-180w-multipad-sander-rms180-s_p6210548 
* I am hoping to not mask around every pane of glass, and just painting the frames carefully with a brush rather than spray paint, with the sealant providing a bit of a buffer between the metal and glass. Am I dreaming?
* Shoud I alternatively be looking at removing the sealant (is this generally just silicon?) and glass panes, and how easy is that to do? I'm a bit scared of this option for risk of damaging the glass, but it would make painting the interiors at the same time as the exteriors a lot easier and more easily allow for spray painting.

Some photos of the windows as below - the last is an example of the interior, to show that it isn't rust affected. Thanks in advance for any assistance!

chiraag · Answer

Thanks for the advice Eric, much appreciated. Will definitely be doing the job in sections on days off over a number of weeks I think.

Was hoping for some confirmation that my shortcuts would be OK, but your advice has confirmed that I should just take my time and do the job properly!

EricL · Answer

Hello @chiraag

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your steel framed windows.

Just a friendly reminder that working with glass is dangerous an accidental hit with a tool or when excessive force is used could make the glass shatter and cause injury. Please remember to wear personal protection such as appropriate clothing, gloves and goggles when working around glass.

* It will be noticeable that the front of the frame has been freshly painted. Getting an exact colour match will be difficult. I recommend doing a light revamp of the interior frame and sanding it down as well so that you can cover it with a fresh coat of paint. With both sections painted it will look uniformly fresh and new.
* I understand your desire to make the revamping process as quick as possible. But with the current rust level on your frames, I suggest sanding everything down in order to have a uniform painting surface. Extra sanding of course will be needed on those sections with heavy rust.
* As mentioned in question number two, it would be best to sand everything down. In regards to the heavily rusted areas, it's best to treat it with rust converter.
* It is difficult to tell how badly the vibration will travel through the steel frame and then to the glass. If you can borrow a friends or neighbours tool you could test it and see. Otherwise, I suggest manually sanding the frame for safety.
* I recommend masking the seals and glass in order to get a clean uniform finish with no overpainting. 
* Your window currently has a custom fit rubber gromet sealer. it is installed with a special tool that locks it in place. Using a silicone sealer might be possible, but if you are not familiar with glazing installation practices, it would be best to leave this to a professional.

Your project may seem daunting but is actually achievable. I propose doing the repainting in sections rather than doing it all on one go. By taking your time, you'll be able to concentrate and remove all the rusted sections properly. The job will be accomplished in a manner that is not rushed and you won't miss small sections that could cause all that hard work to rust again.

Here is a handy step-by-step guide: How To Paint Metal

If you need further assistance, please let us know.

Eric