How do I prep a metal security door for paint?

Hi Jon, perhaps this post will help you, as it outlines the basic steps. https://homeguides.sfgate.com/restore-rusted-metal-door-46121.html

Make sure it's clean and free of grease and dirt. You can buy paint that will cover the rust so that shouldn't be a problem. Look for a primer that is made for rusty metal.

We have metal security doors also. Last year we sanded ours, pressure washed it and let it dry overnight, then applied some Rustoleum in a spray can. Found the hard way that using a roller or brush tended to plug up the holes on the door. Anyway that stopped the rust problem and the doors look like new. You can find lots of Rustoleum products at very good prices that are shipped to your door at Amazon.com

Sand off the rust and any gloss. You need to use DTM, direct to metal, paint. Sherman Williams and Behr have it.

Hi Jon,

I'm Linda. As Adrienna wrote, first clean it well. Next you'll want to sand all of the places that have rust. Make them as smooth as possible. Then clean those areas and wipe the entire door down again. Get some Rustoleum primer for your door. If you have a place to use the spray outside, that is the best to use. If not, use the painted on kind. I'd use a foam brush to eliminate brush marks. Let the door dry and cure according to the paint can directions. Once that's done, you can paint it any color you want, again using Rustoleum or even latex outdoor paint. I hope this helps you. Wishing you success!

Thank you all for your recommendations. I will let you know how it goes.

Do you mean the wrought iron grated kind?Use a stiff wire brush to get to all loose rust from the crevices between grating and around frame then use some vinegar and Dawn dish soap for all dirt and grime with the stiff wire brush,then rinse well,let dry really well then you'll need to spray paint it,can't brush or use roller. If you take it off might be easier you can do one side then the other. Also when you rehang spray hinges,lock & door handle mechanisms with WD-40 Dry Lube(so dust and dirt won't stick in/on them). I just did one of mine and had some trouble getting dust,debris,rust out of frame on bottom of door where grating connects,if you have power washer this area would be easier if not you'll need really strong nozzle on hose. You can just tape baggie over door handle, dead bolt area or remove it for painting. I was dreading doing it but it was much easier than I thought,and looks so much better really perked up whole entrance. I used lighter colored paint so it wasn't so dark/dreary when done(it was black).